EUFRAT User Meeting

“Progress of Nuclear Data Measurements using JRC's unique facilities”

JRC-Geel, Belgium

4-7 December 2017

Public 2017

MONNET

GELINA

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Title EUFRAT User Meeting “Progress of Nuclear Data Measurements using JRC's unique facilities” Abstract The EUFRAT user meeting will give an overview of the recent achievement using JRC's unique nuclear data facilities

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I EUROPEAN COMMISSION DIRECTORATE-GENERAL JOINT RESEARCH CENTRE Directorate G – Nuclear Safety & Security G.2 - Standards for Nuclear Safety, Security and Safeguards

Agenda EUFRAT user meeting 4-7 December 2017, JRC-Geel, Belgium

Monday, 4 December 2017

10:00-12:00 Arrival and Registration 12:00 Lunch

13:00 Opening session

13:00-13:15 F.-J. Hambsch, W. Mondelaers: Welcome

13:15 Session I (Chair: F.-J. Hambsch)

13:15-13:45 M. Hult: "The Radionuclide Metrology Laboratories of JRC-Geel"

13:45-14:30 A. Ianni: "Importance of underground labs for science and technology"

14:30-15:00 V. Tretyak: "Search for rare decays in nuclear physics"

15:00-15:30 B. Lehnert: "The Importance of Rare Nuclear Decays"

15:30-16:00 Coffee Break 16:00 Session II (Chair: S. Pomme) 16:00-16:30 A. Kirsch: "Developments and future plans for large scale double beta decay experiments"

16:30-17:00 W. Schroeyers: "Towards a sustainable society by adequate measures to reduce impact of NORM"

17:00-17:30 T. Croymans: "Towards a sustainable and safe construction industry: a radiological assessment on the reuse of by-products in construction materials"

17:30-18:00 A. Fenyvesi: "Counting of activation detectors at ultra-low level background facilities: Measurement of fluxes of charged particles escaping fusion plasmas at KSTAR"

18:00 Closure, day 1

18:30 Workshop Reception

21:00 End

II EUROPEAN COMMISSION DIRECTORATE-GENERAL JOINT RESEARCH CENTRE Directorate G – Nuclear Safety & Security G.2 - Standards for Nuclear Safety, Security and Safeguards

Agenda EUFRAT user meeting 4-7 December 2017, JRC-Geel, Belgium

Tuesday, 5 December 2017

8:45 Session III (Chair: M. Hult)

8:45-9:15 M. Charette: "Radium Isotopes as Tracers of Hydrothermal Activity in the Deep Ocean"

9:15-9:45 S. Vanderheyden: "Adsorption of caesium on different types of activated carbon"

9:45-10:15 N. Horemans: "Uptake of radionuclides in plants: a case study on rice (Oryza sativa) exposed to radiocaesium" 10:15-10:45 Coffee Break 10:45 Session IV (Chair: S. Kopecky) 10:45-11:30 A. Junghans: "Nuclear Data for applications"

11:30-12:00 M. Kerveno: "Neutron inelastic scattering studies with GRAPhEME at GELINA" 12:00-12:15 L. Salamon: "Time-of-flight measurements on natural Ag and MINERVE Ag samples at GELINA facility" 12:30 Lunch 13:30 Session IV (Chair: P. Schillebeeckx) 13:30-14:00 P. Leconte: "Integral Experiments in the GELINA Target Hall on 238U"

14:00-14:30 G. Tagliente: "Accurate measurement of the 92Zr and 89Y neutron capture and transmission cross section" 14:30-15:00 A. Olacel: "Neutron inelastic scattering measurements performed at the GELINA neutron source" 15:00-15:30 E. Party: "Neutron inelastic scattering studies on 232Th : from measurements at GELINA to reactor applications" 15:30-16:00 Coffee Break 16:00 Session VI (Chair: J. Heyse) 16:00-16:30 L. Leal: "Nuclear Data for Criticality Safety Applications at IRSN" 16:30-17:00 M. Pillon: "Integral Benchmark Experiments on a Large Copper Block using GELINA" 17:00-17:30 E. Berthoumieux: "Segmented mesh Micromegas and its associated electronics: development for a neutron beam profiler"

17:30-18:00 A. Krasa: "Characterisation of Bi-samples by Neutron Resonance Capture Analysis"

18:00-18:30 S. Fiore: "Epithermal/fast Neutron beam monitoring at GELINA time-of-flight facilty using Uranium-coated single crystal diamond detector"

18:30 Closure, day 2 18:45 Dinner 21:00 End III EUROPEAN COMMISSION DIRECTORATE-GENERAL JOINT RESEARCH CENTRE Directorate G – Nuclear Safety & Security G.2 - Standards for Nuclear Safety, Security and Safeguards

Agenda EUFRAT user meeting 4-7 December 2017, JRC-Geel, Belgium

Wednesday, 6 December 2017

09:00 Session VII (Chair: S. Oberstedt) 9:00-9:45 O. Serot: "Investigation of Nuclear Fission thanks to EC-JRC Geel facilities" 9:45-10:15 S. Pomp: "Experiments on ννν(A)"

10:15-10:45 K. Jansson: "Developing the VERDI spectrometer and the 2E-2v method for measurements of correlated fission properties"

10:45-11:15 Coffee Break 11:15 Session VIII (Chair: A. Göök) 11:15-11:45 A. Oberstedt: "ELI-NP and EUFRAT - status of a collaboration"

11:45-12:15 F.-J. Hambsch: "Absolute and relative neutron-induced fission cross section measurements of 235U, 238U, 237Np and 242Pu at NPL and JRC-Geel"

12:15-12:45 M. Angelone: "High-resolution measurements of the 12C cross sections for the (n,pn), (n,dn) exited states"

12:45 Lunch 13:45 Session IX (Chair:C. Paradela) 13:45-14:15 C. Weiss: "Diamond detector measurements at VdG/MONNET and GELINA"

14:15-14:45 P. Schillebeeckx: "Assessment of the EJ-200 plastic scintillator as an active background shield for neutron detection systems"

14:45-15:30 K Eberhard: "Fabrication of thin actinide layers for applications in nuclear chemistry and -physics"

15:30-16:00 Coffee Break 16:00 Session X (Chair: G. Sibbens) 16:00-16:30 B. Laurent: "47 mg of 239Pu in a fission chamber for prompt fission neutron spectra measurements"

16:30-17:00 B. Jurado: "Investigation of the surrogate-reaction method via inelastic-scattering reactions on 240Pu"

17:00-17:30 F. Mingrone: "Nuclear Data at n_TOF"

17:30-18:00 J. Wagemans: "Fast neutron detector development for measurements at the VENUS-F reactor"

18:00-18:30 I. Meleshenkovskii: "Measurements on U and Pu standards with medium resolution gamma-ray spectrometers"

18:30 Closure, day 3 19:00 Conference Dinner (Flore) 22:00 End IV EUROPEAN COMMISSION DIRECTORATE-GENERAL JOINT RESEARCH CENTRE Directorate G – Nuclear Safety & Security G.2 - Standards for Nuclear Safety, Security and Safeguards

Agenda EUFRAT user meeting 4-7 December 2017, JRC-Geel, Belgium

Thursday, 7 December 2017

09:00 Session XI (Chair: M. Betti) 9:00-9:30 R. Jacqmin: "Importance of EUFRAT for the nuclear data community" 9:30-10:00 R. Capote: "Importance of EUFRAT in the wider community"

10:00-10:30 P. De Felice: "Importance of EUFRAT for the radionuclide community"

10:30-11:00 Coffee Break

11:00 Session XII (Chair: F.-J. Hambsch) 11:00 -11:30 A. Plompen: "Importance of European Projects (CHANDA, ERINDA, EUFRAT,...) for the Joint Evaluated Fusin and Fission (JEFF) file” 11:30-12:00 A. Bucalossi: "Open access from the point of view of the JRC"

12:00-12:30 W. Mondelaers: "Launch of the new EUFRAT scheme"

12:30 Lunch

14:00 End

1

The Radionuclide Metrology Laboratories of JRC-Geel

Mikael Hult*

European Commission, Joint Research Centre, Directorate for Nuclear Safety and Security, Unit G2. Retieseweg 111, 2440 Geel, Belgium.

1 Historical overview of the JRC's ratios). The RN-staff was also involved in evaluation of RadioNuclide Metrology Laboratory decay data and the works of e.g. Bambynek et al. on X- ray fluorescence yields and electron capture probabilities The JRC's RadioNuclide Metroloy Laboratory (RN-Lab) etc. [4, 5] have been highly cited. Much of the decay was formed as a consequence of the EURATOM Treaty data measured at JRC-Geel is still taken into account [1]. Article 8 states that "The Commission shall establish with high weights when new evaluations of decay data a Joint Nuclear Research Centre" and continues "It (the are performed. A nice example of this is the excellent JNRC) shall also ensure that a uniform nuclear work of Vaninbroukx et al. in 1981, which even today terminology and a standard system of measurements are stands out shown by Fenwick et al. (2016) [6]. Together nd established. It shall set up a central bureau for nuclear with the 2 JRC-measurements in 2011 they agree very measurements (CBNM)". In 1993, CBNM changed its well with the evaluated data (red line in Fig. 1). In this name to IRMM (Institute for Reference Materials and context it is important to point out that a great number of Measurements) and in 2016 it became JRC-Geel. decay data have insufficient accuracy for adequate use today. Many old measurements were performed with the In 1959, the first staff of CBNM working in the RN-Lab main objective to understand nuclear structure and not to had their offices at the neighbouring institute, SCK•CEN provide metrologically perfect decay data. Today, new (The Belgian Nuclear Research Centre). In 1960 The improved instruments and advanced computer RN-Lab started installing equipment in the newly simulations have enabled us to take leaps forward in constructed "Main Building (010)" at CBNM. The early producing better decay data. work focussed on building a capacity for primary standardisation of radioactivity, i.e. to measure activity using methods and instruments that do not require the 465 Half-life of 109Cd use of sources for efficiency calibration. Dedicated 464 instruments were developed for e.g. defined solid angle X-ray and alpha counting [2], 4πβ-γ-coincidence 463 counting and source preparation. Other important 462 developments included the realisation of a CsI sandwich 461 detector which has close to 100% efficiency for certain DDEP (± 1 σ) radionuclides and therefore gives results that have a high 460 weight when key comparison reference values are 459 calculated at BIPM. Furthermore, early work on what eventually became the CIEMAT-NIST technique for 458 CBNM Chalk RiverChalk NPL NIST PTB CEA IRMM Liquid Scintillation Counting was performed by Bert 457 Coursey from NIST (formerly NBS) [3] during his sabbatical stay at CBNM.

These (and many more, as this is not a complete account for the work) instruments and techniques were Fig. 1. Published data, with combined standard uncertainties, on the half-life of 109Cd and the evaluated value (purple line). eventually used for realising the unit Bq in close Older measurements (starting in the 1940s) have been excluded collaboration with world-wide National Metrological following the recent evaluation of Bé [7]. Institutes (NMIs) and for producing highly accurate decay data (half-lives, emission probabilities, branching

* Mikael Hult: e-mail address: [email protected] 2

The Chernobyl accident in 1986 triggered the RN-Lab to Japan on September 30, 1999 was an important start a low-level group with activities involving demarcation line as it showed that the underground measurement of environmental radioactivity and low- measurements in HADES had left the exploratory phase levels of radioactivity. In 1992 Rainer Wordel and and could provide data important for supporting policy Daniel Mouchel started a collaboration with SCK•CEN makers. Following the accident, the EC President Prodi by installing a HPGe-detector in the 225 m deep offered help to Japan and help was also requested to underground laboratory HADES. SCK•CEN built the measure low-levels of neutron activation induced in laboratory to study possibilities for the final repository of samples collected in the homes of people living near to Belgian nuclear waste. It turned out that it was the JCO site. This information was important in order to excellently suited for ultra low-level gamma-ray establish what the consequences of the accident were. spectrometry as the flux of cosmic ray induced muons is Since then, numerous projects have been carried out in about a factor of 5000 lower compared to above ground. HADES providing support in many different fields However, taking a Ge-detector from above ground and ranging from solving the Hiroshima enigma [8, 9] and placing it in HADES was not optimal, as minute characterising reference materials to radioecology and amounts of radioactivity in the detector affected the oceanography. Figure 2 exemplifies this as it shows the background. Therefore, early work focussed on finding RN-Lab competences of performing reference radiopure materials (materials with very low levels of measurements and producing reference materials is natural radioactivity) that could be used for detectors and essential in basically all fields where radioactivity shields to be placed in HADES. measurements are performed. And, since radioactivity is everywhere, it follows that the unique installations in the Eventually, the JRC mission moved towards a customer RN-Lab contributes to the foundation of generating a driven scientific and technical support to EU-policies, society based on accurate data that is accepted world- and consequently, so did the work of the RN-Lab. For wide. the HADES-work, the JCO accident in Tokia-mura, .

Fig. 2. The core competence of the RadioNuclide Metrology-Laboratory (mid-circle) supports all aspects of society where radioactivity measurements are needed. 3

In 2003, The RN-Lab started a close collaboration with The EURATOM Treaty includes many aspects that are DG ENER in realising Article 35 of the Euratom Treaty. perhaps more important today compared to when they It states that the Member States (MSs) shall "carry out were formulated. Chapter 3 on Health and Safety continuous monitoring of the level of radioactivity in air, (Articles 30-39) is one such part. The number of water and soil and to ensure compliance with the basic laboratories that monitors radioactivity in the standards" and that the EC (supported by the JRC environment is increasing each year. As an example, the following Article 39) shall have the right to verify this. IAEA network Almera (Analytical Laboratories Whilst DG ENER can visit some 2 to 5 specific Monitoring Environmental Radioactivity) grows with installations per year, the work of the RN-Lab is nicely about 6 laboratories per year and has at the moment 164 complementary as it assesses every MS each 18 months members. Also countries without nuclear facilities (more or less) by organising proficiency tests (PTs) on realise that they need to have competences and facilities specific radionuclides and matrices. The first PT for measuring radioactivity correctly as radioactivity organised by the RN-Lab in 2003 was on 137Cs in air- does not stop at borders. filters. The 137Cs solution was standardised by IRMM and drop deposited on air-filters that were sent to IRMM The medical use of radioactivity is also growing. New by each participating laboratorya. The most recent PT treatments involving different radionuclides require was carried out 2017 and involved 120 laboratories more and precise decay data to be measured and primary measuring 131I, 134Cs, 137Cs (and the primordial 40K) in standards to be produced. A very interesting current maize (a very common feed). They were asked to both topic is the use of theranostics, i.e. radioisotopes of the provide emergency reporting (within 48 hours) as well as same element (e.g. Sc, Cu, As and Tb) that can be used routine reporting (within 1 month). for both diagnostics as well as therapy.

For each PT, a Reference Material is used and it must be An important aspect that is not given as much attention a stable material with well-established reference as it deserves is the realisation of the unit Bq, which is activities for the PT to be able generate results that can done at the BIPM through establishment of key trigger DG ENER to act on the results as well as to comparisons. Like for other units, there is development enable the participants to use the results when seeking in this field and JRC-Geel is much involved in accreditation. The production must follow ISO Guide 34. contributing to it. Recent (highly cited) claims that the As a consequence of this work, a bilberry materials with law of exponential decay may not be valid have been certified activities of 90Sr, 137Cs and 40K that was used in addressed in the most structured study up to date by a PT eventually was accepted as CRM (Certified Pommé et al. [10]. All claims could be refuted and Reference Material) and put in the IRMM catalogue of therefore the present SIR-system (International CRMs in 2015. There are plans, and ongoing work, to Reference System for radioactivity) could be defended. produce more CRM with certified activities of It (the SIR) has recently been expanded to cover also radionuclides as there is a great shortage on this world- short-lived radionuclides (via use of transfer wide. In this context it is worth to point out that the RN- instruments) and pure beta emitters (via use of liquid Lab was accredited by Belac for ISO17025 (under the scintillation techniques). flexible scope) and ISO 17043. As stated in the previous Chapter, JRC-Geel, works in An important aspect of the work of the RN-Lab was the collaboration with the EU and international community possibility to anchor work in the international to improve radioactivity measurements and decay data. community and have a close and open communication In recent years, the open access to RN infrastructure (as with NMIs world-wide. It has mainly been realised stipulated by Euratom Treaty Article 6) has become an through actively working in international organisations important tool in that context. Table 1 lists 22 projects like the ICRM (International Committee for that were accepted by the PAC (Programme Advisory Radionuclide Metrology), the CCRI (Consultative Committees) since the RN-Labs joined the open access Committee for Ionising Radiation) and at Euramet's programme in 2014. Some of these projects are Technical Committee for ionizing radiation (chaired e.g. presented at the conference at JRC Geel, 4-7 December by Dietmar Reher from IRMM). JRC staff has held, and 2017 (these proceeding). The list does neither include is holding, important positions in all these committees the rejected projects nor the projects that were approved and have at several occasions organised conferences and but cancelled. The projects in Table 1 (several of them meetings for these committees and organisations. are still in the starting-up phase) have at the time of writing this resulted in nine articles in international refereed journals and contributed to one Master Thesis, one finalised PhD Thesis and another PhD Thesis in 2 Current situation and open access manuscript.

a There is no standard on the type of air-filter to be used and consequently there is a great variety on the types of air-filter that is used in the EU. 4

Table 1 Overview of open access projects that were approved (and confirmed) for execution in the RN-laboratories. Out of the 22 projects in Table 1, 15 were carried out in EUFRAT Title Institute HADES and 7 in the above ground laboratory. As a number consequence of the open access, it was possible to put Inst. Physics, New method for pulse shape increased efforts in establishing a robust (but still 11-14 discrimination for BEGe Jagiellonian University, flexible) method for quantitative data analysis of detectors Krakow Development of adsorbents for gamma-ray spectra. This work was presented at the most 14-14 remediation of radionuclides in Hasselt Univ. recent ICRM conference [11] and is important as contaminated waste-waters gamma-ray spectrometry is to some extent involved in Measurement strategy for the vast majority of EUFRAT projects in Table 1. 12-14 Geopolymers with NORM Hasselt Univ. residues Determination of dead-layer 13-14 Hasselt Univ. variation in a HPGe detector Investigation of rare alpha and References 22-14 beta decays and search for Inst. for Nuclear Research, Kiev double beta decay at HADES 1. EURATOM Treaty: Consolidated version of the Investigation of the half-live of Treaty establishing the European Atomic Energy 21-14 180mTa, Nature's most long-lived Techn. Univ. Dresden Community. http://eur-lex.europa.eu/legal- isomeric state Ultra low-level measurements of content/EN/TXT/?uri=CELEX%3A12012A%2FTX 8-15 WHOIb radiocesium in Pacific sea water T (2012). Measurement of attenuation 2. W. Bambynek, Precise solid angle counting. 9-15 coefficients of Geopolymers with Hasselt Univ. Proceedings from symposium on standardization of NORM residue radionuclides 10-14 October 1966, International Inst. for Nucl. Measurement of fluxes of Atomic Energy Agency, p. 373, 1967. 11-15 charged particles escaping Phys. Hungarian Acad. Science, fusion plasmas at KSTAR 3. M. F. L'Annunziata (Ed.), Handbook of Debrecen rd Gamma-ray spectrometry Radioactivity Analysis. P. 894. 3 Edition, 2012. analysis of NORM residues that Academic Press. 12-15 Hasselt Univ. are candidates for inclusion in 4. W. Bambynek et al., X-ray Fluorescence Yields, construction materials Auger, and Coster-Kronig Transition Probabilitie. Development and testing of inorganic polymers for Review of Modern Physics 44(4), 1972. 17-15 construction materials using Hasselt Univ. 5. W. Bambynek et al., Orbital Electron Capture by NORM-residue (slag) from a the Nucleus. Review of Modern Physics 49, 1977. novel source in Belgium 6. A.J. Fenwick, K.M. Ferreira and S.M. Collins. Radiological characterisation in 109 KU Leuven + Measurement of the Cd half-life. Appl. Radiat. 01-16 a metal recovery process from UHasselt bauxite residue (red mud) Isot. 109, 2016 pp.151-153. Analysis of low level 137Cs and 7. M-M. Bé et al.. Table of Radionuclides 03-16 134Cs concentrations in rice plant SCK•CEN, Mol Vol.8.Bureacu international des Poids et Mesures samples 2016. Comments to the evaluation available at Pulse shape characterisation of 15-16 MPI-K, a SAGe well-detector Heidelberg http://www.nucleide.org/DDEP_WG/Nuclides/Cd- Radiological characterisation of 109_com.pdf 13-16 geopolymers produced using Uhasselt 8 M. Hoshi, Private Communication, 19 July, 2012. NORM residue. 9 J. Gasparro, M. Hult; G. Marissens, M. Hoshi, K. Benchmarking of particle probes 17-16 Demokritos, Athens Tanaka, S. Endo, M. Laubenstein, H. Dombrowski, for fusion research 60 Ultra low-level measurements of D. Arnold. Measurements of Co in massive steel 20-16 Ra-isotopes and radiocesium in WHOI samples exposed to the Hiroshima atomic bomb Pacific sea water samples explosion. Health Physics Journal: 102(4), 2012 pp. Search for double beta decays Carleton 02-17 * University, 400–409. doi: 10.1097/HP.0b013e31823a172e. in cerium Ottawa 10 S. Pommé et al. Evidence against solar influence on Age determination of seasonal Swedish nuclear decay constants. Phys. Rev Lett. 761, 03-17 coral layers by measuring low- Radiation Safety (2016), pp. 281–28. level natural radioactivity Authority Study of hydrothermal plumes in 11 G. Lutter, M. Hult, G. Marissens, H. Stroh, F. Tzika. 06-17 * the Southern Pacific Ocean WHOI A gamma-ray spectrometry analysis software using isotopic fingerprints. environment. Appl. Radiat. Isot., In press. Measurement of fluxes of Inst. for Nucl. doi.org/10.1016/j.apradiso.2017.06.045 charged particles escaping H- 12-17 Phys. Hungarian mode fusion plasmas generated Acad. Science, by KSTAR - 2017 Debrecen Gamma-ray emitters in Inst. of Nucl. 13-17 * biological samples from Phys. Polish Acad. of Sci., Antarctic Warzaw *Conditional approval b WHOI = Woods Hole Oceanographic Institute, USA. 5

Importance of underground laboratories for science and technology

Aldo Ianni1,*

1 Laboratorio Subterraneo de Canfranc, Paseo de los Ayerbe S/N, 22880 Canfranc Estacion Huesca, Spain

1 Introduction water or solid and liquid scintillators, for removing impurities such as 85Kr and 39Ar from nitrogen, xenon, Deep Underground Laboratories (DULs) are research and argon, for reaching sensitivities in the range of 1-10 infrastructure built underground with an overburden of µBq/kg in radioactivity screening, for supporting the more than 1000 meters-water-equivalent. This shielding development of high sensitivity and low background reduces by a large factor the flux of cosmic rays. There light sensors, for improving performances of liquid are 13 DULs deployed in 12 Countries in the north scintillators based on noble gases. hemisphere [1]. Some DULs have been in operation for In this paper some examples of ancillary facilities in about 50 years. A number of crucial new technologies DULs and new technologies are discussed in more have been developed in DULs to support the search for details. rare events. Two Nobel prices have been awarded to research activities carried out in DULs in 2002 and 2015. Three new DULs are proposed, two in the south 2 Common facilities in DULs hemisphere. DULs in the south hemisphere will offer an important complementarity because of the difference in In order to discuss common facilities in operation in the annual modulation of cosmic rays. In Fig. 1 we show DULs to support experimental research we take as an the muons flux from cosmic rays in DULs. example the layout of the Astroparticle Research Facility DULs are multidisciplinary infrastructures to carry out (ARF) under construction in South Korea in an iron research on rare events, such as proton decay, neutrino mine. This new infrastructure should be functioning in interactions, and dark matter, on geophysics, and on 2018-2019. The layout is based on the long tradition biology in extreme environments. developed over many years in other DULs. In Fig. 2 we A number of DULs are excavated in a mine environment show the layout of ARF. and have access through a shaft or an inclined driving way. Others are excavated on purpose by train or road tunnels. In this latter case the access is horizontal. At present the total excavated volume for DULs is about 106 m3 [1]. Radon is a main concern in underground. In order to comply with restrictions imposed by national and international regulations a forced ventilation is at work in all DULs. The air change per days in DULs goes from a few to about 40 times the excavated volume. This reduces the radon activity, which in the worst case is about 300 Bq/m3. The Boulby DUL is an exception because is excavated in a salt and potash mine. In Boulby the radon natural activity is only a few Bq/m3. To carry out research on rare events in DULs a number of facilities have been developed. In addition, experiments in DULs have developed new technologies in a number of fields. In particular, we mention Fig.1. Muons flux from cosmic rays in DULs. techniques developed for reducing the radioactivity in

* Corresponding author: [email protected] 6

The main research activity in ARF will be the direct References search for dark matter and for neutrinoless double beta decay. To properly exploit this research activity a 1. A. Ianni, Int. J. Mod. Phys A 32, 1743001 (2017). number of facilities are essential. In particular, the new 2. M. Wojcik and G. Zuzel, Int. J. Mod. Phys. A 32, DUL design foresees: (1) a radon abatement system and 1743004 (2017). (2) a radon-free clean room, (3) a radioactivity screening 3. M. Giammarchi, Int. J. Mod. Phys. A 32, 1743011 laboratory, equipped with low background germanium (2017). detectors, (4) a water purification plant, (5) an electro- 4. forming set-up, and (6) a crystal growing laboratory. More specific ancillary facilities can be added to the previous ones. In the following we discuss the use and features of these facilities.

Electrical room Crystal growing room Network room (1F, 70m2) lounge Machine shop (2F, 70m2)

HPGe Electroform copper Clean room storage(1F, 100m2) 2 (1F, 70m2) (2F, 100m ) (1F, 200m2) Electrical room (1F) Lounge (2F)

Water shielding control room φ ank ( 10m) 2 (2F, 50+50m ) Gas station (2F) Test rooms Rn free air sys. (1F) (1F, 50+50m2)

Fig.2. Layout of ARF. See text for details.

A radon abatement system makes radon-free air by using low temperature charcoal filters. The system can produce as much as 200 m3/h or more. The radon in the air produced is at the level of mBq/m3. A sensitive radon detector is needed to measure such a low radon level. This detector has been developed and deployed at Gran Sasso in Italy and Canfranc in Spain [2].Similar detectors will be deployed in other DULs. The radon- free air can be used as a make-up air unit for a clean room. A radon-free clean room is a new infrastructure conceived for assembling of detectors components reducing plate out of radon daughters, such as 210Pb and/or 210Po. These radioactive isotopes will produce surface background, which limits the sensitivity to search for rare events. Radioactivity screening is crucial in DULs to select ultra radio-pure materials, which are used to make detectors components. In DULs high purity germanium detectors (HPGe) are used for this purpose. A gamma spectroscopy screening facility is commonly operated in DULs. All around DULs there are some 70 HPGe detectors serving this important work. Collaborations between DULs help putting forward huge screening campaigns. A water Cherenkov detector can serve as active veto against cosmic muons in underground and as a passive veto against neutrons (radiogenic or cosmogenic). Therefore, an apparatus installed inside an instrumented water tank will be screened against environmental and cosmic radiation. However, the radio-purity of the water must be reduced. For this reason water purification systems are often installed in DULs [3].

7

Search for rare decays in nuclear physics

V.I. Tretyak*

Institute for Nuclear Research, 03028 Kyiv, Ukraine

Introduction hierarchy. Because in many theories lepton number L is related to baryon number B (e.g., only B–L is conserved Nuclear physics exists already more than 100 years, but but not B and L individually), violation of L in new nuclear decays are still discovered. Improvements in neutrinoless 2β decay could explain why we observe experimental techniques and super-low background only matter around and no antimatter in equal quantities. measurements deep underground allowed to observe Few examples of big experiments to study 2β during last years extremely rare double beta, single beta decays will be given. and alpha decays of atomic nuclei. 2 Rare single beta and alpha decays 1 Investigations of double beta decays Measurements performed deep underground to There are 35 nuclides present in natural isotopic mixture suppress backgrounds from cosmic muons and use of of elements, for which single beta decay (A,Z) → extremely pure in radioactive sense materials allowed to − (A,Z+1) + β + νe is forbidden (or strongly suppressed improve experimental sensitivity and to observe at the due to big change in spin and parity), but process with first time rare beta decays with half-lives ~1015 years. simultaneous emission of two electrons (A,Z) → One of the examples is β decay of 115In to the first − 115 (A,Z+2) + 2β + 2νe is allowed. Similar processes with excited level of Sn with the lowest ever measured Qβ emission of two positrons, or one positron with capture value of 155 ± 24 eV. Alpha decays of 151Eu, 180W, 190Pt, 209 18 21 of one atomic shell electron, or capture of two electrons Bi with T1/2 in the range of 10 – 10 were also are possible for 34 nuclides [1]. Such decay was recently observed. Few interesting studies of rare β and considered at the first time in 1935 [2], experimental α decays will be reviewed. searches for 2β decays started in 1948 [3], and the first firm laboratory observation was achieved in 1987 [4], 52 years after paper [2]. This is exactly double time which 3 Search for disappearance of matter mankind spent to observe elusive particle neutrino, from (nucleons and electrons) hypothesis of Pauli in 1930 [5] to the first observation in 1956 [6]. To-date processes with simultaneous emission Nuclear physics methods give a possibility to search for of 2 electrons and 2 neutrinos are observed for 11 disappearance of protons, neutrons and electrons testing nuclides with half-lives in the range of 1018 – 1024 years, in this way laws of conservation of electric charge and and, while only 36 events were detected in the first baryon number. Half-life limits for these processe were 23 30 observation [4], up to ~106 events are registered now in improved last time from ~10 to ~10 years. the most productive current experiments like NEMO-3 or GERDA. − References The two neutrino process (A,Z+2) + 2β + 2νe is a usual (but very rare) process which does not forbid any 1. V.I. Tretyak, Yu.G. Zdesenko, At. Data Nucl. Data conservation law and is allowed in the Standard Model Tables 61, 43 (1995); 80, 83 (2002). (SM). Many theories, which consider SM as only low 2. M. Goeppert-Mayer, Phys. Rev. 48, 512 (1935). energy approximation, predict existence of neutrinoless 3. E. Fireman, Phys. Rev. 74, 1238 (1948). − process (A,Z+2) + 2β which can occur if neutrino is a 4. S.R. Elliott et al., Phys. Rev. Lett. 59, 2020 (1987). Majorana particle (equal to its antiparticle) with non- 5. W. Pauli, Letter to Phys. Congress in Tubingen zero mass. Neutrinoless 2β decay is of the great interest 4.12.1930. because it can clarify neutrino nature (Majorana or 6. C.L. Cowan jr. et al., Science 124, 103 (1956). Dirac), absolute scale of neutrino masses and their

* Corresponding author:[email protected] 8

The Importance of Rare Nuclear Decays

Björn Lehnert Carleton University, Department of Physics, 1125 Colonel By Drive, Ottawa, Canada

1 Introduction Model. Observing such a decay would imply lepton number violation and the Majorana nature of the The study of nuclear decays has often brought deep neutrino which ultimately sheds light on the insight into the field of particle and nuclear physics in understanding of the matter – antimatter asymmetry in the past. The continuous nature of the beta decay the Universe through leptongenesis. In addition, the spectrum lead Wolfgang Paul to postulate the neutrino in neutrino mass can be constrained which would help to 1930. Subsequently, beta decays lead to the formulation determine the neutrino mass hierarchy and ultimately of the theory for weak interactions by Enrico Fermi in leads to the better understanding of cosmology itself. 1933 which is generically valid for all other low energy weak interactions. Later in 1956 Chien-Shiung Wu used The measured half-lives of 0νββ decays are connected beta decays of a 60Co source to show that the with the neutrino mass via nuclear matrix elements conservation of parity was violated for weak which need to be theoretically determined using nuclear interactions. And just one year later Goldhaber could models. These calculations are notoriously difficult and demonstrate the helicity of the neutrino with beta decays one of the largest uncertainty in the sensitivity for 0nbb of a 152mEu source. decay experiments. However, auxiliary measurements can help to improve these calculations with observing The investigation of new physics with nuclear decays is the well-known two-neutrino double beta (2νββ) decay significantly more challenging today. However, even which has been measured in 11 nuclides with half-lives today, nuclear decays are used as one of the most of 1018 to 1024 yr. These are the rarest nuclear decays sensitive tools to probe beyond the Standard Model of observed to-date. Especially the observation of two particle physics. The neutrino mass is being measured by different transitions (into the ground state and excited precisely looking at the endpoints of low energy beta states) in the same isotope can test and constrain decays such as 3H and 187Re and searches for effective parameters in the nuclear models. This neutrinoless double beta decay in many different specifically helps the search for 0νββ decays but also isotopes are used to determine if the neutrino is its own adds generic knowledge to the understanding of nuclear anti-particle and can potentially lead to an explanation physics such as the quenching of the axial-vector for leptongenesis. coupling in nuclear matter.

These searches can be broadly separated into (1) In this presentation I will briefly outline the importance precision measurement of abundant nuclear decays and of 0νββ decay searches and show examples for the (2) investigation of extremely rare nuclear decays. In this measurement of 2νββ decays with gamma spectroscopy. presentation I will focus on rare nuclear decays, discussing their implications for particle physics beyond the Standard Model, for the general understanding of 3 Understanding Nuclear Structure nuclear structure and their application in other research Apart from 2νββ decays, also rare beta decays are of fields in the form of nuclear chronometers and interest for understanding the nuclear structure. Most understanding radioactive backgrounds. beta decays are allowed or single forbidden having a relatively well understood spectral shape and a short 2 Searches for Physics Beyond the half-life. However, a few beta decay isotopes can only Standard Model decay via forbidden transitions which distorts their spectral shape and makes these decays sensitive to After its vital role of understanding weak interactions poorly known nuclear physics parameters such as the and neutrinos in the past, the interest of beta decays has vector and axial vector couplings in nuclei. The highest 50 mainly shifted to double beta decays which are second forbidden beta decays are 4-fold forbidden such as V, 113 115 order processes and thus very rare. Neutrinoless double Cd and In. Apart from these, a very interesting case 180m beta (0νββ) decay searches are one of the main is Ta which – in addition of having a very long half- approaches to search for physics beyond the Standard life by itself – is the longest lived isomeric state and also

* Corresponding author: [email protected] 9

the rarest naturally occurring isotope that is known. In this presentation I will discuss a recent search for 180mTa decays within the EUFRAT framework.

4 Application in Other Research Fields

Rare nuclear decays have also applications in other fields of research. Isotopes with half-lives on geological or cosmological timescales can be used as nuclear chronometers. Precision half-life measurements of these isotopes helps to reduce uncertainties for dating geological or cosmological objects.

For low-background astroparticle physics experiments such as e.g. dark matter searches, understanding the lowest background components is crucial. Even rare nuclear decays can pose a background threat. In the end of this talk I will quickly outline recent measurements of rare nuclear alpha and beta decays applicable for other fields of research.

10

Developments and future plans for large scale double beta decay experiments

Andrea Kirsch1,* on behalf of the GERDA Collaboration

1 Max-Planck-Institut für Kernphysik, Heidelberg, Germany

1 Motivation 2 Overview Apart from its overwhelming success, the Standard The talk reviews the motivation for the search of Model of particle physics still lacks an explanation for neutrinoless double beta decay, as well as the main several observed phenomena, such as the origin of the principles of current projects in this field (with special (tiny) neutrino mass or the nature of the dark energy. It emphasis on the GERDA (GERmanium Detector Array) fails to find a suitable dark matter candidate and yet it + KamLAND-Zen Experiments [5,6]). A proposal for an can also not explain one of the most puzzling aspects of envisaged next-generation large-scale programme will cosmology: the dominance of matter over antimatter. be discussed. Also an overview of recent research Hence a new mechanism has to be responsible. Lepton activities @ the HADES underground laboratory (as part number violation, however, might be the key to of the EUFRAT) for the development of a novel detector understand the baryon asymmetry in our Universe [1]. design with enhanced background suppression performance is given. In most theoretical extensions of the Standard Model [2,3,4], neutrinos are assumed to be their own antiparticles. This would directly imply the existence of neutrinoless double-beta (0νββ) decay, where a nucleus References of mass number A and charge Z decays as (A,Z) → - 1. S. Davidson, E. Nardi & Y. Nir, “Leptogenesis”, (A,Z+2) + 2e and lepton number is indeed violated. Phys. Rep. 466, 105-177 (2008). 2. R. N. Mohapatra & A. Y. Smirnov, “Neutrino mass Despite several current (and past) experimental attempts 76 130 136 and new physics”, Annu. Rev. Nucl. Part. Sci. 56, using, for example, the Ge, Te and Xe isotope, 569-628 (2006). this extremely rare second-order process has not been 3. R. N. Mohapatra et al., “Theory of neutrinos: a unambiguously observed so far. As different as the white paper”, Rep. Prog. Phys. 70, 1757-1867 detection principles and hardware setups of this various (2007). research projects are, one thing they do have in common: 4. H. Päs & W. Rodejohann, “Neurinoless double beta all of them measure the sum of the electron energies decay”, New J. Phys. 17, 115010 (2015). released in the decay, which corresponds to the mass 5. M. Agostini et al., “Background-free search for difference Qββ of the two nuclei, as experimental neutrinoless double-β decay of 76Ge with GERDA”, signature. Nature 544, 47 (2017).

6. A. Gando et al., “Search for Majorana neutrinos Up to now, the obtained results have shown that the near the inverted mass hierarchy region with νββ 0 decay half-life is at least 15 orders of magnitude KamLAND-Zen”, Phys. Rev. Lett. 117, 082503 longer than the age of the Universe. This already sets a (2016). fundamental benchmark on the challenges of future double-beta decay experiments: In order to not only increase the experimental sensitivity, but also to allow for an actual discovery potential, the utmost background suppression is required.

* Corresponding author: [email protected] 11

Towards a sustainable society by adequate measures to reduce impact of NORM

1* 1 1,2 3 3 3 3 Wouter Schroeyers , Tom Croymans , Zoltan Sas , Guillaume Lutter , Gerd Marissens , Heiko Stroh , Mikael Hult , Gergo Bator4, Rosabianca Trevisi5, Cristina Nuccetelli6,Federica Leonardi5, Tibor Kovacs4, Sonja Schreurs1

1 Hasselt University, CMK, NuTeC, Nuclear Technology - Faculty of Engineering Technology, Agoralaan building H, B-3590 Diepenbeek, Belgium

2School of Natural and Built Environment, Queen’s University Belfast, David Keir Bldg., 39-123 Stranmillis Rd, Belfast BT9 5AG, United Kingdom

3 JRC-Geel, Retieseweg 111, 2440 Geel, Belgium

4University of Pannonia, Institute of Radiochemistry and Radioecology, H-8200, Egyetem St. 10., d Veszprém, Hungary

5 INAIL (National Institute for Insurance against Accidents at Work)- Research Sector, DiMEILA, Via di Fontana Candida 1 00078 Monteporzio Catone (Rome), Italy

6ISS (National Institute of Health), Technology and Health

1 Introduction 2 Objective

Enhanced concentrations of natural occurring nuclides The COST Action Tu1301 NORM4Building (2014- (NORs) are present in slag and bottom ash from coal- 2017) initiated new research on the radiological fired power plants, phosphorous slag from thermal evaluation of construction material that are currently in phosphorus production, unprocessed slag from primary the research stage. The most important objective of the iron production and lead, copper and tin slags from COST action Tu1301 ‘NORM4Building’ is the exchange primary and secondary production. The relative of multidisciplinary knowledge and experience concentrations of NORs depend on the origin of the ores th (radiological, technical, economical, legislative, and the used industrial process [1]. On the 5 of ecological) to assure safe reuse of NORM residues in December 2013, the Council of the European Union has new tailor-made sustainable building materials adopted the new Directive 2013/59/EURATOM considering the impact on both external gamma exposure (Euratom Basic Safety Standards, EU-BSS) [2] Several of the building occupants and indoor air quality. of the mentioned residues have very interesting properties for the cement & concrete industry as alternative raw materials, supplementary cementitious For the radiological evaluation of practises a close materials, alternative fuel or aggregates [3, 4, 5]. In collaboration was established with the METRONORM particular in new types of cement and concrete based on project and several EUFRAT projects were undertaken Alkali-Activated Material (AAM) a relatively large that meet both the goals of NORM4Building and fraction of residues could be used [6]. In the ceramic METRONORM projects. industries slags from various types of metal smelting can be used as aggregates in or in the bond system of clay- 3 Results and output based ceramics [7]. For safe use of by-products from a radiological point of view, the EU-BSS requires a radiological screening and further characterisation of In the course of the NORM4Building project a building materials that incorporate specific residues from radiological database on NORM & building materials industries that process NORM (Naturally Occurring was developed. The NORM4Building database is radioactive materials) considered are among others fly available via www.norm4building.org and in the future ash, phosphogypsum, phosphorus, tin and copper slag, via the website of the new European NORM Association red mud and residues from steel production, before the (ENA). In addition, new measurement protocols and they can be distributed on the market. The assessment of dosimetrical tools were developed for a more accurate the impact of the EU-BSS on the reuse of NORM in new radiological evaluation of the use of NORM in types of construction materials is the main topic of the construction. The new dosimetric tools provide a more current contribution. realistic radiological screening of the reuse of building materials in addition to the Activity Concentration Index (ACI) that is proposed by the EU-BSS as screening tool.

* Corresponding author: [email protected] 12

In the provided presentation, the impact of the new EU- BSS on reuse of by-products in construction is assessed. The discussion will assess the relation sustainability and radiological aspects of safety in reuse on the basis of the results and output from the COST Action NORM4Building. During the discussion focus is given to the results of collaboration between NORM4Building and METRONORM and the contribution of Eufrat projects to the obtained results.

Acknowledgements

The authors would like to acknowledge networking support by the COST Action TU1301. www.norm4building.org. This work was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska- Curie grant agreement No 701932. This work was supported by the European Commission within HORIZON2020 via the EURATOM project EUFRAT for transnational access.

References [1] Management of NORM residues, IAEA TecDoc series - publication 1712, International Atomic Energy Agency, Vienna, Austria (2013) [2] COUNCIL DIRECTIVE 2013/59/EURATOM of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom, Official Journal of the European Union (2014) [3] Guidelines on Co-processing Waste Materials in Cement Production, The GTZ-Holcim Public Private Partnership, Switzerland (2006) [4] Hasanbeigi, A., Lu, H., Williams, C., Price, L., International Best Practices for Pre-Processing and Co-Processing Municipal Solid Waste and Sewage Sludge in the Cement Industry, Ernest Orlando Lawrence Berkeley National Laboratory, USA, (2012) [5] Siddique, R., Khan, M. I., Supplementary Cementing Materials, Springer (2011) [6] Shi, C., Krivenko, P.V., Roy, D.M., Alkali- Activated Cements and Concretes, Taylor & Francis, Abingdon, UK (2006) [7] Pontikes, Y., Angelopoulos, G.N., Effect of firing atmosphere and soaking time on heavy clay ceramics with addition of Bayer’s process bauxite residue, Adv. Appl. Ceram., 108, 50-56 (2009)

13

Towards a sustainable and safe construction industry: a radiological assessment on the reuse of by-products in construction materials.

1 2 2 2 1 1* Tom Croymans , Guillaume Lutter , Gerd Marissens , Heiko Stroh , Sonja Schreurs , Wouter Schroeyers , and Mikael Hult2

1 NuTeC, CMK, Nuclear Technology - Faculty of Engineering Technology Hasselt University, Agoralaan building H, B-3590 Diepenbeek, Belgium

2 JRC-Geel, Retieseweg 111, 2440 Geel, Belgium

1. Introduction have superior properties over conventional construction materials. The chemical, physical and microstructural properties of the processed residues are crucial for the Naturally occurring radionuclides (NORs) are spread in final application. variable concentrations in the earth’s crust. Due to industrial processing of primary or secondary raw materials, NORs can concentrate or dilute in the In the development of AAMs for public use, the produced (by-) products (also called residue) [1]. In this radiological characteristics need to be properly work, industrial by-products are being used or addressed. This aspect is considered in the European investigated for use in the production of construction Basic Safety Standards (EU-BSS) (Council Directive materials. Examples of such by-products are 2013/59/Euratom) [3]. The EU-BSS introduces a metallurgical slags, bauxite residue, phosphogypsum, fly legislative framework and sets a dose criterion for and bottom ashes, etc. Due to their possible enrichment construction materials. An accurate assessment of the in NORs, these products are sometimes called NORM effective dose is therefore of utmost importance to assure (naturally occurring radioactive materials)-residuesa. In safe reuse of by-products in AAMs. this study we focused on the most common primordial NORs: i.e. 40K and radionuclides part of the 238U, 235U or 232 In this study, concretes containing different levels of Th decay chains. bauxite residue are radiologically characterized by means of gamma-ray spectrometry. Their usage as road Certain by-products have proven to be promising construction and as building material is evaluated in precursors in the development of construction materials terms of occupational and public exposure. Next, the via a novel process named alkali activation [2]. The slag output of an industrial facility was followed during process of alkali activation allows using high volumes of a one month-production period. The variation of NORs residues, consequently tackling the environmental in the facility is discussed and an assessment of its usage challenges of stockpiling or re-processing these residues. as building material is presented. In addition, the resulting alkali activated materials (AAMs) aim at substituting environmentally 2. Output burdensome conventional cement and concrete materials. The worldwide cement production in 2016 is estimated at around 4.2 billion tons [4]. The production of cement 2.1. EUFRAT project number 12-14: is a CO2 intensive (1 kg cement corresponds to 1 kg “Measurement strategy for Geopolymers with CO2) process contributing to 5-8 % of the total NORM residues” anthropogenic CO2-emission worldwide [6]. Cement and concrete production require the exploitation of natural In this project non-ferrous slags were measured. These resources. In case of alkali activated alternatives, life slags can be easily converted by means of alkali cycle analyses show that the CO reduction varies 2 activation to geopolymers or inorganic polymers (both of between 30 and 80 % in comparison to cement which are subgroups of alkali activated materials) which production [7]. It is also been shown that AAMs can solely consist of slag [4]. Consequently, the results can be framed in a broader context linked to geopolymers. a IAEA has recommended not to use the expression TE- NORM (Technologically Enhanced NORM).

* Corresponding author: [email protected] 14

The industrial processes, in which the by-products, containing natural occurring radionuclides, are produced, 238U decay series are often complex and total monitoring can be challenging especially when the origin of the used raw 200 materials varies. In this study the NORs present in non- 180 ferrous fayalite slags of a secondary smelter facility, a 160 NORM-processing industry according to the EU-BSS, 140 were monitored daily during a one-month production 120 period. The survey involved the gamma-ray 100 spectrometric analysis of the decay products from the 80 238U and 232Th decay chains, 235U and 40K using HPGe 60 detectors. Secular equilibrium was observed for the slags 40 in the 232Th decay chain (fig.5.), in contrast to the 238U 20 decay chain (fig.6.). During the month in question the 0 ratios of maximum over minimum activity concentration Activity concentration (Bq/kg) 1 3 5 7 9 1113151719212325272931 were 4.5 ± 0.6 for 228Ra (fig.5.), 4.7 ± 0.7 for 228Th (fig.5.), 4 ± 1 for 238U (fig.6.), 6 ± 1 for 226Ra (fig.6.), 13 238U 226Ra 210Pb ± 7 for 210Pb (fig.6.) and 3.1 ± 0.5 for 40K (fig.7.) for the slags. None of the slag samples exceeded the exemption/clearance levels of the EU-BSS and RP-122 Fig.6. Activity concentration of 31 slag samples for the 238U part II, which can respectively provide guidance under decay series (coverage factor, k=2). Samples were collected at equilibrium and in absence of equilibrium [5]. As each 31 consecutive days of slag production. From [6]. NORM-processing industry has its own complexity and variability, the observed variations point out that one It also points to the benefits of NORM (-processing) should approach one-time measurements or low industries having access to modern radiological survey frequency monitoring methods cautiously. Low equipment like HPGe-detectors for daily controls. This frequency measurements should be optimized depending was also addressed in the European project on the discharge of the batches. A follow up of the MetroNORM, in which Lutter et al. [7] adopted a HPGe- industrial process and its output can provide important detector system for the same secondary smelter. At insights to assure a limited public exposure upon present most NORM (-processing) industries have to application of these industrial residues. send samples for radiological analysis by external laboratories, which leads to delays in obtaining results and a reluctance of performing extensive sampling. 232Th decay series

40 100 K 100 80 80 60 60 40 40

20 20 0 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Activity Activity concentration (Bq/kg) 1 3 5 7 9 1113151719212325272931

228Ra 228Th Activity concentration (Bq/kg) 40K

40 Fig.5. Activity concentration of 31 slag samples for the 232Th Fig.7. Activity concentration of slag 1 – slag 31 for K decay series (coverage factor, k=2). Samples were collected at (coverage factor, k=2). Samples were collected at 31 31 consecutive days of slag production. From [6]. consecutive days of slag production. From [6]. EUFRAT project number 12-14 led to two publications: [6] and [7].

15

2.2. EUFRAT project number 12-15: “Gamma- ray spectrometry analysis of NORM residues that are candidates for inclusion in construction materials” This EUFRAT project focusses on bauxite residue (red mud), which is a by-product of the aluminium industry. Reuse options of bauxite residue are very limited and it is estimated that over 2.7 billion tonnes of bauxite residue are currently stored [8].

The massic activity (here defined in accordance to the EU-BSS as activity concentration) of radionuclides from 238 232 40 the U, Th decay series and K were determined for concrete mixture samples incorporating 30, 40, 50, 60, 75, 85 and 90 % (by mass) of bauxite residue using Fig.2. Activity concentration index for streets and playgrounds gamma-ray spectrometry with a high-purity germanium for different bauxite concrete mixtures with different % (by detector. The studied bauxite residue can, from a mass) of bauxite residue incorporation. Blue spheres represent radiological point of view using activity concentration the P-series, red squares represent the C-series (k=2). Red line indexes developed by Markkanen [9], be used in indicates threshold value of 1. From [10]. concrete for building materials and in streets and playgrounds (road construction), even in percentages reaching 90 % (by mass) (fig.1. and fig.2.). However, when also occupational exposure is considered, an incorporation up to 60 % (by mass) (fig.3.) of Ukrainian bauxite residue for the construction of buildings allows the dose to workers below the dose criterion used by Radiation Protection (RP-) 122 (0.3 mSv/a) [5]. Considering RP-122 for evaluation of the total effective dose to workers no restrictions are required for the use of the Ukrainian bauxite residue in road construction (fig.4.).

Fig.3. Total effective dose for workers active in building construction in function of the different bauxite concrete mixtures with different % (by mass) of bauxite residue incorporation. Blue spheres represent P-series, red squares represent C-series. The red line indicates the dose criterion of 0.3 mSv/a proposed by RP-122. From [10].

Fig.1. Activity concentration index for building materials for different bauxite concrete mixtures with different % (per mass) of bauxite residue incorporation. Blue spheres represent the P- series, red squares represent C-series (k=2). Red line indicates threshold value of 1. From [10].

Fig.4. Total effective dose of workers active in road construction in function of the different bauxite concrete mixtures with different wt.% of bauxite residue incorporation. Blue spheres represent the P-series, red squares represent the C-series. The red line indicates the dose criterion of 0.3 mSv/a proposed by RP-122. From [10]. 16

Kovalchuk, A. Pasko, M. Hult, G. Marissens, G. EUFRAT project number 12-15 led to two publications: Lutter, S. Schreurs, Radiological characterization [10] and [11]. and evaluation of high volume bauxite residue alkali activated concretes, J. Environ. Radioact. 168 (2017) 21–29. doi:10.1016/j.jenvrad.2016.08.013. [11] P. Krivenko, O. Kovalchuk, A. Pasko, T. Acknowledgements Croymans, M. Hult, G. Lutter, N. Vandevenne, S. Schreurs, W. Schroeyers, Development of Special thanks to Danny De Smet, Mark Van Noyen, alkali activated cements and concrete mixture Eddy Pauwels and Stephaan Cauwbergs. design with high volumes of red mud, Constr. Build. Mater. 151 (2017) 819–826.

References [1] W. Schroeyers, Naturally Occurring Radioactive Materials in Construction Integrating Radiation Protection in Reuse (COST Action Tu1301 NORM4BUILDING), 1st ed., Woodhead Publishing, 2017. [2] J.L. Provis, Alkali Activated Materials State-of- the-Art Report, RILEM TC 224-AAM, 1st ed., Springer Dordrecht Heidelberg New York London, 2014. doi:10.1007/978-94-007-7672-2. [3] European Commission, Laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom, Off. J. Eur. Union. (2014) 1– 73. [4] L. Kriskova, P.T. Jones, H. Jannsen, B. Blanpain, Y. Pontikes, Synthesis and Characterisation of Porous Inorganic Polymers from Fayalite Slag., Slag Valoris. Symp. Zero Waste. 4 (2015) 227–230. [5] European Commission, Radiation protection 122 practical use of the concepts of clearance and exemption Part II application of the concetps of exemption and clearance to natural radiation sources, 2002. [6] T. Croymans, I. Schreurs, M. Hult, G. Marissens, H. Stroh, G. Lutter, S. Schreurs, W. Schroeyers, Variation of natural radionuclides in non-ferrous fayalite slags during a one-month production period, J. Environ. Radioact. 172 (2017) 63–73. doi:10.1016/j.jenvrad.2017.03.004. [7] G. Lutter, I.V. Schreurs, T. Croymans, W. Schroeyers, S. Schreurs, M. Hult, G. Marissens, H. Stroh, F. Tzika, A low-energy set-up for gamma-ray spectrometry of NORM tailored to the needs of a secondary smelting facility, Appl. Radiat. Isot. (2017) 1–5. doi:10.1016/j.apradiso.2016.12.048. [8] C. Klauber, M. Gräfe, G. Power, Review of Bauxite Residue “ Re-use ” Options, (2009). [9] M. Markkanen, Radiation Dose Assessments for Materials with Elevated Natural Radioactivity, Finish Cent. Radiat. Nucl. Safety. Rep. STUK- B-STO 32. (1995) 1–41. [10] T. Croymans, W. Schroeyers, P. Krivenko, O. 17

Counting of activation detectors at ultra-low level background facilities: Measurement of fluxes of charged particles escaping fusion plasmas at KSTAR

András Fenyvesi1,*, Mikael Hult2, Faidra Tzika2, Iulian Bandac3, Detlev Degering4, Aldo Ianni3,5, Matthias Laubenstein5, Anne de Vismes-Ott6, Gerd Marissens2, Heiko Stroh2, Guillaume Lutter2,Soohyun Son7, Suk-Ho Hong7, Jun Young Kim7, Junghee Kim7, Mun Seung Cheon7, Jungmin Jo8, Mihály Braun1, József Németh9, Sándor Zoletnik9 and Georges Bonheure10

1 Institute for Nuclear Research (MTA Atomki), Hungarian Academy of Sciences, Bem tér 18/c, H-4026 Debrecen, Hungary

2 EC, JRC-Geel, Retieseweg 111, 2440 Geel, Belgium

3 Laboratorio Subterráneo de Canfranc, Paseo de los Ayerbe S/N 22880 Canfranc Estacion, Huesca, Spain

4 VKTA – Strahlenschutz, Analytik & Entsorgung Rossendorf e. V., P.O. Box 510119, 01314 Dresden, Germany

5 INFN, Laboratori Nazionali del Gran Sasso, Via G. Acitelli 22, I-67100 Assergi (AQ), Italy

6 IRSN, Environnement Radioactivity Measurement Laboratory, Bât. 501, Rue du Belvédère, 91400 Orsay, France

7 KSTAR, National Fusion Research Institute, 169-148 Gwahak-ro, Yuseong-gu, Daejeon 34133, Republic of Korea

8 Department of Nuclear Engineering, Seoul National University, Seoul, Republic of Korea

9 WIGNER Research Centre for Physics (MTA Wigner RCP), Hungarian Academy of Sciences, Konkoly-Thege Miklós út 29-33, H- 1121 Budapest, Hungary

10 EC, DG RTD, 1000 Brussels, Belgium

1 Introduction Measurement of fluxes of the escaping ions needs probes that are capable of operation close to the edge of the Controlled fusion burn in future thermonuclear fusion plasma. reactors will rely upon the confinement of the energetic charged ions that play dominant role in heating the Besides several other techniques the activation probe plasma. Therefore, it is important to measure the fluxes method has been proposed [1] for detecting escaping of the energetic fast ions that escape the plasma. charged particles via the nuclear activation they induce in activation samples made of special materials. The Fast ions are produced in the fusion reactions like technique was installed first at the JET and later at the TEXTOR tokamak [2]. The method has been proposed D + D → p (3.024 MeV) + T(1.008 MeV) as a diagnostics for ITER [3] The first tests in ITER-like D + D → n (2.45 MeV) + 3He (0.817 MeV) geometry [4] were done at ASDEX Upgrade tokamak. D + T → n (14.1 MeV) + α (3.6 MeV) D + 3He → p (14.68 MeV) + α (3.7 MeV) An activation probe technique [5] has been developed for the Korea Superconducting Tokamak Advanced In the case of Ion Cyclotron Range of Frequencies Research (KSTAR) at National Fusion Research Institute (ICRF) heated plasmas accelerated primary ions can also (NFRI, Daejeon, South Korea), too. The first in-vessel escape the plasma. experiments employing the activation probe were performed on 26 October 2015. The aim was measurement of fluxes of ions that escaped H-mode

* Corresponding author: [email protected] 18

plasmas of KSTAR. Many results of the experiment have been reported [6].

This work is an overview of the experiments and the counting of the activated samples within the frame of the EUFRAT Transnational Access of EU JRC IRMM Geel.

2 Experimental

2.1. The activation samples used at KSTAR The activation detectors (samples) were made of LiF, CaF2 and YVO4 materials with at least 99.99 w% nominal purity. One sample per material was taken for detailed elemental analysis via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The analysis was carried out at MTA Atomki. The results of the analysis proved the 99.99 w% purity of the LiF, CaF2 and YVO4 materials.

The outside dimensions of each sample were 11 mm x 10 mm x 2 mm. A 3-character ID code was engraved in the back (not exposed to plasma) side of each sample.

8 sets x 6 samples/set were prepared. Each set of samples consisted of two pcs of LiF, two pcs of CaF2 and two pcs of YVO4 samples. All chemical elements in the samples were of natural isotopic abundance. One set (Set-9), consisting of one pc of each material was used as blank. Set-9 was used for monitoring the contribution Fig.1. The LiF, YVO4 and CaF2 samples in the sample holder of the environmental radiation background. Set-9 was channels of the activation probe (a). The probe with the sample always kept together with sets 1–8 except the time while covered by the graphite shield (b). The probe installed on the sets 1–8 were in the vacuum vessel (torus) of KSTAR. port of the manipulator (c).

2.3. Exposition of the samples to ions escaping 2.2. The activation probe at KSTAR H-mode plasmas of KSTAR The activation probe developed for the mid-plane Each sample set was exposed to ions escaping high- manipulator of Port D of KSTAR was used in the confinement mode (H-mode) plasmas. The ID codes of experiments. Technical details of the rotating activation the sample sets and the ID codes of their relevant plasma probe and the multi-purpose manipulator have been shot are listed in Table 1. Set-2 and Set-3 were exposed published elsewhere [5]. to stable plasma shots with long flat top.

The LiF, YVO and CaF activation samples were placed 4 2 Table 1. The ID codes of the sample sets and the plasma shots. in the sample holder channels of the 8-stage rotating sample holder of the activation probe (Fig. 1a). Then the Sample set ID Plasma shot ID Duration probe with the sample sets was covered by a 4 mm thick graphite shield with a slit of dimensions 60 mm×6 mm Set-1 #014138 11.2 s (Fig. 1b). The assembled activation probe was installed Set-2 #014139 25.7 s on the end of the mid-plane manipulator of Port D of Set-3 #014140 27.1 s KSTAR (Fig. 1c). Set-4 #014141 9.2 s Before expositions the probe was kept in the parking Set-5 #014142 9.4 s position of the manipulator. During preparation for the 7.4 s requested plasma shot the sample set selected for Set-6 #014143 exposition was rotated under the slit of the graphite #014145 3.6 s Set-7 shield of the probe. Then the probe was moved #014146 3.5 s longitudinally close to the expected edge of the plasma. During the plasma discharge the end of the probe cover The detailed plasma physics data for each shot are stored was at ∼10 cm away from the Last Closed Flux Surface in and can be retrieved from the pulse based data archive (LCFS, the outer boundary of the plasma). of KSTAR managed and referenced by the shot number. 19

The experiments were carried out on 26 October 2015 and the last plasma shot was at 26/10/2015 9:20 UTC.

2.4. On-site counting of the activated samples Five hours after the end of the last shot a 9 h screening measurement was started using a HPGe gamma spectrometer. All samples were counted together to check the presence of short-lived radioisotopes and to obtain information on the feasibility of on-site counting individual samples in future experiments.

2.4. Off-site counting of the activated samples Fig. 2. 7Be activities measured for the LiF samples. JRC IRMM-Geel coordinated the off-site counting of the 48+3 samples and distributed them to low and ultra-low 7Be is products of the 7Li(p,n)7Be and the 6Li(3He,d)7Be background counting facilities of five laboratories of the nuclear reactions. Protons are products of the D(d,p)T CELLAR Collaboration. The off-site counting started 10 fusion reaction and the energy of the emitted proton is Ep days after the experiments at KSTAR and it was finished = 3.024 MeV. 3He is the product of the D(d,n)3He fusion on 15 March 2016. 3 reaction and He is emitted with E3He = 0.817 MeV energy. No measured cross section data was found for Details of the off-site counting of the samples at the the 6Li(3He,d)7Be reaction. Therefore, it was assumed different laboratories can be found in Ref. [6]. that the cross sections of the 6Li(3He,d)7Be reaction are significantly lower for E ≤ 0.817 MeV than the cross The comparability among the CELLAR laboratories was 3He section of the 7Li(p,n)7Be reaction at Ep ≤ 3.024 MeV checked by conducting a round robin exercise, using a 6 nat energies. The abundance of Li in Li is 7.59%. Thus, it sample prepared at JRC as to approach the geometry of 7 7 was assumed that the Li(p,n) Be nuclear reaction the KSTAR activation samples. The sample material was 7 induced by the escaping protons dominated the Be Monazite sand of mass 0.7337 g. Further details of the 7 production in the LiF samples. First the Be activity exercise can be found in Ref. [6]. 7 7 produced via the Li(p,n) Be reaction was calculated for -2 Φp = 1 cm proton fluence. The energy loss of the 3 Results protons in LiF was taken into account in the calculations. The cross section data were taken from the EXFOR data Four gamma lines from four radioisotopes were base [7]. Finally, the calculated 7Be activity was adjusted identified in the gamma spectrum measured during the to the measured 7Be activities varying the proton flux. off-site screening of the samples (Table 2). The obtained fluxes of escaping protons were in the φ = 3.9 x 105 – 3.3 x 106 cm-2s-1 range depending on the shot. Table 2. The gamma lines and the isotopes identified in 51 during the on-site screening For the Cr activity of the YVO4 samples A(tref) = 1.2 mBq – 4.8 mBq activities were measured at very low Half life Gamma line Intensity Isotope statistics [6]. The activities were shot dependent with (T1/2) (Eγ; keV) (Iγ; %) weak significance. The possible activation process is the 7 51 51 Be 53.3 d 477.6 10.5% V(p,n) Cr reaction. The results suggest that the YVO4 45Ti 3.08 h 720.2 0.154% samples detected escaping protons. The measured 51Cr 27.7 d 320.1 10% activities were not used for estimation of the proton flux. 90mY 3.19 h 479.2 90.7%

The three non-irradiated samples (blank samples) were measured at HADES. The blank samples contained no detectable activation products [6].

On the basis of the off-site counting of the LiF samples 7 A(tref) = 27 mBq - 188 mBq Be activities were calculated (Fig. 2.) and there was strong correlation between the measured activity and the shot duration [6].

88 Fig. 3. Y activities measured for the YVO4 samples. 20

88 Y was also detected in each YVO4 sample (Fig. 3.). Acknowledgements Practically shot independent activities were measured in the A(tref) = (5.99 ± 0.53) mBq range [6]. The "ITPA TG-D JEX DIAG-5: Field test of an activation probe" was supported by the Diagnostics The YVO4 samples could be activated via the Topical Group (TG-D) of International Tokamak Physics 89Y(p,x)88Y, 89Y(d,x)88Y and the 89Y(n,2n)88Y nuclear Activity (ITPA). reactions. The emitted particles in the D(3He,p)4He reaction are Ep = 14.68 MeV protons and En = 14.1 MeV This work was supported by the EUFRAT open access neutrons in the T(d,n)4He fusion reactions. The work package of the European Commission's Joint interpretation of the measured 88Y activities needs Research Centre EURATOM programme under further analysis of the plasma physics data of the plasma Horizon2020 (EUFRAT Project No. 11–15, EC-JRC, shots. 2016).

The presence of 7Be was observed in the case of some This work has been carried out within the framework of 7 YVO4 samples. It can not be excluded that the Be atoms the EUROfusion Consortium and has received funding sputtered from the neighbouring LiF samples and from the Euratom research and training programme deposited on the YVO4 samples [8]. 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect In the case of the CaF2 samples no radionuclide resulting those of the European Commission. from charged particles or neutron activation was detected [6]. This research was supported by the Ministry of Science, ICT, and Future Planning, under KSTAR project (EN1601-7) and by the National Research Council of 4 Conclusions Science and Technology, under the International Collaboration & Research in Asian countries (No. The short-lived 45Ti (T = 184.8 m) can be induced via 1/2 PG1314). 42 3 γ 45 43 3 45 the Ca( He, ) Ti and the Ca( He,n) Ti reactions. Therefore, on-site counting of each CaF2 sample is 3 The authors thank the members of the KSTAR Team for recommend to enable estimation of the flux of He from their contribution to the experiments. DD fusion.

The YVO4 samples detected escaping protons via the References 51V(p,n)51Cr nuclear reaction but reliable estimation of the proton fluxes was not feasible.. 1. G. Bonheure, I. Lengar, B. Syme, E. Wieslander, M. Hult, J. Gasparro, G. Marissens, D. Arnold, M. Fluxes of protons escaping H-mode DD plasmas have Laubenstein, S. Popovichev, Review of Scientific been detected via the LiF samples. The estimated fluxes Instruments 79, 10E504 (2008). of escaping protons were in the φ = 3.9 x 105 – 3.3 x 106 2. J. Mlynar, G. Van Wassenhove, M. Hult, R. cm-2s-1 range depending on the shot. González de Orduña, G. Lutter, P. Vermaercke, A. Huber, B. Schweer, G. Esser, W. Biel, Review of The particle fluxes that can be obtained with the Scientific Instruments 83 10D318-3 (2012). activation probe technique are absolute quantities. The 3. G. Bonheure, G. Van Wassenhove, M. Hult, R. data can be used as reference data for plasma physics González de Orduña, D. Strivay, P. Vermaercke, T. transport calculations. Also, the activation probe Delvigne, G. Chene, R. Delhalle, A. Huber, B. technique can be used for calibration of other diagnostics Schweer, G. Esser, W. Biel, O. Neubauer, Fusion methods e.g. Fast Ion Loss Detector (FILD) that is based Engineering and Design 88, 533 (2013). on scintillating materials. This fact is very important 4. G. Bonheure, M. Hult, A. Fenyvesi, S. since FILD is the most preferred diagnostics option for Äkäslompolo, D. Carralero, D. Degering, A. De- ITER at present. Vismes Ott, M. Garcia-Munoz, B. Gmeiner, A. Herrmann, M. Laubenstein, L. Guillaume, J. A FILD is used at KSTAR, too. Furthermore, operation Mlynar, H. W. Mueller, V. Rohde, W. Suttrop, G. of an ex-vessel scintillating fiber neutron detector is also Tardini, Europhysics Conference Abstracts 37D no. planned. Thus, simultaneous measurements with these O6.510 p. 4. two methods and the activation probe technique seem to 5. S. H. Son, S. H. Hong, Junghee Kim, Jun Young be feasible. Kim, H. S. Kim, F. Ding, G. N. Luo, J. Németh, S. Zoletnik, A. Fenyvesi, R. Pitts, Fusion Engineering On the basis of the results of the present study further and Design 109–111 (Part A), 286–289 (2016). field tests of the activation technique at KSTAR has 6. F. Tzika, M. Hult, A. Fenyvesi, I. Bandac, D. been proposed to the Diagnostics Task Group of the Degering, A. Ianni, M. Laubenstein, A. de Vismes- ITER Tokamak Physics Activity (ITPA). Ott, G. Marissens, H. Stroh, G. Lutter, S. Son, S.-H. Hong, J. Y. Kim, J. Kim, M. S. Cheon, J. Jo, M. Braun, J. Németh, S. Zoletnik, G. Bonheure, 21

Applied Radiation and Isotopes 126, 121-126 (2017). 7. Experimental Nuclear Reaction Data (EXFOR) Database Version of 2017-09-04, Software Version of 2017-09-19, available on line at https://www-nds.iaea.org/exfor/exfor.htm 8. J. Gasparro, M. Hult, G. Bonheure, P. N. Johnston, Applied Radiation and Isotopes 64, 1130-1135 (2006).

22

Radium Isotopes as Tracers of Hydrothermal Activity in the Deep Ocean

Matthew A. Charette1,* and Lauren E. Kipp1

1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543

1 Introduction facility, as well as a similar lab in a mountain tunnel at Modane, France, we were able to quantify the activity of Since the discovery of hydrothermal venting in the deep this important Ra isotope in the plume at the EPR ocean in the mid 1970s, ocean scientists have been (Fig.1.). We will discuss this result as well as those from actively engaged in the study of the impact of this the MAR in the context of Ra isotopes utility as a tracer process on ocean elemental cycles. The high temperature of hydrothermal iron in the deep ocean. (~200-400°C) fluids that are injected into the ocean from these vents are rich in dissolved metals. One of the more enriched metals is iron (Fe), which an essential micro- nutrient for marine plant life that is present in limiting quantities in some areas of the global ocean. However, it is reactive in seawater, and therefore a non-reactive element is required in order to quantify its transport in seawater. Here we discuss the use of radium isotopes to trace the pathway of hydrothermal iron in the Pacific and Atlantic Oceans [1].

2 Results and Discussion

Radium isotopes are enriched in hydrothermal fluids and 228 226 long-lived Ra (t1/2 = 5.75 y) and Ra (t1/2 = 1600 y) have been used to measure hydrothermal processes, including the residence time of fluids in the crust and the age of basalt chimneys. However, fewer studies have 223 employed the shorter- lived Ra (t1/2 = 11.4 d) and 224 Ra (t1/2 = 3.66 d), or used Ra to study the dynamics of 228 neutrally-buoyant hydrothermal plumes. In a young Fig.1. Activities of Ra measured at the HADES facility hydrothermal plume (days-months), short-lived Ra compared to activities on separate samples measured in an isotopes can be modeled to determine the time elapsed underground lab in Modane, France. The measured activities between venting and sampling. For older plumes (years- from the two facilities agree well and are elevated between 228 2400 – 2550 m due to influence from a hydrothermal plume. decades), Ra (t1/2 = 5.75 y) can be used in a similar manner. In both applications, the Ra isotope is normalized to either a longer-lived Ra isotope (e.g. References 226Ra) or a conservative tracer (e.g. 3He) in order to correct for the effects of dilution such that any decrease 1. Kipp, L.E., V.S. Sanial, P.B. Henderson, P. van in Ra activity is primarily due to decay. Most Beek, J-L. Reyss, D.E. Hammond, W.S. Moore, and importantly, these Ra ages can be applied to determine M.A. Charette. (2017) Radium isotopes as tracers of the transport rates and residence times of trace metals in hydrothermal inputs and neutrally buoyant plume the plume. dynamics in the deep ocean. Marine Chemistry, in press. Seawater samples for radium isotope analysis were collected during cruises to the Mid-Atlantic Ridge (MAR) and the East Pacific Rise (EPR) during 2011 and 2013, respectively. Due to the low activities of 228Ra in seawater, we cannot use conventional above-ground gamma spectroscopy for its determination. In collaboration with the HADES underground counting

* Corresponding author: [email protected] 23

Adsorption of caesium on different types of activated carbon

S. R. H. Vanderheyden1, R. Van Ammel2, K. Sobiech-Matura2, K. Vanreppelen1,3, S. Schreurs3, W. Schroeyers3, J. Yperman1, R. Carleer1

1 Research Group of Analytical and Applied Chemistry, CMK, Hasselt University, Diepenbeek, Belgium

2European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel, Belgium

3Research Group of Nuclear Technology, CMK, Hasselt University, Diepenbeek, Belgium

1 Introduction the samples in a NaI well detector (nearly 100% efficiency for Cs-134) and in an ionisation chamber. Cs- Cs-137 (T1/2 ≈ 30 years) is an important long-term 134 serves as a tracer for the total amount of Cs in the contributor to environmental contamination. It is solution and its activity can be correlated to the released into the biosphere by nuclear weapons testing or concentration. reactor accidents [1]. For example, the release by the Adsorption experiments are carried out at 3 different accident at the Fukushima Daiichi nuclear power plant pH's using 10 different ACs: 2 commercially available raised the Cs-137 concentrations in the local AC's (Norit G1240, Filtrasorb F400), 3 AC's from BSG, groundwater to concentrations above the drinking water and the same 5 AC’s previously loaded with a small limit in downstream areas like the Fukushima port [2]. amount (0.5 %) of Prussian Blue (PB) prior to the Cs salts are very soluble in water, but strongly bind to adsorption experiment in order to further enhance Cs soils and minerals (Public Health Service, 2004). These adsorption. The amount of PB on the AC’s is determined properties are used to investigate the removal of Cs from by calculating the difference between the iron water using a wide range of low-cost adsorbents [3]. concentrations (measured via ICP-AES) of a PB solution In order to remove (radio-)caesium from water, before and after adsorption of PB on AC. Approximately adsorption on activated carbon (AC) is suggested as an 25-30 mg of AC is put into contact with 9 g of the active economical and straightforward method to concentrate Cs solution (±1.2 ppm Cs; 0.6 Bq/g) and the total low levels of Cs on a compact adsorbent. Considering activity is determined by measuring the tubes in the NaI the high pH point of zero charge of several ACs, well. These tubes are shaken for 36 hours. The solution adsorption should be performed at high pH [4]. The goal is filtered using plastic funnels and Whatman ashless of this work is to determine the best adsorption filters to separate the AC from the solution. The emptied conditions for removal of low levels of Cs from tubes, the filters with AC and the tubes with the radioactive wastewater, using AC. In this research, ACs collected solutions are measured in the NaI well. From from brewer’s spent grain (BSG) are compared to two the measurement, the fraction of Cs-134 adsorbed on the commercially available industrial ACs. The BSG AC’s AC and the fraction remaining in the solution are are produced in a tube reactor using steam activation [5]. calculated. For the column experiments, Bio-rad Poly- Prep Chromatography Columns (0.8 x 4 cm) (Bio-Rad, California, USA) were filled with approximately 0.7 g of 2 Experimental Norit GAC 1240 and pre-wetted with water. 11 mL of approximately 37 Bq g-1 134Cs solution at pH 4, 7, 10 and 2.1. Methods and materials 12 was poured over these columns and collected, by gravity, in a centrifuge tube. The activity of the collected A 1000 ppm Cs (σ= 29 barn) standard solution (VWR solution, as well as the activity remaining in the empty CertiPur, traceable to NIST) was irradiated in the centrifuge tube, were both measured in the well-type neutron flux of the BR-1 reactor at SCK-CEN Mol to detector. The collected solution was then poured over the obtain a Cs-134 solution. From the mother solution, column again. This cycle was repeated five times. three dilutions with different pH (7, 10 and 12) were prepared, adjusting the pH with ammonia. Dilution factors and concentrations were calculated by measuring

* Corresponding author: [email protected] 24

2.2 Results References

Properties of the adsorption behaviour of Cs are 1. Whicker, F.W., et al., Cesium-137 in the displayed in Table 1. Both the activity concentration and Environment: Radioecology and Approaches to Cs concentration are displayed before and after Assessment and Management, in NCRP Book adsorption from a solution with different pH, averaged No. 154 National Council on Radiation for the three ACs. The removal percentage is also Protection and Measurements. 2007, Bethesda. calculated. Adsorption is limited at each pH, but the 2. TEPCO, Detailed analysis results in the port, highest removal percentage is reached at a pH of 10. discharge channel and bank protection at Higher pH leads to competition with ammonia. Fukushima Daiichi NPS (As of August 28). pH Activity Cs Activity Cs Removal 2013. concentratio concentrati concentrati concentratio percentag n before on before on after n after e 3. Li, D., et al., Aqueous 99Tc, 129I and 137Cs adsorption adsorption adsorption adsorption removal from contaminated groundwater and (Bq g-1) (mg L-1) (Bq g-1) (mg L-1) 7 59.2 ± 0.7 1.16 ± 0.01 48.6 ± 1.9 0.95 ± 0.04 18 ± 3 sediments using highly effective low-cost 10 59.7 ±0.7 1.17 ± 0.01 47.1 ± 1.3 0.93 ± 0.02 21 ± 2 sorbents. Journal of Environmental 12 60.4 ± 0.7 1.19 ± 0.01 49.2 ± 1.2 0.96 ± 0.02 19 ± 1 Radioactivity, 2014. 136(0): p. 56-63. 4. Hanafi, A., Adsorption of cesium, thallium, Table 1: Average Cs concentration in adsorption solutions strontium and cobalt radionuclides using and on AC surface of experiments at 3 pHs. activated carbon Journal of Atomic and Fig. 1 displays the influence of pH on the adsorption Molecular Sciences, 2010. 1(4): p. 292-300. capacity for Norit GAC1240 after a number of filtration 5. Vanreppelen, K., et al., Activated carbon from cycles using 1 column. The competition effect with pyrolysis of brewer’s spent grain: Production ammonia limits the adsorption capacity at high pH, and adsorption properties. Waste Management washing away the Cs from the AC. At neutral or slightly & Research, 2014. acidic pH, the adsorption capacity reached its maximum after approximately 3 to 4 cycles.

Influence of pH on column adsorption 0.01 0.008 pH 4 0.006 pH 7 0.004 pH 10

q (mg Cs/g AC) Cs/g (mg q 0.002 0 pH 12 0 1 2 3 4 5 Number of cycles Fig.1. Influence of solution pH on the adsorption capacity of a Norit GAC1240 column after several uses.

3 Conclusions

Batch experiments using a variety of ACs adsorbing Cs from solutions with different pH showed no significant difference between the adsorption capacities at equilibrium for Cs (expressed as qe values in mg Cs per gram AC) on either commercial AC or AC from BSG. Also the difference in adsorption between the Cs solutions of different pH was not significant. Binding PB on the ACs prior to the adsorption of Cs showed no significant effect on the qe for any of ACs. A column experiment with Norit GAC 1240 using 4 solutions with a different pH showed that a neutral to slightly acidic pH increased the adsorption of Cs. At a higher pH the effect of the competition with ammonia ions caused a decrease of qe.

25

Uptake of radionuclides in plants: a case study on rice (Oryza sativa) exposed to radiocaesium.

Nele Horemans1,*, Shinichiro Uematsu1, May van Hees1, Hildegarde Vandenhove 1, Lieve Sweeck1 1 Biosphere Impact Studies, SCK•CEN, Belgian Nuclear Research Centre, Boeretang 200, B-2400 Mol, Belgium

1 Introduction and hypothesis radiocaesium uptake but also increased radiocaesium uptake by the stem base. Rice is economically of major importance as food crop. Further we were able to demonstrate that reducing the K In Japan after the nuclear accident of 2011 in Fukushima supply to the roots significantly increased the uptake many vast areas of agricultural land got contaminated by through the stem base as well as its accumulation in the different radionuclides in particular cesium. The transfer shoots. On the other hand the translocation from the stem of radiocaesium (Cs-137 and Cs-134) from the soil to base to the shoots was less affected by the K supply crops like rice is of considerable interest as through this compared to that from roots to shoots. This study was food chain humans are possible exposed to enhanced the first to experimentally demonstrate active and levels of radiation. Rice (Oryza sativa) in the affected internally regulated radiocaesium uptake by the stem area is widely cultivated in flooded conditions in paddy base of rice. fields, where the base of the above-ground shoot of the The uptake of radiocaesium via the stem base can have plants is intermittently submerged in flooded water, environmental significance as scenario calculations for whereas roots grow in radiocaesium-contaminated soils. the Fukushima-affected area predict that radiocaesium in The flooded water contains radiocaesium since the irrigation water could be an important source. However irrigation water is derived from rivers or ponds fed by the equal radiocaesium activity concentrations in the runoff and drainage in the Fukushima-affected area [1] It external solutions in the stem base and root was still unclear what fraction of radiocaesium can be compartments are unlikely to occur in the field, where taken up via the stem base of rice plants from the RCs concentration in irrigation water is typically lower irrigation water. The prevailing idea is that the major than that in soil solutions. To further study this it will be part of radiocaesium in rice plants is derived from soils necessary to perform field tests as well as monitor the via root uptake. concentrations of radiocaesium in both irrigation water and soil solution. Also it might be better to cultivate rice under intermittent irrigation rather than in continuous 2 Results and discussion paddy conditions to reduce the contact period of the stem This work and started with the development of a bi- base to flooded water. This work was part of the PhD of compartmental device which discriminates the stem base S. Uematsu and was recently published in The New from root radiocaesium uptake from solutions, thereby Phytologist [2]. using the two different cesium isotopes (Cs-137 and Cs- 134) with < 2% solution leak between the compartments. References The measurement of the cesium isotopes was partly funded by the European Commission’s Joint Research 1. Yoshikawa N, Obara H, Ogasa M, Miyazu S, Centre within HORIZON2020 via the EURATOM Harada N, Nonaka M. 137Cs in irrigation water and access work package, EUFRAT. its effect on paddy fields in Japan after the We could demonstrate that radiocaesium uptake was Fukushima nuclear accident. Science of the Total linear over time (0–24 h) and that its uptake to the entire Environment 481, 252-9. (2014) plant, expressed per dry weight of the exposed parts, was 2. Uematsu S, Vandenhove H, Sweeck L, Hees MV, sixfold higher for the roots than for the exposed stem Wannijn J, Smolders E. Foliar uptake of base. At equal radiocaesium concentrations in both radiocaesium from irrigation water by paddy rice compartments, the exposed stem base and root uptake (Oryza sativa): an overlooked pathway in contributed almost equally to the total shoot contaminated environments. New Phytol 214, 820- radiocaesium concentrations. Reducing potassium 9. (2017) supply to the roots not only increased the root

* Corresponding author: [email protected] 26

Nuclear data for applications from JRC Geel and HZDR

Arnd Junghans,*,

1 Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany

Nuclear reactions induced by fast neutrons are of high target sample relative to the count rate without sample relevance in several fields of nuclear applications: and is independent of the neutron detection efficiency. Transmission measurement at GELINA [5,6]starting in Neutron-induced fission of transuranium isotopes is of the resolved resonance region up to about 100 keV have relevance for the development of transmutation 242 been complemented by experiments at nELBE [7] in the technology for spent nuclear fuel. The nuclide Pu is fast neutron region allowing to extend the energy range the longest-lived plutonium isotope produced in thermal of the data up to the series of measurement from spectra in nuclear power reactors and it’s fission cross LANL[8] at energy extending from 5 to 560 MeV. section needs to be known with a high accuracy (~ 5 % The nELBE photoneutron source has favourable uncertainty) for the assessment of integral reactor 242 conditions for transmission measurements due the low parameters [1]. The Pu(n,f) cross section was recently instantaneous flux of neutrons and low gamma-flash measured at NPL and JRC Geel using background. quasimonoenergetic neutrons [2] and also at HZDR [3] Several materials of interest (in part included in the using the photoneutron source nELBE. CIELO evaluation or on the HPRL of OECD/NEA) have been investigated: 197Au, natFe, natW, 238U, natPt, The inelastic scattering of fast neutrons is an important 4He,natNe,natXe. process in the slowing down of neutrons in many In my talk I will present results on the experiments materials as the kinetic energy loss is usually much mentioned above from the different neutron facilities at larger than the loss through the recoiling nuclei in elastic Geel and HZDR in order to show how the different scattering. In measurements of the inelastic cross section neutron source complement each other. the neutron fluence is usually determined using neutron- The author wishes to express his sincere gratitude to induced fission standards e.g. using parallel plate fission Franz-Josef Hambsch, Wim Mondelaers, Arjan ionization chamber. At GELINA recently a new 7 Plompen, Peter Schillebeeckx and all colleagues at JRC measurement of the Li(n,n’) gamma-ray production Geel for many years of fruitful collaboration in the cross section was made using the GAINS setup.[4] and a European research framework. higher value of the cross section than previously was 7 This work is supported by the EURATOM FP7 project found. Li(n,n’) has several properties that allow it to CHANDA and by the German Federal Ministry of become a future standard cross section for inelastic Education and Research (03NUK13A). scattering, e.g. isotropic gamma-ray emission of only a single gamma-ray of 478 keV from threshold (546 keV) References to about 5 MeV, where breakup starts to set in. Neutron 1. OECD/NEA High Priority Request list entry 39H scattering on lithium is also relevant for fusion research https://www.oecd-nea.org/dbdata/hprl/hprl.pl as the tritium breeding requires a lithium containing 2. P. Salvador-Castiñeira et al., Phys. Rev. C 92 (2015) blanket. 7 044606 In order to help establish Li(n,n’) as a standard reaction 3. T. Kögler et al., EPJ Web of Conf. 146 (2017) an experiment using the same LiF targets was conducted 11023; T. Kögler PhD thesis, TU Dresden (2017) at the photoneutron source nELBE of HZDR. 4. M. Nyman et al., Phys. Rev. C 93 (2016) 024610 5. I.Sirakov et al., Eur. Phys. Jour. A49 (2013) 49 Neutron total cross sections are an important source of 6. I. Sirakov, et al., Eur. Phys. Jour A 53 (2017) 199 experimental data in the evaluation of neutron-induced 7. R. Hannaske et al., Eur. Phys. Jour A 49 (2013) 137 cross sections. They can be measured in a transmission 8. W.P. Abfalterer et al., Phys. Rev. C 63 (2001) experiment, which allows for a precision in the few 044608 percent range. The transmission determined from the count rates of the neutron beam transmitted through the

* Corresponding author: [email protected] 27

Neutron inelastic scattering studies with GRAPhEME at GELINA

M. Kerveno1,*, C. Borcea2, Ph. Dessagne1, M. Dupuis3, G. Henning1, S. Hilaire3, A. Negret2, M.

Nyman4, E. Party1, A. Plompen4

1Université de Strasbourg, CNRS, IPHC UMR 7178, Strasbourg, France

2Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania

3CEA, DAM, DIF, Arpajon, France

4European Commission, Joint Research Centre, Geel, Belgium

1 Introduction its measurement capabilities to very active actinide samples (see Fig.1.) A first measurement campaign with a 233U target is currently running. The next step is To address the specific challenges related to the foreseen with a 239Pu sample which supposes that the reduction of (n,xn) and neutron inelastic scattering sample preparation challenge would be solved by the uncertainties, our collaboration has developed, at the target laboratory of EC-JRC-Geel. Obviously, this work EC-JRC-Geel GELINA facility, an experimental device program is supported by the open access programme based on the prompt gamma spectroscopy method EUFRAT. coupled to neutron time of flight measurements. Indeed, neutron inelastic scatterings, in the context of nuclear reactor researches, are important processes (slowing down) as the cross sections impact the neutron energy distribution in the reactor core and thus modify core parameters like radial power or keff as it has been demonstrated in several works [1, 2, 3].

2 GRAPhEME at GELINA Among the three available experimental methods, direct neutron detection, activation and prompt gamma-ray Fig. 1.The upgraded GRAPhEME setup with the segmented spectroscopy, our CNRS-IPHC, EC-JRC-Geel and IFIN- Germanium detector at the GELINA FP16-30m. HH collaboration has chosen the last one to get rid of To address the uncertainty challenges related to inelastic neutron detection difficulties and restricted experimental scattering (e.g. uncertainty target about a few percent for application of the activation technique. We have thus 238U), GRAPhEME has been accurately characterized to developed the GRAPhEME setup (GeRmanium array for γ Actinides PrEcise MEasurements) at the GELINA produce as accurate as possible (n,xn ) cross sections. facility, the multiuser neutron time-of-flight facility Collaboration work with theoreticians is also underway γ operated by EC-JRC-IRMM, in Geel, Belgium. Since to use the measured (n,xn ) cross sections combined 2005, the GRAPhEME setup has been especially with modelling results for the (n,xn) cross sections designed to study actinides at the flight path 16 - 30 m. determination [5]. In a first phase, measurement campaigns have been performed on low active actinides (235,238U, 232Th) and tungsten isotopes (182,183,184,186 and natural) [4]. At least in 2015, GRAPhEME has been upgraded with a segmented (36 pixels) Germanium detector to increase

* Maëlle Kerveno : [email protected] 28

3 Outlook of the presentation

The presentation will start with a brief history of the GRAPhEME setup up to now, emphasizing the main steps. The second part will focus on the work performed during EUFRAT with the very active targets. Finally, the last part will be dedicated to the review of the experimental method limitations and the different projects foreseen in the coming years to produce accurate (n,xn) cross sections from (n,xn γ) cross section measurements.

References

1. A. Santamarina et al., Nuclear Data Sheets 118 (2014) 118–121 2. M. Salvatores and R. Jacqmin, Nuclear Science- NEA/WPEC-26, Volume 26, NEA N° 6410 (2008). 3. P. Romojaro et al., Ann. Nucl. Energy 101, 330-338, 2017 4. M. Kerveno et al., Eur. Phys. J. A (2015) 51: 167 5. M. Kerveno et al., Eur. Phys. J Web of Conferences 146, 11012 (2017)

29

Time-of-flight measurements on natural Ag and MINERVE Ag samples at GELINA facility

L. Šalamon1,*, B. Geslot1, J. Heyse2, S. Kopecky2, P. Leconte2, G. Noguere1, C. Paradela2, P. Schillebeeckxt2, L. Snoj3

1 DER, DEN, CEA, Cadarache, F-13108 Saint-Paul-lez-Durance, France

2 EC-JRC-Geel, B-2440 Geel, Belgium

3 Reactor Physics Division, Jozef Stefan Institute, SI-1000 Ljubljana, Slovenia

1 Introduction FP5, respectively) was performed with standard thick and thin natural silver samples (thickness: 0.25, 0.126, A wide number of isotopically enriched samples 0.06 mm) available at EC-JRC Geel in order to improve (containing fission products and actinides) were the existing resonance parameters of silver isotopes measured in the MINERVE reactor in frame of the Burn- Ag107 and Ag109 in the resolved resonance range (up to Up Credit, MAESTRO and OSMOSE program with a 1 keV). Black resonance technique was used for the pile-oscillation technique. Among the isotopes measured background estimation (by using black resonance filters in MINERVE, Rh103, Tc99, Am241 and Np237 were in the neutron beam). Before background subtraction all also measured at GELINA facility with the TOF the spectra obtained were corrected for the dead time of technique through transmission and capture the detection system and normalized to the same neutron measurements (data included in JEFF evaluation). A intensity. Final spectra were in the form of transmission good agreement between integral and microscopic data and capture spectra. In next phase transmission is obtained for Rh103 and Np237, while discrepancies measurements were performed at FP13 with the remain unexplained for isotopes Tc99 and Am241. MINERVE samples. First two samples are made of UO2 Difference between MINERVE and GELINA data can matrix and doped with different enrichment of Ag109 be investigated by using the MINERVE samples for (AG9C1 and AG9C2), third one is made of Al2O3 transmission measurements at GELINA. This allows matrix doped with natural silver (AAG) and the last one separation of the contribution from the thermal neutrons is the natural silver dissolved in HNO3 (MAG). Samples and contribution due to the resonance region. The main are enclosed in Zircaloy-4 containers (plus aluminum difficulty of such experiment is linked to the container in case of MAG sample). All samples were characteristics of the MINERVE samples. The samples positioned upright with the axis of cylinder in z routinely used for oscillation measurements are direction, perpendicularly to the neutron beam. Size of cylindrical samples of 10 cm length and with a diameter the beam has been carefully adjusted in a way to have of 1 cm. For TOF measurements in GELINA facility larger diameter than the sample diameter, but small optically thin discs with diameters 2-8 cm are used. enough to keep the dead-time correction valid for These samples are optimized to perform transmission increased count rate due to the “void” (part of the measurements in a good transmission geometry, while neutrons not passing through the sample). Data reduction MINERVE samples are not optimized for such follows the same steps as we did for transmission spectra experiments. Experimental feasibility study with silver of the standard samples, but in addition it also includes MINERVE samples was performed to investigate the the implementation of “alpha” parameter. Transmission capability of extracting reliable results (i.e. resonance involving alpha parameter is corrected for the void (in parameters) from data obtained with MINERVE type of spectra seen as increased level of transmission dips), samples. which brings the levels of saturated resonances to transmission equals to zero. 2 Time-of-flight measurements

In first part of experimental campaign a combination of transmission and capture measurements (at FP13 and

* Lino Šalamon: [email protected] 30

3 REFIT resonance shape analysis the range of uncertainties (discrepancies of composition up to 2%). Experimental data (transmission and capture data from standard samples) was simultaneously analyzed by AAG sample contains no U238, but has almost identical resonance shape analysis code REFIT, which is based on geometrical properties as enriched MINERVE samples. the Reich-Moore approximation of the R-matrix Therefore the same effective diameters can be used for the composition verification. A good agreement for formalism. New resonance parameters (, and ) of Ag107 and Ag109 have been extracted for the resonance Ag107 and Ag109 isotopic composition is obtained from the ratios (< 2% difference). region up to 1 keV (average has been used in energy region 100-1000 eV). 4 Conclusions Resonance analysis of transmission measurements with MINERVE samples required modification of New resonance parameters of silver isotopes 107 and transmission expression in REFIT in order to account for 109 were extracted from the simultaneous analysis of the thickness distribution in radial direction. The validity transmission and capture data of natural silver. New of analytical expression has been demonstrated with the model that describes the shape of MINERVE samples Monte Carlo simulations. First, analysis with the was successfully implemented in the REFIT code and MINERVE samples enriched in Ag109 (AG9C1, tested with Monte Carlo simulations and transmission AG9C2) has been performed. Resulting spectra contain data resulting from measurements with four different many U238 resonances, for which we believe to have MINERVE samples. Isotopic composition of samples good knowledge of the resonance parameters in the was verified by REFIT shape analysis of U238, Ag107 resonance range (we used U238 JEFF-3.3t evaluation, and Ag109 resonances, and good agreement with the based on measurements at GELINA facility). The best measured values was obtained. This feasibility study has values of the effective sample and beam diameter (used shown the importance of neutron beam collimation to as parameters in the transmission model) and the obtain reliable results. Conditions close to a parallel parameters of the analytically described resolution beam between sample and detector, and “flat” radial function have been determined from the minimum chi- profile of the beam are proposed for the future square value resulting from the comparison of experiments of the same type. experimental data (in the regions of U238 resonances) with the REFIT calculation. Effective sample and beam diameter are related through the geometrical analytical expression involving alpha parameter, which is obtained from the experimental data. As the diameter values could be compensated by the resolution function, only low energy resonances (below 100 eV) were considered. Effective sample diameter that describes the best the shape of U238 resonances was shown to be smaller than the physical diameter of the sample (without considering the cladding). This may be attributed to collimation of the flight path as neutron beam intensity is radially distributed. What is more, collimation between the sample and the detector affects the ratio between the void and the sample area, which is believed to be not exactly the same at sample and detector position.

Isotopic composition of enriched silver samples (U238 and Ag109 isotopes) was verified by the shape analysis with the REFIT code. Area of the transmission dip is proportional to the atomic density and the of the resonance, therefore the ratio of the original and fitted value, that describes the best the shape of the resonance, gives us information about the composition. The ratios of U238, using JEFF3.3t evaluation, were calculated for several resonances in the energy region of interest (up to 1 keV) and a good agreement, with the average discrepancies per data set below 2%, was obtained. The same exercise was repeated for the Ag109 isotope, where new evaluation of silver resonances, produced in this work, was used. The ratios of were in good agreement with the given composition of silver in 31

Integral Experiments in the GELINA Target Hall on 238U

P Leconte1,*, B. Geslot1, P. Archier1, 2 2 2 2 2 2 2 A. Plompen , M. Nyman , C. Diaz Vizoso , G. Pettinicchi , H. Spruyt , R. Wynants , P. Siegler

1 CEA, DEN, DER/SPRC/LEPh Cadarache, F-13108 Saint Paul-Lez-Durance, France.

2 EC-JRC, SN3S, B-2440 Geel, Belgium

1 Introduction spectrum. A photograph of the target are displayed in Figure 1. In shielding experiments the attenuation of a neutron flux passing through a material is measured. These kinds of experiments are of interest for radiation protection, and also for nuclear data evaluators as a way to validate neutron inelastic scattering cross sections. SINBAD [1] is an international collaboration to store, evaluate and share shielding experiments that were made by different countries. A large part of these experiments are quite old and not all of them have the sufficient quality assurance to be used for nuclear data evaluation. Moreover, heavier materials than tungsten are not included. 238U for instance belongs to a high priority request list at OECD/NEA [2] due to its importance on both thermal Fig.1. Photograph of the GELINA neutron-production target and fast reactor studies. For this reason performing new shielding experiments, with a level of uncertainty of less A general view of the target hall is shown in Figure 2. σ than 5% at 1 , is important. Such an experiment, called The shadow bars used to block the direct neutron flux EXCALIBUR, was recently performed at the CALIBAN from the target and thus allowing only the moderated facility at Valduc [3], but showed that a repeat of the neutron spectrum to be used in certain flight paths are measurement should be made. Since CALIBAN was clearly visible on a table to the right of the target closed down this repeat needs to be at a different facility. position. The effect of shadow bars and collimator on the present experiment needs to be investigated. The table is This paper is describing the first attempt to use the equipped with a tray mounted on ball bearings, so it can pulsed white neutron source GELINA at JRC Geel to be moved over the full length of the table. This allowed perform shielding experiments within the target hall, the removal of dosimeters after the irradiations to be using Uranium disks and activation foils to measure the done in a more benign radiation environment. spectrum averaged transmission rate.

2 The GELINA neutron source and the target hall

The GELINA neutron-production target is a torus of depleted uranium, containing 10% molybdenum by weight. A pulsed electron beam from the GELINA accelerator hits the target, typically at 800-Hz frequency. Neutrons are produced by bremsstrahlung-induced (γ,xn) and (γ,f) reactions. Cooling of the target is achieved by flow of mercury through the target support structure, and by helium flow around the torus. A water moderator in beryllium casing is used to produce a slow neutron spectrum. For the present experiments the moderators Fig.2. General view of the target hall. The shadow bars are were placed as far from the target as possible at about 50 clearly visible on the table in front of the red shutters. cm. With the moderator, the majority of the neutron flux falls between 10 meV and 20 MeV. Without moderator The first integral transmission experiment performed at the spectrum starts from about 1 keV. The maximum GELINA used several disks of depleted uranium which neutron emission rate in GELINA is 3.2 × 1013 s-1, which were available at JRC Geel. The uranium disks were corresponds to a 300-W irradiation in CALIBAN (the encapsulated in aluminium casing and placed close to the maximum is 1 kW). The neutron spectrum from neutron source. Neutron activation foils (dosimeters) GELINA is fission-like, similar to the fission neutron were located between the plates in aluminium holders to make relative activation measurements with respect to a reference dosimeter at the front.

* Corresponding author: [email protected] 32

3 Description of the experiment The dosimeters that were used are aluminium, uranium, cobalt, iron, indium, magnesium, nickel, rhodium, The experiment was performed at JRC Geel from 19th to titanium, and gold. They have a diameter of 40mm 23rd of September 2016. Thirteen disks of depleted (except uranium foils which are 12mm) but vary in uranium were used in the experiment, giving a total thickness from 10 to 500µm. They have been weighed Uranium thickness of 150 mm (see Figure 3). The disks on a balance with an accuracy of ±1mg (1σ). The were packed into six aluminium containers, each one thickness was evaluated based on mass and area containing about 30mm of uranium with the addition of measurements. The list of radionuclides that were 0.5 mm aluminium on each side. γ-spectrometry measured in the activated foils is given in Table 1. measurements were performed on one of them in order to record the 186 keV and 1001 keV peaks Table 1. Reactions used in the experiment corresponding respectively to 235U and 238U decay. The 235 U mass enrichment of the disk was found to be Dosimeter Reactions t1/2 (0.264±0.012)% (1σ). Rh 103Rh(n,n’γ)103mRh 0.9 h Mg 24Mg(n,p)24Na 15 h Fe 56Fe(n,p)56Mn, 2.6 h, 312 d 54Fe(n,p)54Mn In 113In(n,γ)114mIn, 50 d, 4.5 h 115In(n,n’γ)115mIn Ti 48Ti(n,p)48Sc, 44 h, 3.4 d, 84 d 47Ti(n,p)47Sc, 46Ti(n,p)46Sc Au 197Au(n, γ)198Au, 2.6 d, 6.1 d 197Au(n,2n)196Au In 113In(n, γ)114mIn, 50 d, 4.5 h

115In(n,n’γ)115mIn Fig.3. Depleted Uranium disk Rh 103Rh(n,n’γ)103mRh 0.9 h

The encapsulated uranium disks were placed 76 cm from Ni 58Ni(n,p)58(g+m)Co 71 d the target for the irradiations. A schematic of the Co 59Co(n,p)59Fe, 45 d, 2.6 h experimental arrangement is shown in Figure 4. 59Co(n, γ)56Mn Al 27Al(n, γ)24Na 15 h Ni 58Ni(n,p)58(g+m)Co 71 d U 238U(n,f)PF -

Two coaxial HPGe detectors, equipped with Pb-shields, were used for the post-irradiation measurements. One was located in the GELINA flight-path area (flight path Fig.4. Schematic of the experimental arrangement for Uranium 2 / 50 m), and another in building 020. The first is a Canberra BEGe detector (crystal diameter 81 mm, Activation foils were packed into aluminium holders, thickness 31.5 mm), the second an ORTEC coaxial consisting of two aluminium plates placed against each detector (crystal diameter 81.7 mm, thickness 88.8 mm). other, forming a 1-mm thick central cavity between The Canberra detector was equipped with a 0.6-mm them. The holders were placed between the uranium thick carbon-epoxy window, facilitating the detection of γ containers, as presented in Fig.5 low-energy rays. The dosimeters were positioned on plastic support cylinders to put them at various distances (contact, 5 cm, and 10 cm) from the detector window. This was done to adjust the counting rates to minimize dead-time effects. A picture of typical dosimeter measurement geometry is shown in Figure 6. Some dosimeters with very low activities (Ti, Fe, Co, and Ni) were sent after the experiment to LPSC/CNRS in Grenoble for longer measurements.

The analysis of the raw data consists in computing the Integral Transmission Rate (ITR), noted T(x), which is defined as follows: Fig.5. Support for the Uranium slab 33

T(x) = R(x) / R(0) (1) experimental device, especially the concrete walls, has to be accounted for, due to a non-negligible contribution of where R(x) defines the microscopic activation rate on the back-scattered neutrons [4]. This effect may be dosimeter placed behind a thickness of Uranium ∆x and responsible for a few tens of percents deviation from the R(0) is the microscopic activation rate on the dosimeter calculation without walls, especially for low energy placed on the front size of the Uranium slab. threshold reactions like Rh(n,n’γ), but it becomes negligible for high energy threshold reactions (E50% > 8 MeV).

The interpretation will consider also the validation of the neutron flux spectrum and its impact on the analysis of integral transmission rate measurements. Time-of-flight data that were acquired in the FP-30m will be used for this purpose.

5 Conclusions The current Uranium experiment is the first of a kind. Using the pulsed neutron source GELINA, it was shown that shielding-type experiments were feasible in the target hall of the facility. These integral benchmarks are relevant to validate scattering cross sections, as a Fig.5. A typical dosimeter measurement geometry. complement to time-of-flight experiments.

We present in Figure 6 the ITR for the different Based on the feedback of this first experiment where the threshold reactions. preliminary analysis has shown that the room return effect was responsible of a distortion of the neutron flux, a proposal for a new experimental configuration was submitted to EUFRAT. The intention is to prepare an optimized set-up with a shielding of 15 cm thick polyethylene plus 5 mm thick boron carbide, preventing the interaction of back-scattered neutrons on the dosimeters.

Other applications than Uranium are under consideration for the next years, based on materials of interest for 4th generation-type reactors, like ASTRID, or experimental facilities like MYRRHA, including iron, magnesium oxide, sodium, tungsten, lead and bismuth.

Fig.6. Integral Transmission Rate References for the different activation reactions 1. I. Kodeli, A. Milocco, Pedro Ortego and Enrico Sartori, 20 Years of SINBAD (Shielding Integral 4 Monte-Carlo model of the experiment Benchmark Archive and Database), Progress in Nuclear Science and Technology, Volume 4 (2014) The interpretation is currently ongoing. It consists first in pp. 308-311. a precise modelling of the GELINA target hall, using 2. NEA Nuclear Data High Priority Request List, CAD models provided by JRC and conversion software https://www.oecd-nea.org/dbdata/hprl/ to generate an input file for the CEA Monte-Carlo code 3. D. Bernard, P. Leconte et al., EXCALIBUR at TRIPOLI4. An MCNP5 input file will be produced in CALIBAN: a neutron transmission experiment for the same way. 238U(n,n’) nuclear data validation, Proceedings of

the International Conference ANIMMA 2015, Then, we are investigating the adequate calculation route Lisboa (Portugal), April 2015. to compute the ITR. Indeed, due to the very high 4. P. Leconte, C. De Saint Jean, B. Geslot, A. computation time required to simulate the complete Plompen, F. Belloni, M. Nyman, On the feasibility process of electron irradiation, followed by photon to perform integral transmission experiments in the generation by Bremsstrahlung, then by photonuclear GELINA target hall at IRMM, Proceedings of the reactions, before propagating the neutrons through the ICRS13 conference, Paris, 2016. target hall, a one-step calculation very slowly converges. Design studies have shown that the environment of the 34

Accurate measurement of the 92Zr and 89Y neutron capture and transmission cross section

G. Tagliente1,*, L. Damone1, J. Heyse2, S. Kopecki2, A.C. Larsen3, M. Mastromarco1 C. Paradela2 and P. Schillebeeckx2

1 Istitituto Nazionale di Fisica Nucleare, sez. Bari, I-70126 Italy

2 European Commission, Joint Research Centre, B-2440, Geel Belgium

3 Department of Physics, University of Oslo, N-0316, Norway

1 Introduction the next bottleneck at nuclei with a neutron magic number of 82, i.e. Ba, La, Ce (defining the "hs" s-process The neutron cross sections for Zr and Y isotopes are index). This means that the neutron-capture cross section important for several aspects in traditional and advanced of Zr and Y not only influence the abundance of Zr and nuclear technologies and nuclear astrophysics. Y produced by the s-process, but also the whole Zirconium is considered the best suitable metal among abundance distribution. The abundance of Y in stars is the cladding materials for the production of nuclear fuel relatively easy to derive from high-resolution light element for all reactor types. In particular zirconium spectra. Each element in the atmosphere of the star has a alloy materials are the skeletons of the fuels assemblies specific “signature” a specific set of line, in particular and are used to make the sealed tubes enclosing the fuel the Y has many strong lines, this ensures that some of pellets. The small neutron capture cross sections, in them are always available, depending on the spectra combination with favorable chemical and mechanical coverage (hence its inclusion in all studies to determine properties are the main advantages for such kind of "ls"). As a consequence, Y has been used extensively to employments. constrain stellar models [3] and even astrophysical Yttrium hydride offers advantages as a moderator for scenarios, e.g., related to the origin of chemical high temperature thermal nuclear reactors. In contrast to anomalies in ancient globular clusters [4]. Furthermore, other hydrides considered as moderators, this material it is currently hotly debated if AGB stars can account for retains its relatively high content of hydrogen at elevated the total abundance of Y and Zr in the solar system [4-6]. temperatures such as 900 °C to 1200 °C. In addition, the nuclear properties of yttrium hydride are favourable, and its thermal conductivity is excellent [1] 2 Experimental details In astrophysics, the Zr and the Y belong to the first peak of abundances which are attributed to the slow neutron 2.1. Experimental setup capture process (the s process) producing nuclei with mass number 88 ≤ A ≤ 210 in asymptotic giant branch Experiments were carried out at the neutron time-of- (AGB) stars (their production in massive stars is limited flight (TOF) facility GELINA. to a few percent of the total solar abundance [2]). The The capture measurement reported in this work was abundances of Zr, Y and Sr define the "ls" s-process performed at the 60 m measurement station of flight path index routinely used to compare theoretical predictions 14 of GELINA. This flight path form an angle of 9° with with experimental observations. The existence of the respect to the normal of the moderator face viewing the first peak is due to 88Sr, 89Y, and 90Zr having a magic fly path. The transmission measurements were number of neutrons equal 50, therefore, the cross section performed at the 50 m measurement station of flight path for neutron-capture reaction for these nuclei is much 4. For all the measurements the accelerator was lower compared to the cross sections of neighboring operating at 800 Hz and produced an average beam nuclei. Consequently, they act as bottlenecks on the current of about 55 µA. neutron-capture path, controlling the total neutron flux The prompt γ-rays originating from the capture reaction needed to proceed to the production of heavier elements were detected by 4 C6D6 liquid scintillator (NE230) of up to the second s-process peak, which corresponds to 10 cm diameter and 7.5 cm length, each detector was

* Corresponding author: e-mail address 35

positioned at an angle of 125° with the respect to the direction of the neutron beam. 1 For the transmission measurements the neutrons passing through the sample and filters were further collimated 0.8 and detected by a 6.35 thick and 151.6 mm diameter Li- glass scintillator (NE912). 0.6

Counts 0.4 2.2. Samples 2 g Measurements were carried out with enriched metallic 0.2 10 g 17 g samples. Three disks of 92Zr with a diameter of 2 cm and respective thickness of 1, 5 and 8.5 mm were produced 0 1000 10000 100000 at the Oak Redge National Laboratory. The weight of the 89 En (eV) three samples was respectively 2, 10 and 17 g. The Y 92 samples were produce by the Alpha Aldirich, 3 disks of Fig.1. The transmission measurements on the three Zr samples. diameter of 5 cm and thickness of 0.25, 1.28 and 1,91 mm, and mass respectively of 2, 10 and 15 g. The Y samples were encapsulated in a plastic container to prevent reaction with air. In Table 1 are reported the 0.9 characteristics of the samples. 0.8 0.7 Sample Enrichment Atoms/barn Mass (g) 0.6 92Zr 95.2 9.62E-04 2 92Zr 95.2 4.85E-03 10 0.5 92Zr 95.2 8.24E-03 17 0.4 89 Counts Y 99.9 6.90E-04 2 0.3 89Y 99.9 3.45E-03 10 0.2 89Y 99.9 5.17E-03 15 This work Table 1. Characteristics of the samples used in the 0.1 JENDL4.0 measurements 0 44000 45000 46000 47000 48000 49000 50000 En (eV) Fig 2. Comparison of few resonances with library JENDL 4.0. 3 Data analysis Fig. 3 shows the capture measurement on the thinner The AGL and AGS [7] codes developed at the JRC- sample, 2 g, of 92Zr, in this measurement a good GELINA, were used to derive the experimental capture agreement was found with the previous measurement and transmission yields. The AGS code is based on a performed at the n_TOF facility [11] in 2010 expect for compact formalism to propagate all uncertainties starting the resonance in the s-wave, in Fig 4 are shown two from uncorrelated uncertainties due to counting examples of the discrepancy found between the data statistics. reported in [11] and the present data.

0.008 3.1. 92Zr measurements 0.007 0.006 The measurements were performed in 2013 and the data analysis is almost completed. 0.005 In Fig.1 are shown the counts in function of the neutron 0.004

energy in the range from 1 to 200 keV for the three Yield 0.003 samples used in the transmission measurements. In this 0.002 work a substantial difference was found with the previous measurement [8] reported in all the main library 0.001 as JENDL [9] and ENDF[10], in Fig. 2 are showed the 0 comparison with the new data, from this work, and the -0.001 library JENDL 4.0. 10000 En (eV) Fig. 3. The capture measurement on the 92Zr 2 g sample. 36

0.003 0.006 This work 5. S. Cristallo et al., ApJ 801(2015)53 G. Tagliente (2010) 6. S. Bisterzo et al., MNRAS 449(2015)506 0.0025 0.005 7. B. Becker et al., J. of Instrumentation, 7(2012)1002 0.002 0.004 8. J.W. Boldeman et al.,Nucl. Phys. A269(1976)31 9. K. Shibata et al., J. Nucle. Sci. Tech. 48(2011)1 0.0015 0.003 10. M.B. Chadwick et al., Nucl. Data Sheets(2011)2887 Yield Yield 0.001 0.002 11. G. Tagliente et al., Phys. Rev. C81(2010)55801

0.0005 0.001

0 0

-0.0005 -0.001 2400 2500 2600 2700 2800 2900 3000 6200 6400 6600 6800 7000 7200 En (ev) En (ev) Fig. 4. Examples of the discrepancy found between the present measurement and the previous one[11] performed at CERN.

3.2. 89Y measurements The measurement were performed in the summer 2017, the data analysis is currently on progress. In Fig. 5 are shown the preliminary result of the transmission measurements for two different thicknesses of the sample, the counts are shown in function of the neutron energy in a range from 6 to 200 keV.

1.1 1 0.9 0.8 0.7 0.6 Counts 0.5 0.4 89 0.3 Y 10 g 89Y 15 g 0.2 10000 100000 En (eV) Fig. 5 Preliminary results from the 89Y transmission measurements for two different thicknesses of the sample.

4 Conclusions Capture and transmission measurement were performed respectively at 60 m capture measurement station and at the 25 m measurement station in GELINA time-of-flight facility using samples with different characterization. The data of the 92Zr measurements are analysed and they were compared to the previous measurements, The comparison shows sizeable difference in both capture and transmission data.

References 1. Nasa Technical Note NASA TN D-4615 (1968) 2. C. Travaglio et al., ApJ, 601(2004)864 3. V. D'Orazi et al., MNRAS 433(2013)366 4. O. Trippella et al. ApJ 787(2014)414 37

Neutron inelastic scattering measurements performed at the GELINA neutron source

Adina Olacel1,*, Catalin Borcea1, Marian Boromiza1, Philippe Dessagne2, Gregoire Henning2, Maёlle Kerveno2, Alexandru Negret1, Markus Nyman3, Arjan Plompen3

1 Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), Magurele, Romania

2 Université de Strasbourg, CNRS, IPHC, UMR7178, Strasbourg, France

3 European Commission, Joint Research Center, Geel, Belgium

1 Introduction EUFRAT framework and ii) an update of our attempt to measure conversion electrons using DELCO. During the last decade the GELINA (Geel Electron LINear Accelerator) neutron source has been a very 2 (n, n'γ) measurements useful tool in providing nuclear reaction data of interest for many applications, especially for the development of The neutron inelastic scattering experiments performed the new generation of nuclear reactors (Gen IV). up to now using the GELINA neutron source and the Combining the neutron source with the powerful GAINS GAINS spectrometer addressed many different issues. Most of them were related to the High Priority Request spectrometer (Gamma Array for Inelastic Neutron 16 23 28 56 Scattering) and using the time of flight method we were List entries (i.e. O [2], Na [3], Si [5], Fe [8]), to the need of establishing a γ ray reference cross section able to perform several neutron inelastic cross section 48 7 measurements with very low uncertainties (< 5% for the for neutron induced reactions (i.e. Ti [6], Li [1]), and strongest transitions). We determined the γ production other topics of interest (level densities, neutrinoless ββ cross sections, the level cross sections and the total decay experiments and comparison with charged particle inelastic cross sections for nuclei from 7Li to 209Bi (see induced reactions). Refs. [1]-[13]). The reported data were unique in terms The experimental setup consists of the GAINS of neutron energy resolution and total relative spectrometer and a 235U fission chamber (see Fig. 1). uncertainty. However, there are some nuclei in which the transitions of interest are highly converted and conversion electrons are emitted instead of γ rays (e.g. 57Fe, 235U, 238U). For these cases, the (n, n'γ) procedure is unsiutable, so, a new experimental method should be investigated. This is one of the goals of the CHANDA task 8.3 in which we investigate the possibility of creating a setup to detect conversion electrons emitted from the neutron inelastic scattering reactions. While for the (n, n'γ) experiments we used the GAINS spectrometer, for the (n, n'e) measurements a completely new setup was designed and constructed, DELCO (Detection of ELectron from internal COnversion). This will be used for the first time in the first half of November, 2017 in an experiment approved by the EUFRAT PAC. The experiment together with the setup will be shortly described below. The talk will contain two main topics: i) a selection of results obtained using GELINA and GAINS in the Fig. 1 The GAINS spectrometer.

* Corresponding author: [email protected] 38

GAINS has up to 12 large volume HPGe detectors, with detectors (see Fig. 1 b). The samples were prepared by 4 detectors placed at 3 different angles 110o, 125o, 150o the JRC Geel target laboratory, using the molecular with respect to the neutron beam direction. The detectors plating deposition method on an Al backing foil of 0.025 have 100% relative efficiency and about 2.8 keV γ- mm thickness and a 1 mm Al ring with Dout=110 mm 60 energy resolution for the 1332 keV peak of Co. The and Din=100 mm. More characteristics of the samples are setup is placed at 100 m distance from the neutron displayed in Table 1. source which corresponds to a neutron energy resolution Sample 1 Sample 2 of 3 keV at 1 MeV and 88 keV at 10 MeV. We are using digital acquisition (ACQIRIS digitizers) with 12 bit Diameter (mm) 80.00 ± 0.02 80.00 ± 0.02 Mass (mg) 7.25 ± 0.05 7.04 ± 0.05 amplitude resolution (4096 channels) and 420 MS/s 2 (2.38 ns sampling frequency). The data is normalised Areal density (µg/cm ) 144.2 ± 1 140.0 ± 1 using the fission chamber [the 235U(n, f) cross section is Activity (Bq) 90.2 ± 0.6 87.5 ± 0.7 used as a reference]. Table 1. The characteristics of the two 238U samples. 3 Future (n, n'e) measurements The (n, n'e) experiments will also be performed at the References GELINA neutron source. The purpose is to construct the 1. M. Nyman, et al., Phys. Rev. C 93, 024610 total inelastic cross section by taking into account also (2016) the internal conversion contribution. The experimental 2. M. Boromiza, et al. EPJ Web of Conferences setup consists mainly of a reaction chamber under 146, 11015 (2017). vacuum, eight Si detectors [see Fig. 2 a) and b)]. 3. C. Rouki, et al., Nucl. Instrum. Methods Phys. DELCO will be placed in the measurement cabin located Res. A 672, 82 (2012) on flight path 1 at a distance of 30 m from the neutron 4. A. Olacel, et al., Phys. Rev. C 90, 034603, source. 2014) 5. A. Negret, et al., Phys. Rev. C 88, 034604 a) b) (2013) 6. A. Olacel, et al., Phys Rev. C 96, 014621 (2017) 7. L.C. Mihailescu, et al., Nucl. Phys. A 786, 1 (2007) 8. A. Negret, et al., Phys. Rev. C 90, 034602 (2014) 9. A. Negret, et al., Phys. Rev. C 96, 024620 (2017) 10. C. Rouki, et al., Phys. Rev. C 88, 054613 (2013) 11. A. Negret, et al., Phys. Rev. C 91, 064618 (2015) 12. L. C. Mihailescu, et al., Nucl. Instrum. Methods Phys. Res. A 531, 375 (2004) Fig. 2 a) The technical drawing of the experimental setup. b) A 13. L. C. Mihailescu, et al., Nucl. Phys. A 799, 1 zoom on the reaction chamber, detectors and 238U samples. (2008) The detectors have 50 nm dead layer, 100 µm thickness and 450 mm2 active area (see Fig 2). These detectors satisfy the need of good energy resolution in the energy range of interest, minimal X and γ-ray sensitivity and a maximum geometric efficiency. In order to obtain the best achievable energy resolution the detectors will be cooled down using two alcohol- based temperature control systems. Dedicated electronics will be used and the data will be acquired using TNT2 digitizers. Two measurements will be performed. In the first one we will measure the conversion electrons coming from the natural radioactivity of 238U. In the second measurement the target will be irradiated by the neutron beam. The aim is to detect the electrons emitted also due to the inelastic scattering of neutrons on the 238U samples. Two 238U samples (99.999%) will be placed back-to- back at 45o in respect to the beam direction, between the 39

Neutron inelastic scattering studies on 232Th : from measurements at GELINA to reactor applications

E. Party1,*, C. Borcea2, Ph. Dessagne1, X. Doligez3, G. Henning1, M. Kerveno1, A. Negret2,

M. Nyman4, A. Olacel2, A. Plompen4

1 Université de Strasbourg, CNRS, IPHC UMR 7178, Strasbourg, France

2 Horia Hulubei National Institute of Physics and Nuclear Engineering, Bucharest-Magurele, Romania

3 IPNO, CNRS-IN2P3/Univ., Paris Sud, France

4 European Commission, Joint Research Centre, Geel, Belgium

1 Introduction precise picture of the excitation of the 30 first energy levels of 232Th and provide valuable insights in (n,xn) In the frame of our CNRS-IPHC, IFIN-HH and EC-JRC- mechanism in the actinide region. Geel collaboration work at GELINA facility, that is (n,xn) reaction cross section measurement by way of prompt gamma spectroscopy coupled to time of flight measurements, results of the analysis relative to 232Th measurement campaigns are presented. 232Th is an important isotope to study because it is, along with 238U, the only abundant naturally occuring fertile material usable in innovant breeder reactor designs [1]. These designs are primarily fast neutron reactors, in which (n,xn) reactions are important. And the precision required on these cross sections for the construction of these reactors is a potent motive for our measurements. Fig.1. (n,n'γ) cross section for a 232Th 0+->2+ transition, in blue our experiment, in green previous experiment and in red theory predictions 2 232Th measurement at GELINA To measure (n,xn) reactions, we used the GRAPhEME 3 Cross sections sensitivities studies setup [2] (GeRmanium array for Actinides PrEcise MEasurements) installed at the flight path 16 - 30m of In complement to these measurements, we began, in GELINA facility neutron source. GRAPhEME was then collaboration with CNRS-IPNO, studies on slow neutron an array of 4 planar HPGe detectors with high energy thorium-fueled reactor parameters sensitivities to resolution on γ-rays emitted by (n,xn) reactions, and reaction cross sections, including measured (n,xn) ones. sensitivity to anisotropy of γ emission. Cross sections are Results have already been obtained for a thermal neutron normalized to 235U fission cross section, a fission reactor configuration using MCNP [3] and SERPENT chamber (235U deposit) giving us the neutron flux. Data [4] codes. These results are furthermore validated by have been gathered in the course of three different Total Monte Carlo method, which consists in running measurement campaigns, totalling more than 800 hours several calculations using a distribution of reaction cross of neutron beam. sections, taken from TENDL library [5], whose span Analysis is currently well advanced. More than 30 (n,n'γ) corresponds to the uncertainty on these reactions. In this cross sections have already been extracted (e.g. in Fig.1), study, both methods have yield similar results, which as well as 6 (n,2nγ) cross sections. In the near future, as confirms acurateness of sensitivities calculation. (n,xn) much as 55 (n,n'γ) cross sections and 10 (n,2nγ) cross reactions had small effects in this reactor configuration sections could be possibly extracted, presenting a very

* Corresponding author: [email protected] 40

as much of the physics comes from slow neutron reactions. Next step will be to reiterate this study with a fast neutron reactor configuration, where (n,xn) reactions are deemed to be more important.

4 Outlook of the presentation The presentation will start with a brief summary of the place of nuclear data in nuclear science applications and the specific needs for thorium. Then will follow explanations on the method of analysis, some highlights on encountered difficulties, and brief review of cross sections obtained. The last part will focus on sensitivities studies, which makes the link between the uncertainty of measured cross sections and the one of parameters in reactor physics.

References 1. Introduction of thorium in the nuclear fuel cycle short- to long- term considerations. Report 7224, Nuclear Energy Agency 2015. 2. M. Kerveno et al., Eur. Phys. J. A (2015) 51: 167 3. T. Goorley et al., "Initial MCNP6 Release Overview", Nuclear Technology, 180, pp 298-315 (Dec 2012) 4. J. Leppänen et al. (2015) "The Serpent Monte Carlo code: Status, development and applications in 2013." Ann. Nucl. Energy, 82 (2015) 142-150 5. A. J. Koning, D. Rochman, Modern Nuclear Data Evaluation with the TALYS Code System, Nuclear Data Sheets 113 (2012) 2841-2934

41

Nuclear Data for Criticality Safety Applications at IRSN

L. Leal1*, I. Duhamel1, N. Leclaire1, P. Schillebeeckx2, S. Kopecky2, A. Negret3, M. Nyman2, A. Olacel3, A. Plompen2

1Institut de Radioprotection et de Sûreté Nucléaire, BP 17 – 92262 Fontenay-aux-Roses Cedex, France

2European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Retieseweg 111, 2440 Geel, Belgium

3Horia Hulubei, National Institute for Physics and Nuclear Engineering, Reactorului 30, 077125 Bucharest-Măgurele, Romania

1 Background the transport equation requires the knowledge of nuclear constants, as for instance, the particle interaction cross- The Institut de Radioprotection et de Sûreté Nucléaire sections that give the probability of a particle-nucleus (IRSN) is the French public service expert in nuclear and interaction to occur. Therefore, the accuracy on the radiation risks with activities that cover all the related results of the calculation of a nuclear system is scientific and technical issues. IRSN provides expertise intimately related to the knowledge of the nuclear in support of radiation protection and nuclear safety constants, that is, how well the nuclear data as well as risks. their uncertainties are known. To exemplify the importance of the Geel Electron Linear The goal of the present document is to summarize the Accelerator (GELINA)1 in practical application two nuclear data needs for diverse applications within the examples for experimental data for the iron isotopes, IRSN complex. The results and conclusions are based on 54Fe and 56Fe, and 103Rh will be given. Following a short applications and examinations in connection to actual list of isotopes for which experimental data are needed nuclear systems. The design and operation of devices will be given. involving nuclear material requires the use of computer tools, modeling of nuclear system, and accurate understanding of the nuclear data involved in the 2 Introduction calculations. Regardless of whether the calculations are Neutron cross section data form the basis for any reactor performed for nuclear systems such as a nuclear reactor, physics or criticality calculation. The cross section shielding for radiation protection, criticality safety for represents the probability for a particle to interact with a material outside reactors, etc., the particle population given nuclide. It essentially describes how a neutron (neutron, charged particles, radiation gamma, etc.) are behaves when it moves through material. The selected determined on the basis of the solution of the transport nuclear data treatment is therefore essential to assure the equation. The two most common problems faced by a quality of the nuclear system calculations and nuclear engineer are to predict and control the system consequently impacting the results in connection to criticality, the so called Eigen-value problem, or to nuclear safety assessments. determine with a high degree of accuracy the particle source and intensity as well as the system particle There has recently been a renewed interest in nuclear spectrum. The latter problem is known as the fixed- energy to supply the demand for electricity. Reactor source problem. The tools frequently used are based on designs based on conventional and non-conventional stochastic centered Monte Carlo approaches or a concepts have been proposed as the new reactor deterministic solution of the transport equation. The generation. These new designs have heavily relied upon ever-increasing computational capabilities coupled with issues pertinent to reactor safety and also on the dealing refined techniques for the stochastic and deterministic with the nuclear waste. Nuclear data will play an solution of the transport equation permit to achieve more extremely significant role in these new reactor program accurate solutions for a nuclear system. The uncertainties and experimental facilities for performing data in connection with the modeling of the problem at hand measurements will certainly be the nuclear data provider are very small if not negligible. However, the solution of for the programs.

* Corresponding author: [email protected] 42

A resonance evaluation for 56Fe has been performed in Needs for better nuclear data are motivated by new the resolved resonance region up to 2 MeV.1 The upper reactor designs and concept as well as challenging issues energy limit of the present 56Fe evaluations in the nuclear in connection to criticality safety for materials outside data libraries is around the first inelastic level (846.753 reactor. Another interesting point to note is that keV). The new features in the present 56Fe evaluation are computer resources and nuclear code developments have the extension of the resonance energy region into the attained a high degree of dependability with low MeV region; use of R-matrix limited formalism (RML); resulting uncertainties associated to modeling and inclusion of inelastic channels in the resonance calculation methods. Therefore, the main source of evaluation; angular representation of the elastic and uncertainty is related to the nuclear data. inelastic cross-section data. The latter may be regarded as an option to replace the existing approach used in the Nuclear data needs arise in several fields as: ENDF that are based on Legendre moments given at a limited number of energies. - Source Term of Radiation and Heating - Decay Heat Calculation Among several data used in the evaluation the ‰ Fission Product & Minor Actinide Productions transmission measurements done at the RPI linear (Fission Product Yield, Activation) accelerator and the inelastic cross section data measured at GELINA played a major role. RPI provided three sets ‰ Decay Data of high-resolution transmission data taken at a flight- - Shielding Calculation for Fuel Cask path of 249.74 meters with sample thicknesses of 0.2728 ‰ Neutron and Gamma-ray Productions, (α,n) at/barns, 0.6532 at/barns, and 0.9251 at/barns, - Calculation on Re-criticality Potential respectively. GELINA data consisted of inelastic cross ‰ Neutron Production section covering the first inelastic channel up to 2 MeV. 2 - LWR Safety Foundation An example of the SAMMY fit of the RPI data and the ‰ Thermal scattering cross sections, S(α,β) inelastic data is shown in Fig. 1. The bottom curve corresponds to the inelastic data taken at GELINA, ‰ Resonance Data whereas the top curve is the total cross section extracted from the RPI transmission measurements. The solid line While the above listing exemplifies areas for which (red) is the SAMMY prediction using the resonance nuclear data are needed there is significant overlap on parameters whereas the symbol (black) is the the nuclear needs. This indicates the importance of the experimental data. use of nuclear data on diverse applications. The following section aims at providing a short listing of data needs for diverse applications at IRSN.

3 GELINA experimental data and evaluation for 54Fe, 56Fe and 103Rh

3.1. Resonance Evaluation for the 54Fe and 56Fe Isotopes In natural iron the abundance of isotopes 54Fe and 56Fe are 5.85% and 91.75%, respectively. Iron is extensively used in the nuclear system such as for instance as the structural material in thermal and fast reactors as part of the shipping cask for spent nuclear fuel assemblies, etc. Accurate nuclear data for the iron isotopes as for Fig. 1. SAMMY fit of the total cross section (extracted 54 56 from the transmission data) and the inelastic cross example the two isotopes, Fe and Fe, are needed for 56 improvement on the design and analysis of nuclear data section for Fe in the energy range 800 keV to 2 MeV. systems. It should be pointed out that the availability of the It is observed that the 54Fe and 56Fe isotopes show GELINA good resolution inelastic data allowed, for the first time, to perform an R-matrix evaluation to represent resonance like structures to energies as high as 2 MeV. 56 For practical applications a detailed representation of the the inelastic cross section for Fe. cross section as a function of energy is desirable for a Similarly, the extension of the resolved resonance region for 54Fe to 2 MeV requires the knowledge of the inelastic better calculation and interpretation of the effect of the 54 energy self-shielding in the cross section. Measurements cross section data. For Fe the inelastic cross section of the inelastic cross section for 54Fe and 56Fe have been becomes significant above 1408 keV. JRC/Geel in carried out at GELINA to help extending the resolved conjunction with IRSN is working on the development of an 54Fe evaluation up to 2 MeV. Work is underway at resonance evaluation up to 2 MeV. 54 GELINA to measure inelastic cross section for Fe. The 43

objective of the experiment is to deliver accurate data for for nuclear systems in the thermal and epithermal energy inelastic scattering of 54Fe using the (n,n’γ) technique region. However, for fast systems the uncertainty in the with the GAINS setup. The experiment aims for smaller cross section is much higher. Improvements of the 103Rh than 5% uncertainty for the 1408 keV transition from the capture cross section uncertainties in the fast region are first level to the ground state in the energy range where needed. IRSN has not investigated this issue. the cross section is at maximum. An enriched sample is used to maximize the number of levels from which a gamma-transition may be observed by minimizing interference with 56Fe. The level scheme shows no show- stoppers for excitation energy up to 4696 keV (the first tentative level), provided an energy range of Eγ=400- 3200 keV is covered, the cross sections are above 20 mb and the 54Fe mass is 20 g at 99% enrichment. The experimental inelastic data taken at GELINA will be incorporated in the SAMMY fitting procedure.

3.2 Resonance Evaluation for 103Rh

The 103Rh element is often encountered in nuclear reactors as a fission product. Accurate nuclear data for 103Rh isotope are needed in a wide energy range to account for applications such as criticality safety studies for transport casks, irradiated fuel storage and in reprocessing plant units for which the reduction in reactivity of configurations with spent nuclear fuel plays a major role (burn-up credit).

An effort has been taken at IRSN to re-evaluate the resolved resonance region for 103Rh including data uncertainty thru the covariance data. Transmission and capture cross section data taken at GELINA were used in Fig. 3: Uncertainty and the correlation in the 103Rh the evaluation. Figure 2 shows the results of the capture cross section. SAMMY fitting (red) compared to the experimental capture and transmission data taken at GELINA (black). Benchmark integral experiments for fission products, in particular 103Rh, have been carried out in France and the US. In the US the experiments were performed at the Sandia National Laboratory (SNL) whereas in France they were done at Valduc under the Fission Products (FP)3 and MIRTE4 program. Presently the results from the SNL experiments can be found in the International Criticality Safety benchmark Experiments Project (ICSBEP) Handbook5 under the description LEU- COMP-THERM-079. While IRSN researchers have access to the 103Rh MIRTE and FP experiments, nevertheless at the present time the benchmark are not available in the public domain.

Both IRSN and SNL experiments have been used to test the new 103Rh evaluation. The results indicate slight Fig. 2. SAMMY fit of the GELINA transmission and improvements with the new evaluation within the 103 capture yield for Rh in the energy range 4 keV to experimental uncertainty margins. Further improvements 6 keV. on the 103Rh can be achieved by using critical experiments with the neutron energy spectrum in the The uncertainty in the capture cross section due to the epithermal energy range sensitive to the 103Rh capture covariance data generated in the evaluation is displayed cross sections. IRSN and SNL envision performing new in Fig. 3. It should be noted that above 8 keV the experiments in the epithermal energy region using the covariance displayed in Fig. 3 is taken for evaluations SNL critical facility. Experimental analysis and design performed in the high energy region included in the Joint studies are in progress. European Fission and Fusion data library. One can observe form Fig. 3 that the uncertainty in the resonance region is acceptable for defining criticality safety margin 44

4 Nuclear Data Needs Listing 19F Measurements of Resonance Fluorine is elastic and and high encountered in In recent years there have been efforts for re-evaluating inelastic cross energy fuel enrichment cross-section. evaluation and fabrication nuclear data for several applications. While the Two inelastic process for evaluations have achieved a high degree of accuracy levels at 110 keV uranium fueled there are still needs for revision and evaluation. The and 196 keV reactor. nuclear data uncertainties have not followed the same Criticality safety pace as the data evaluation. In addition, new features applications related to the nuclear data needs for better accurate data for applications, such as criticality safety motivates the 28Si Transmission and Resonance Silicon is part of revision and re-evaluation of nuclear data. One key capture cross and high concrete used in 29Si section energy spent fuel matter in criticality safety prediction is the confidence in evaluation disposal the calculation results which is intimately associated to 30Si Silicon is also the criticality safety margins. It is of fundamental component of interest to the criticality safety practitioner to qualify and clays and argillites that are quantify the bias and associated uncertainties of the considered in nuclear system multiplication factor (keff) thru the use of some countries computational tools. Nevertheless, to achieve the desired as possible host accuracy on the calculation results, nuclear data, rocks for nuclear waste differential and integral, must be accurate. IRSN has disposal at great been engaged on effort to improve evaluated nuclear depth data and to develop specific tools for addressing issues Mo Several isotopes: Low energy Fuel fabrication, concerning criticality safety determination. As an isotopes new and resonance Experimental measurements for region reactors and example, nuclear data for low temperature as opposed to enriched samples criticality safety room temperature is deemed needed to ascertain nuclear issues criticality safety margins for system for which the needs (reprocessing for low temperature data exist. The Table below lists plant residue, burn-up credit some of isotopes for which nuclear data measurements for irradiated and evaluations are needed. fuel transport and storage) Isotopes Measurement Evaluation Application 103Rh No need of new Low energy, Criticality safety 239Pu Low energy data Resonance Pu solutions measurement resonance an studies for for determination and (reprocessing high energy transport casks 240Pu of eta shape. uncertainty plants); region or irradiated fuel Accurate application Reactor physics storage or in 241Pu measurements and criticality reprocessing safety plant units (use 233U Capture cross Resonance Reactor and fuel of Burn-up section region: cycle in credit) measurements resolved, connection to U- needed unresolved Th cycle; 206Pb New Resonance Sensitivity and high Spent fuel measurements are and high calculations energy storage analysis 207Pb needed in the energy indicate large uncertainties and design resonance region evaluation due to Lead. 235 208Pb U Total cross Low energy, Issues Reevaluation of section, alpha unresolved concerning natural lead (capture to fission Doppler- cross sections ratio) up 40 keV reactivity Table 1. Short isotope listing for data needs feedback

16O (n,α) cross section Measurement Issues with s above the discrepant 5 Conclusions threshold measurement energy of The paper points out the importance of data 2.354 MeV measurements activities carried out at GELINA for practical applications such as criticality safety, radiation protection, reactor analysis and design, etc. Examples of 45

the use of GELINA in resonance evaluation for the iron isotopes 54Fe and 56Fe, and for 103Rh have been given.

The importance of differential and integral data in evaluation process has been specified. The activities carried out at IRSN toward improvement of criticality safety predictions demand upgraded and well characterized nuclear data. Combined efforts of differential and integral data activities at IRSN provide the ground for producing improved nuclear data evaluations. A short listing of isotopes, as an example, for data nuclear needs for various applications is included in this paper

References

1. W. Mondelaers and P. Schillebeeckx, “GELINA, a neutron time-of-flight facility for high- resolution neutron data measurements'”, Notiziario Neutroni e Luce di Sincrotrone, vol. 11, pp. 19–25 (2006).

2. N. M. Larson, Updated Users’ Guide for SAMMY: Multi- level R-Matrix Fits to Neutron Data Using Bayes’s Equations, United States Department of Energy (2003).

3. N. Leclaire, T. Ivanova, E. Létang, E. Girault and J.F. Thro, Fission products experimental programme: validation and computational analysis, Nuclear Science & Engineering, volume 161, p:188- 215, 2009.

4. N. Leclaire, I. Duhamel, F.X. Le Dauphin, J.B. Briggs, J. Piot, M. Rennesson and A. Laville, The MIRTE experimental program: an opportunity to test structural materials in various configurations in thermal energy spectrum, Nuclear Science & Engineering, volume 178, p:429-445, 2014.

5. International Handbook of Evaluated Criticality Safety Benchmark Experiments, NEA/NSC/DOC(95)/01/1-IX, Organization for Economic Co-operation and Development (Nuclear Energy Agency (OECD-NEA), 2013).

46

Integral Benchmark Experiments on a Large Copper Block using GELINA accelerator to validate natCu neutron inelastic scattering cross sections from different neutron cross section databases.

M. Pillon1*, M. Angelone1, F. Moro1, D. Kim2, M. Nyman3, A. Plompen3

1 ENEA Department of Fusion and Nuclear Safety Technology, C.R. Frascati, via E. Fermi 45, 00044 Frascati (Rome) Italy 2 Department of Nuclear Engineering, Seoul National University 31-117, 1 Gwanak-ro, Gwanak-gu, Seoul 151-744, Korea 3 European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, B - 2440 Geel, Belgium

1 Introduction copper is present. Improving the quality of Cu data is thus of great importance. An integral benchmark experiment has Benchmarking of cross section data against integral been performed at neutron energy relevant to fusion (14 experiments is considered since the early days of neutronics MeV) at ENEA Frascati Neutron Generator (FNG) using studies a fundamental step which provides feed-back to the seven Cu plates with total dimension 60x60x70 cm3 and a evaluators for improving both the nuclear data and the total mass of 2.25 tons [7]. Reaction rates were measured nuclear models used to produce the nuclear data. In the field using different activation foils placed inside the Cu blocks. of fusion neutronics, benchmark experiments were carried The calculated quantities were then compared to the out in the USA since the 1980’s [1,2,3]. In the last 25 years experimental results in order to validate the data in Cu two laboratories were performing most of the fusion libraries. The experiment was complemented by oriented experiments (both benchmarks and mock-ups) with sensitivity/uncertainty analysis performed both using 14 MeV neutrons, namely the Fusion neutron source (FNS) deterministic and Monte Carlo SUSD3D and MCSEN in Japan (JAERI) and the Frascati neutron generator (FNG) codes, respectively. It may further be noted that JEFF-3.2 at ENEA Frascati (Italy). The novelty of the FNG and 3.3beta testing of copper data against the Frascati benchmark experiments, introduced since the 1990s, is in benchmark for 14 MeV and against critical benchmarks the extensive use of sensitivity and uncertainty analyses from the ICSBEP database revealed discrepancies that have applied both to the pre- and post-analyses of the not been resolved. This highlights the need for improved experimental configuration using deterministic and Monte data also for fission applications and hence for an Carlo based codes. SINBAD [4] is an international experiment with a fission-like neutron spectrum. It is collaboration to store, evaluate and share shielding possible to use the pulsed white neutron source GELINA at experiments that were made by different countries. A large JRC-Geel to perform shielding experiments within the part of these experiments are quite old and not all of them target hall. The neutron spectrum from GELINA is a fission have the sufficient quality assurance to be used for nuclear like spectrum similar to the fission neutron spectrum. The data evaluation. In addition, a large list of irradiated aim of the experiment presented here was the test and the materials in different neutron fields is desirable and validation of some recent nuclear data libraries (FENDL3.1; necessary. For this reason performing new shielding JEFF-3.3_T2; ENDF/B-7.1) by comparing MCNP-6 experiments is important. Copper is largely used in neutron transport calculation predictions of the activation tokamaks in heat sink components, magnets, diagnostics, response for a Cu block similar to that used at FNG. The microwave waveguides and mirrors. Only a few block used at GELINA was assembled using only six of the experiments, more than 20 years ago, have been performed seven plates used at FNG (dimensions 60x60x60 cm3) and so far with Cu in the neutron energy range relevant to was positioned at a distance of 100 cm from GELINA fusion: a measurement of leakage spectra, and an integral neutron target. experiment performed at the Fusion Neutron Source (FNS) facility in Japan (JAERI) [5,6]. 2 Cu benchmark experiment and results A lack of good quality data, like in the case of copper, 2.1. The GELINA neutron source and the target hall affects the analysis required for fusion applications. One of the main issues with ITER is with the uncertainty in the The Geel Electron LINear Accelerator Facility (GELINA) nuclear heating in the superconducting magnets where of the European Commission’s Directorate-General Joint

* Corresponding author: [email protected] 47

Research Centre (JRC) in Geel, Belgium, is a Time Of 2.2. MCNP calculation model & measurement Flight (TOF) facility especially designed and built for high- techniques resolution cross section measurements. It is a multi-user A detailed model of the GELINA neutron target, including facility, serving up to 12 different experiments the experimental hall and the copper block, was prepared simultaneously, and providing a pulsed white neutron for the MCNP6 neutron transport code. The activation foils source, with a neutron energy range between 1 meV and 20 were located in copper slots which, in turn, were positioned MeV. Neutrons are produced in bunches of less than 1 ns inside copper rods inserted in the assigned experimental duration, at repetition rates up to 800 Hz. The maximum 13 positions. These rods were also accurately described in the neutron yield is 3.2 × 10 neutrons/s. The GELINA MCNP6 model. Figs. 3 and 4 show details of the MCNP6 neutron-production target is a torus of depleted uranium, model. The MCNP neutron source term was provided in containing 10% molybdenum by weight. The pulsed tabular form, using 100 energy groups, by Pierre Leconte. It electron beam from the GELINA accelerator is hitting the was generated using MCNP5 code and ENDF/B-VII.1 cross target, and neutrons are produced by bremsstrahlung- section database, considering a mono-directional electron γ γ induced ( , xn) and ( , F) reactions. Cooling of the target is beam with homogeneously distributed energies from 70 to achieved by a flow of mercury through the target support 140 MeV, reaching a depleted uranium target. structure, and by helium flow around the torus. The experimental set-up and a general view of the target hall with the copper block in position are shown in Figs. 1 and 2 respectively. The shadow bars used to block the direct neutron flux from the target and thus allowing only the moderated neutron spectrum to be used in certain flight paths are clearly visible in the Fig. 3. The effect of these shadow bars and collimators on the present experiment was not investigated yet. When GELINA is not in operation, for radiation safety reasons, the rotating target is in a shielded position, well below the beam plane so that it is not visible in Fig. 2.

Fig. 3. MCNP cross sectional view of the experiment

Fig. 1. Experimental set-up CAD drawing.

TABLE I Activation Reactions and Decay Data. T1/2 is the product half-life, Eg the energy of the measured gamma-ray and Pg the emission probability per decay of the product nucleus. Isotopic Reaction T1/2 Eγ Pγ Abundance 103Rh(n,n')103Rh 100.0% 0.9 h 40 keV 0.068% 27Al(n,α)24Na 100.0% 14.96 h 1369 keV 100% 58Ni(n,p)58Co 68.27% 70.86 d 811 keV 99.45% 115In(n,n')115In 95.71% 4.49 h 336 keV 45.9% 56 56 Fe(n,p) Mn 91.72% 2.577 h 845 keV 98.87% Fig. 2. Photo of the target hall with the copper block in position

48

cross-section database, i.e. IRDFF-1.05, was used [9]. The other input for the codes was a trial neutron spectrum at the foils position, calculated with the MCNP model, including the copper block, as described above. Plots of the adjusted neutron spectra are shown in Fig. 5.

Fig. 4. MCNP model of rods with the flux monitors

The electrons produce high energy bremsstrahlung photons which generate neutrons by (γ,n), (γ,xn) and (γ,f) reactions. For this simulation, four types of particles have been used: electrons, positrons, gammas, and neutrons. Five different activation foils were used with threshold Fig. 5. Input and adjusted spectra from unfolding nuclear reactions as flux monitors, covering the energy range 0.04÷20 MeV, (Table I). For each material, a set of six foils (typical masses 1 gram/foil) was inserted in the 2.3. Results copper rods in the positions indicated in Fig. 4 and As said in the introduction, the calculations were carried out irradiated in a single run. using three different neutron transport cross section In total five irradiation runs were performed, the first libraries: FENDL3.1, JEFF33_T2 and ENDF7.1. The results devoted to the neutron spectrum and flux determination of the C/E comparisons are similar between the three using the unfolding technique as discussed later, the others libraries but JEFF33_T2 produces slightly better result. to irradiate the foils inside the block. Each set of materials Figure 6 shows the relative reaction rates at various were irradiated in a single run, except for aluminum and distances inside the copper block measured using the nickel foils which were irradiated and modelled together. different dosimeters while in Fig. 7 results of the C/E The duration of the irradiation was decided depending on comparisons using JEFF33_T2 library are shown. The the activation efficiency of the material under irradiation estimated uncertainties (one sigma) are also shown. (obtained with a pre-analysis of the experiment), while the The full comparison with all the libraries used will be accelerator neutron yield was kept practically constant. The discussed in the presentation. neutron yield of each run was however monitored using two monitors present in the target hall and the experimental results were normalized to the data from these monitors. At the end of the irradiation, the activated foils were measured using two calibrated HPGe detectors, one of them designed for low energy γ-ray and X-ray detection.

The first irradiation run was devoted to the determination of the neutron flux and spectrum impinging on the surface of the copper block facing the neutron target. The well-known neutron spectrum unfolding technique was used. Five foils of the same type as used inside the block were positioned on the front surface and in the center of the square copper block. This surface faces the neutron target. The foils were irradiated for one hour and measured with the HPGe detectors. The absolute activities at the end of the irradiation, normalized to disintegration per nucleus (dps), were used as input of two different unfolding codes, SAND- Fig. 6. The relative reaction rates at various distances inside the copper block measured using the different dosimeters. II and STAY_PNNL. Both codes were obtained from the IAEA-NDS databank [8] and the latest available dosimetry 49

Fig. 7 C/E comparison for all reactions using JEFF33_T2 library

References 1. R.T. Santoro,V. C. Baker, J.M. Barnes, Nucl. Techn. 37 (1978) 274 2. R.T. Santoro et. Al, Nucl. Sci. Eng. 80 (1982) 586 3. R.T. Santoro et. Al, Nucl. Sci. Eng. 84 (1983) 260 4. I. Kodeli, A. Milocco, Pedro Ortego and Enrico Sartori, 20 Years of SINBAD (Shielding Integral Benchmark Archive and Database), Progress in Nuclear Science and Technology, Volume 4 (2014) pp. 308-311 5. I. Murata, T. Nishio, T. Kondo, H. Takagi, O. Kokoo, A. N Takahashi, F. Maekawa, Y. Ikeda, H. Takeuchi, Neutron-nuclear data benchmark for copper and tungsten by slab assembly transmission experiments with DT neutrons, Fus. Eng. Des. 58-59 (2001) 617-621 6. C. Konno, F. Maekawa, Y. Oyama, Y. Ikeda, H. Maekawa, Benchmark experiment on copper with D-T neutrons for verification of neutron transport and related nuclear data of JENDL-3.1, Fus. Eng. Des. 28 (1995) 745-752 7. M. Angelone, D. Flammini, S. Loreti, F. Moro, M. Pillon, R. Villari, Copper benchmark experiment at the Frascati Neutron Generator for nuclear data validation, Fus. Eng. Des., July 27, 2015 in press. 8. https://www-nds.iaea.org/irdf2002/codes/index.htmlx 9. https://www-nds.iaea.org/IRDFFtest

50

Segmented mesh Micromegas and its associated electronics: development for a neutron beam profiler

M. Diakaki1,2, E. Berthoumieux1*, T. Papaevangelou1, F. Gunsing1,2, E. Dupont1, M. Kebbiri1, S. Anvar1, P. Sizun1, E. Monmarthe1, D. Desforge1, D. Jourde1, L. Tassan-Got2,3, L. Audouin3, E. Ferrer-Ribas1, J. Heyse4, P. Schillebeeckx4, C. Paradela4 and F. Belloni1,4

1 CEA Irfu, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France

2 European Organization for Nuclear Research (CERN), Switzerland

3 Institut de Physique Nucléaire, CNRS-IN2P3, Univ. Paris-Sud, Université Paris-Saclay, F-91406 Orsay Cedex, France

4 European Commission, Joint Research Centre, Geel, Retieseweg 111, B-2440 Geel, Belgium

1 Introduction Thanks to the etching technique the micromesh has been segmented into 60 strips in one direction, and the anode Measurements with neutron beams require a precise into 60 strips in the perpendicular direction. The detector knowledge of the neutron flux but also, especially when sensitive area is about 6x6 cm2. using samples smaller than the beam spot, its spatial For sake of simplicity the detector was operating with an distribution. The goal of the present work is to develop a Argon + 10% CH4 mixture that was available on site. standalone neutron beam profiler, as transparent as possible, in order to be able to keep this detector permanently in the beam, as a standard neutron beam monitor. A segmented mesh MicroMegas has been developed and used for the first time ever at the ~12 m GELINA capture flight path. This allowed to validate the detector conception and to revise its associated electronics.

2 Experimental set-up Fig.1. Schematic principle of a MicroMegas detector.

2.1. Detector description 2.2. Front-end electronics MicroMegas detector [1] is an ionizing gas system that A specific front-end electronic card (FEC) has been allows to have two well distinct operating zones, one developed in order to: between the cathode and the so-called “micromesh” - Distribute the high-voltage (or ground) on each (“drift region”) and one between the micromesh and the strip; anode (“amplification region”). A boron layer has been - Protect the electronic from sparkling; deposited on a thin aluminized mylar foil acting as - Send part of each strip signal to a dedicated cathode in order to convert neutrons into ionizing acquisition card; particles. In the drift region, the charged particle ionizes - Sum part of the remaining signal from each the gas and the moderate electric field in the order of a strip to perform neutron counting (using few hundred V/cm moves the electrons through the mesh GELINA’s standard acquisition chain) in to the amplification region. In this region a stronger parallel to spatial distribution. electric field, in the order of 100 kV/cm, creates an electron avalanche resulting in an easily detectable 2.3. Acquisition system for the spatial profile signal. The basic principle is shown in Fig.1. Microbulk technology [2] is based on kapton etching: a In standard MicroMegas detectors, i.e. without 50 µm thick foil of kapton with a thin layer (~5 µm) of segmented mesh, the mesh signal is used to trigger the copper on both sides is processed in order to create the acquisition. Because of the mesh segmentation such a MicroMegas structure. Holes are produced in one copper signal is no longer available, and so a self-triggering layer by chemical etching and then the underlying acquisition card based on the recently developed AGET kapton is removed. This results in a typical mesh-anode (Asic for General Electronic for TPC) [3] chip has been structure filled with gas and with the two parallel layers chosen to obtain the neutron beam profile. Each AGET separated by the remaining kapton pillars. Microbulk is chip is sampling the charge signal on a ~5µs time the key material for very flexible detector setups and window over 64 channels, allowing the readout for a configurations due to its use as a thin foil. time projection chamber (TPC).

* Corresponding author: [email protected] 51

are set to be sensitive to γ-rays. A peak appears every 1.25 ms corresponding to the 800 Hz accelerator repetition rate. By lowering the detector gain (bottom) the system become insensitive to the accelerator beam structure. The vertical line on the bottom part of Fig.3 corresponds to the dead time of the AGET system and is about 120 µs in average for this experiment.

Fig.2. A photo of the setup used for the test. See text for details. ~300

A picture of the detector mounted at the GELINA flight path can be found in Fig.2. The neutron beam first passes through an ionisation chamber (IC) used as a standard neutron flux detector before entering in the new neutron beam profiler (XY-MGAS). The acquisition card, called AsAd, contains 4 AGET chips and the whole electronic system was properly shielded and grounded. Fig.4. Sum signal amplitude spectra. Blue: raw spectra. Red: spectrum vetoed during “γ-flash”. Green: Expected spectrum. 3 Results The sum strip signal coming from the front-end card (FEC) was sent to a charge preamplifier (ORTEC 142B) and then included in the GELINA standard acquisition system after passing through a spectroscopic amplifier. With the present FEC this signal is extremely sensitive to the status of the AGET acquisition system. Fig.4 shows the sum amplitude spectra obtained with the AGET acquisition system switched-off. The blue curve shows the spectra without any condition applied. The red spectrum is obtained by rejecting short time-of-flight events. Finally, the green curve shows the expected counts, based on the IC and the expected mass of the boron target. Although the FEC card was bringing noise, Fig.4 shows that the detector resolution is as expected, thanks to the tuneable gain of MicroMegas detectors. 10 10 10 1 2 3 Nevertheless, it can also be seen that the counts in the spectra are about 300 times smaller than expected. After

10 10 − 1 visual inspection, it was found out that the B sample had shown a strong evolution with time, and it was clearly visible that most of the deposit had disappeared. To keep a reasonable measuring time the cathode was replaced by a 235 µg/cm2 boron sample available on site.

1 Fig.5 shows the neutron beam image with a cadmium event interval (ms) event time

RMS RMS Mean Entries foil covering part of the detector. The image is obtained HInt 1256133 0.3789 0.293 by plotting the last recorded strip for each event on both the anode (in horizontal axis) and mesh (in vertical axis) plane. The last recorded strip corresponds to the Fig.3. Interval time spectra between 2 consecutive events in electrons generated closest to the cathode, where the two different working regimes. See text for explanations. neutrons interact with 10B sample. The missing strips signals were due to a wrong mapping on the Front End Thanks to its high versatility it is possible with a Electronics card. MicroMegas to be sensitive or not to gamma-rays, by acting on the mesh voltage. Fig.3 shows the interval time events between two consecutive events from the self- triggering AGET acquisition system, in two different working conditions. The top part of the figure illustrates the case when the detector high-voltage and thresholds 52

3. E.C. Pollacco et al., Physics Procedia 37, pp 1799- 1804 (2012). https://doi.org/10.1016/j.phpro.2012.02.506 4. E. Berthoumieux et al., “XY-MicroMegas Neutron Detector Tests & Results”, GET Meeting, Saclay 29/01/2015 5. M. Diakaki et al., “Status of the XY-MGAS detector”, n_TOF Analysis Meeting, CERN 25- 27/02/2015 6. F. Gunsing, “Des neutrons en plein vol à n_TOF au CERN”, Assemblée Générale Irfu, Saclay 03/03/2015 7. M. Diakaki et al., “A new transparent XY- MicroMegas neutron beam profiler”, RD51 collaboration meeting & 2nd special workshop on neutron detection with MPGDs, CERN 16- Fig.5. Neutron beam image with a Cd foil covering part of the 17/03/2015 detector. 8. F. Gunsing et al., “Support to NFS and n_TOF The deposited energy spectra on the anode plane equipment”, Joint JEFF-CHANDA Workshop on reconstructed by software summing of each strip signal Nuclear Data Measurements, Paris 27-30/04/2015. amplitude is very similar to the one shown on Fig.4, 9. E. Berthoumieux et al., “Revue de projet n_TOF”, while the one on the mesh plane showed a worse energy Saclay 19/10/2015 resolution. This loss in resolution on mesh signals was due to a channel per channel gain variation on the AGET acquisition board when dealing with positive polarity signals.

3 Conclusion and outcome

A segmented mesh MicroMegas has been used for the first time ever on an experiment in order to extract the neutron beam profile. Thanks to its high versatility the detection system can be tuned to be sensitive or not to γ- rays. This is of primary importance when using a self- triggered acquisition system. This test performed at GELINA has shown that the detector was working perfectly. On the contrary, several issues were found on the front end electronics side and on the acquisition system. Thanks to this measurement, new electronic cards were designed, one per functionality instead of a single complex one. The issues on the acquisition system were also clearly identified and solved. The outcome from this test was presented in several meetings [4-9]. Such a system is now routinely used at n_TOF to measure the beam profile. To overcome the sensitivity of the sum signal to the AGET acquisition system status, the signal for neutron counting is now taken from the cathode. This allows to have a completely independent signal that could also be used to trigger the acquisition system devoted to the beam profile measurement. A bigger, 10x10 cm2, version of a segmented mesh micobulk MicroMegas with 128 strips in each direction is presently under construction.

References

1. I. Giomatris et al., Nucl. Instrum. Meth. A376 29-35 (1996). 2. S. Andriamonje et al., Journal of Instrumentation 5 P02001 (2010). 53

Characterisation of Bi-samples by Neutron Resonance Capture Analysis

1,* 1 2 1 2 1 1 Antonín Krása , Peter Baeten , Jan Heyse , Anatoly Kochetkov , Stefan Kopecky , Nadia Messaoudi , Alexey Stankovskiy , Gert Van den Eynde1, Carlos Paradela2, Peter Schillebeeckx2, Guido Vittiglio1, and Jan Wagemans1

1 Belgian Nuclear Research Centre SCK•CEN, Mol, 2400, Belgium

2 Joint Research Centre, Geel, 2440, Belgium

1 Integral experiments for Bi data Bi plate validation at the VENUS-F reactor U rod Integral experiments for nuclear data validation are Bi rod being carried out at the fast VENUS-F zero-power Al2O3 rod reactor of the Belgian Nuclear Research Center SCK•CEN in Mol (Belgium) [1]. VENUS-F serves as a mockup of MYRRHA [2], which will be a fast accelerator driven system using lead-bismuth eutectic as SS casing coolant and spallation target.

In 2016, experimental campaign for bismuth Fig.2. VENUS-F fuel assembly consisting of U+Bi+Al2O3 rods nuclear data validation was performed. In total 625 kg of + Bi plates in a stainless steel (SS) casing. Side length is 8 cm. Bi was loaded in fuel assemblies, see Fig.1 and Fig.2. The main focus was on the neutron energy region from 100 eV up to 10 MeV, see Fig.3. Preliminary sensitivity and uncertainty analysis of nuclear data performed with the SANDY code [3] indicates significant sensitivity of the effective multiplication factor of the VENUS-F core mainly to the 209Bi inelastic scattering cross-section, and to a lesser extent to the elastic scattering and the capture cross- sections.

reactor vessel

Pb reflector

CR2 SR3 SR4 SS casing for 12×12 lattice SR2 SR5 U/Bi fuel Fig.3. Neutron cross-section data on bismuth from the JEFF- 3.1.2 library (left-hand side axis) compared with the neutron assembly

rod SR1 SR6 spectrum (right-hand side axis) in the active zone of the drop safety rod VENUS-F reactor. CR1 control rod exp. channel

Fig.1. VENUS-F critical core with bismuth in fuel assemblies. The vessel diameter is 160 cm.

* Corresponding author: [email protected] 54

2 Bi samples determine the elemental and isotopic composition of materials. For these experiments, high-purity (99.99 %) bismuth Several Bi samples used for the measurements at rods and plates (Fig.2) were used. The Bi-material was VENUS-F were re-shaped to be compatible with the characterized with inductively coupled plasma mass beam size at the sample position of the measurement spectrometry (ICP-MS) by the supplier (EVOCHEM) , station. That was possible using the Bi plates (not the Bi see Table 1. rods). All measurements were carried out with the At SCK•CEN a sample of a Bi rod was accelerator operating at 800 Hz using a 1 mm-thick Cd investigated with neutron activation analysis (NAA). For overlap filter. A fixed S-filter and Na filter were used to some elements with a relatively high probability for monitor the background. neutron absorption (e.g. Ag, As, Cu) a substantial Several Bi samples were irradiated at the 12.9 m difference between the certified and the measured values capture station of flight path 5 of GELINA (2 days of is observed, see Table 1. It has been seen in recent irradiation per sample). The prompt γ-rays originating experiments at VENUS-F loaded with lead that such from a capture reaction in the samples were detected by impurities caused non-negligible distortions especially in C6D6-based liquid scintillators (NE230) of 10 cm the fission rate spatial distributions [1]. diameter and 7.5 cm length. The total energy detection principle in combination Table 1. Elemental analysis of Bi. The data measured with with the pulse height weighting technique is applied to ICP-MS refer to the composition of the batch of Bi material. make the detection efficiency for a capture event directly The data measured with NAA refer to a Bi rod. The proportional to the total γ-ray energy available in the uncertainties are given at 2σ. capture event [5]. The shape of the neutron spectrum was Method NAA ICP-MS measured in parallel with a 10B Frisch gridded ionization performed by SCK∙CEN EvoChem chamber placed at about 80 cm in front of the sample. Isotope Content [ppm] From the results of the neutron flux measurements and the response of the capture detection system, a Mg 0.5 capture yield is deduced, see Fig.4. It shows clear Al 0.5 resonance structures at 5.2 eV and 800 eV due to the Cl 4.3 ± 1.0 presence of Ag and Bi, respectively. K 0.63 ± 0.04 Additionally, Ag foils with a known areal density Ca 1 (99.97 % purity, 8 µm thick) were irradiated together with Bi samples. The fit of the Ag peak counts in case of Sc 0.009 ± 0.001 a simple Bi sample and a stack of Bi samples+Ag foils V 0.025 ± 0.004 (Fig.5) enables determining the absolute content of Ag Mn 0.52 ± 0.03 in the Bi samples. Fe 0.5 A preliminary analysis of this data suggests that the Ni 0.2 relative weight of Ag in the Bi plate is (30±5) ppm, which is definitely more than the 0.5 ppm declared by Cu 4.4 ± 0.2 0.5 the provider (for the entire batch of material). As a next As 0.005 ± 0.001 0.1 step, NAA will be also applied to a sample of the Bi Ag 7.32 ± 0.34 0.5 plate that was analyzed using NRCA. Cd 0.2 In 0.006 ± 0.001 0.15 Sn 0.5 Sb 0.4 800 eV La 0.0037 ± 0.0004 5.2 eV W 0.024 ± 0.001 0.10 Au 0.027 ± 0.001 Pb 0.5

3 NRCA at GELINA 0.05 Experimental yield Experimental To solve this issue with discrepant elemental composition, the verification of the relative amount of these elements using the neutron resonance capture 0.00 analysis (NRCA) through the EUFRAT program was 100 101 102 103 proposed. This technique is available at the time-of- Neutron energy / eV flight facility GELINA of JRC in Geel, Belgium. Fig.4. Experimental capture yield as a function of neutron The NRCA method [4] uses the presence of energy from the neutron resonance capture analysis of Bi plates resonances in neutron induced reaction cross sections to at the GELINA facility.

55

BI - Ag - Bi 1 10 Fit Bi-sample (homogeneous Ag distrirbution)

100 Counts

10-1

10-2 10-7 10-6 10-5 10-4 10-3 Areal density / (at/b) Fig.5. Fit of the measured counts corresponding to the 5.2 eV peak of Ag as a function of the sample areal density. The measurements of the Bi sample itself and a stack of Bi samples combined with Ag foils of known areal density are shown.

4 Conclusion

It has been noticed that a provider's assessment of the elemental composition of materials used in validation experiments can be unreliable. Follow-on verification studies are important when the impurities have a significant impact on parameters of interest. Complementary analysis methods including standard neutron activation analysis, mass spectrometry and more advanced methods like neutron resonance capture analysis (available at the GELINA facility of the EC Joint Research Centre) are useful tools for that purpose.

References

1. A. Kochetkov et al., “The Lead-Based VENUS-F Facility: Status of the FREYA Project”, EPJ Web of Conferences 106, 06004 (2016). 2. G. Van den Eynde et al., “An updated core design for the multi-purpose irradiation facility MYRRHA”, J. Nucl. Sci. Technol. (2015). Available online http://dx.doi.org/10.1080/00223131.2015.1026860 3. L. Fiorito et al., “Nuclear data uncertainty propagation to integral responses using SANDY,” Annals of Nuclear Energy 101 (2017) 359–366. 4. P. Schillebeeckx et al., “Neutron Resonance Spectroscopy for the characterisation of materials and objects.”, Report EUR 26848 EN 5. A. Borella, G. Aerts, F. Gunsing, M. Moxon, P. Schillebeeckx, R. Wynants, Nucl. Instrum. Methods A 577, 626 (2007).

56

Epithermal/fast Neutron beam monitoring at GELINA time-of-flight facilty using Uranium-coated single crystal diamond detector

S. Fiore *a, E. De Luciab, J. Heysec, P. Schillebeeckxc, G. Alaertsc, A. Pietropaoloa

aENEA, Department of Fusion and Technology for Nuclear Safety and Security, Italy bINFN Laboratori Nazionali di Frascati, Italy cJoint Research Centre - JRC , Geel, Belgium

Introduction 1. Experimental setup

The described experiment was performed at the GELINA neutron time-of-flight facility of the Joint Reseach Centre (JRC) in Geel, Belgium. Localized characterization of neutron beams is very useful for a number of applications. The knowledge of the intensity Flight path 2 of the GELINA facility has been used, with distribution of epithermal neutrons (in the range between 400 neutrons originating from the target travel 8.70 +/- 0.05 m meV and 200 keV) at the exact sample position allows to before reaching our detector. The inter-bunch time of the make quantitative analysis of the elemental composition of a electron beam was 20 ms, so that the travel time of the neutrons material during Neutron Resonance Capture Analysis (NRCA) to the detector through the flight path allowed to distinguish investigation. In beam monitoring, the knowledge of the between neutrons with energy greater than 1 meV. Slower spectral fluence rate at the irradiation point within a few square neutrons would reach the detector piled up with the faster ones millimeters area may provide information on the level of from the subsequent bunches: for this reason, neutron energy homogeneity of the beam, evidencing the di↵erences between measurement through time-of-flight (TOF) has been performed umbra and penumbra of the beam spot at the measurement with a Cadmium filter to cut o↵ the slower part of the neutron position. spectrum. As far as fast neutrons are concerned, the localized measure- ment of the neutron flux is very important in the measurement of the Single Event E↵ect cross sections of electronic compo- 235U layer Al contact nents whose quantitative estimation depends on the knowledge of the local neutron flux over the irradiation area covered by SCD the component. The standard beam monitors, typically used at beam lines operating at spallation or photo-production neutron sources, HPHT-Diamond B-doped are generally based on Li-loaded scintillators, sensitive to some extent to gamma radiation background always present in neutron environments [1, 2]. The e↵ective use of Single Crystal Diamond (SCD) detec- tors for thermal, epithermal and fast neutron monitoring at spallation neutron source was already assessed in di↵erent Figure 1: schematic structure of the diamond detector used in the measurements experimental papers [1, 3, 4], as well as their use for 14 MeV fusion neutrons for burning plasma diagnostics [5, 6]. Figure 1 shows the schematic structure of the SCD detec- In this experimental work, the use of SCD for localized ther- tor. The diamond used for the tests was grown as a small sin- mal/epithermal neutron beam monitoring at a photo-production gle crystal by microwave chemical vapor deposition. A highly neutron source is investigated to assess the potential of such conductive boron-doped diamond film of 20 mm thickness is detection device in an environment where gamma-ray fluxes first grown epitaxially on a 44 mm2 commercial high pressure- are as intense as neutron fluxes. high temperature (HPHT) diamond substrate. This B-doped layer is used as a back contact. The 25 mm thick intrinsic di- amond layer is then grown on the doped surface in a separate clean reactor,in order to avoid boron contamination of the in- trinsic layer. After the growth,the intrinsic diamond layer is ⇤Corresponding author oxidized by isothermal annealing at 500C for 1 hour in air, in

Preprint submitted to Elsevier October 13, 2017 57

order to remove the H2 surface conductive layer. On top of the By converting the TOF values to the corresponding neutron layered diamond structure, a 2.5 mm diameter, 100 nm-thick energies, the spectrum in Fig. 2 (red curve) has been obtained. aluminum layer is thermally deposited and used as top con- The comparison with the expected energy-dependent cross sec- tact. The SDD structure acts as a p-type/intrinsic/metal Schot- tion spectrum is also shown in blue curve. tky Barrier Diode. The aluminum contact creates a Schottky The charge collected in the diamond detector was also ac- junction with the intrinsic diamond that,in turn, is the detec- quired event by event. This charge corresponds to the energy tor layer sensitive to the ionizing radiation (drift-layer). The deposited in the diamond by the induced Uranium fission frag- SDDs B-doped layer acts as a p-type layer (hole injector) and ments. The energy spectrum in Fig. 3 shows the typical neutron determines the unipolarity of the device under direct polariza- induced fission spectrum that features a Q-value of about 200 tion. The device operates in reverse biased mode, with a pos- MeV . itive voltage applied to the top metal contact and a grounded B-doped contact.The electric field in the drift layer is in the or- der of 2E4 V/cm. Electronhole pairs generated in the diamond are then collected at the contacts, provided that the diamond 50000 quality is such that recombination and capture (trapping) are negligible. The intrinsic time response of the detector is in the 40000 order of 1 ns and it is well suited for timing applications like time of flight neutron spectroscopy[3, 4]. 30000 The diamond detector was placed on the transverse plane with respect to the neutron beam direction. A movable support 20000 allowed the horizontal scan of the beam along its axis. The sig- nal was read out through an Ortec 142A preamplifier, then sent 10000 to an Ortec 572 amplifier located in the same experimental hall, 0 2 m away from the detector. Data acquisition was performed 0 100 200 300 400 500 600 700 800 900 1000 through a custom-made system built by ERC Geel: DAQ-2000, Fragments energy (a.u.) which allowed to acquire both TOF and charge deposited in the detector. A T0 signal synced with the electron beam pulses was Figure 3: Energy deposited by U fragments in the diamond detector used as a start for the TOF measurements. In Figure 4 the fragment energy as a function of the TOF is reported: no correlation is present between the two quantities 2. Data acquisition and analysis as expected. In order to measure the TOF of the detected neutrons, a Cad- mium foil of 1 mm was put in front of the neutron beam exit 1000 to cut o↵ the slower part of the beam. This allowed to have 900 a sub cadmium cuto↵ neutron absorption close to 100%. The diamond detector was centered on the beam, and a long data 800 acquisition run of 24 h was carried out in order to acquire su- 700 cient statistics. 600 Fragments energy (a.u.) 500

400

B 300

200 800 100

3 0 ×10 0 50 100 150 200 250 time of flight (a.u.) Yield 400 Figure 4: Deposited fragments energy vs time of flight

Once the TOF measurements shown the good performances of the U-diamond detector, an horizontal beam scan was per- 0 0 5 10 15 20 25 formed by moving the detector through the precision rail Neutron energy / eV mounted at the bottom of the support. This rail allowed the detector to be moved across +/- 5 cm with a precision of +/- 0.1 mm . In order to increase the incident neutron rate, the Cad- Figure 2: Incident neutron energy obtained by time of flight (red) compared mium foil was removed. A significant change in the neutron with neutron-Uranium cross section (blue) energy spectrum across the beam spot was not expected, based 2 58

on previous measurements and Monte Carlo simulations by the GELINA group, so even if the single neutron energy could not be measured, the energy distribution was assumed to be un- changed across the beam spot. Data were recorded with 2-hour runs in each position, moving the detector in steps of 2 mm. The neutron rate was measured in each position, and a beam profile has been measured.

References

[1] A. Pietropaolo, G. Verona Rinati, C. Verona, E.M. Schooneveld, M. An- gelone, M. Pillon, Nucl. Instr. Meth. A 610, 677 (2009). [2] R. Pilotti, M. Angelone, M. Marinelli, E. Milani, G. Verona-Rinati, C. Verona, G. Prestopino, R. M. Montereali, M. A. Vincenti, E. M. Schoon- eveld, A. Scherillo, and A. Pietropaolo, Europhys. Lett. 116 (2016) 42001. [3] A. Pietropaolo, C. Andreani, M. Rebai, L. Giacomelli, G. Gorini, E. Perelli Cippo, M. Tardocchi, A. Fazzi, G. Verona Rinati, C. Verona, M. Marinelli, E. Milani, C. D. Frost and E. M. Schooneveld, Europhys. Lett, 92, 68003 (2010). [4] 68. A. Pietropaolo, C. Andreani, M. Rebai, L. Giacomelli, G. Gorini, E. Perelli Cippo, M. Tardocchi, A. Fazzi, G. Verona Rinati, C. Verona, Marco Marinelli, E. Milani, C. D. Frost and E. M. Schooneveld, Euro- phys. Lett. 94, 62001 (2011). [5] Angelone M., Fonnesu N., Pillon M., Prestopino, G., Sarto F., Milani E., Marinelli M., Verona C. and Verona-Rinati G., IEEE Trans. Nucl. Sci., 58 (2011) 1141. [6] Pilotti R. et al., J. Instrum., 11 (2016) C06008.

3 59

Investigation of Nuclear Fission thanks to EC-JRC Geel facilities

Olivier Serot1,*

1 CEA, DEN, DER, SPRC, Cadarache, F-13108 Saint-Paul-lez-Durance, France

A better knowledge of nuclear data with target accuracy particles, energies released in fission,…) and on the is required by the nuclear industry for operational and other hand, at investigating correlations between those future nuclear installations. In order to satisfy these fission observables. Hence, it is possible to access requirements, CEA-Cadarache has developed a strategy nuclear data useful for both nuclear reactor applications based on three complementary aspects: (i) and our understanding of the fission process. In order to implementation of new microscopic measurements test and improve nuclear models implemented into the (which can be done within the EUFRAT program) code, experimental data provided by JRC-Geel are benefiting from advances in nuclear detection extremely important and useful. technology, with a mastery as good as possible of the experimental uncertainties; (ii) use of integral 2.1. Pre-neutron data experiments for data assimilation and adjustments; (iii) development of new calculation capabilities, based on The pre-neutron mass and kinetic energy distributions more physical grounds, precise enough to reach are a prerequisite to start a FIFRELIN calculation. These acceptable accuracy for the nuclear data evaluation. The data, usually obtained from a 2E-experiment [5], are points (i) and (iii) are illustrated here for data related to therefore highly desirable. When no experimental data nuclear fission where requirements are still numerous are available, we use data provided by the GEF code [6]. and where strong efforts are still needed to improve our The sensibility of these input data on the calculated knowledge of the fission process. The presentation will fission observables will be shown. be subdivided into three main parts.

2.2. Prompt Fission Gamma 1 Fission Cross Section

235 Since 2007, in response to a ‘High Priority Request List’ U is the most common fissile nuclide worldwide published through the OECD/NEA [7], many studies exploited. Its neutron-induced fission cross-section σnf from both experimental [8] and theoretical sides [9-10] highly influences results from numerical simulations. have been undertaken. This very nice example of σ Experimental measurements of nf below a hundred of symbiosis between nuclear reactor needs, keV are seldom and relatively ancient especially in the experimentalists and theoreticians has led to new thermal energy range. At the Linear Accelerator of JRC- evaluations of the prompt gamma fission spectra and Geel, we plan to conduct new experimental campaigns. multiplicities, which were integrated into the recent To reduce systematic uncertainties, several JEFF-3.3 library [11]. An overview of these ten years of measurements under different experimental conditions effort will be given as well as the contribution of these will be carried out from thermal region to a hundred of experimental data on the theoretical models. keV. We hope to both resolve discrepancies between existing data sets [1] and reduce the uncertainties of the cross section itself. The obtained results should allow us 2.3. Prompt Fission Neutrons to improve evaluated nuclear data libraries. The prompt fission neutron characteristics (spectra, multiplicity, neutron emission probability …) and their 2 Fission Observables correlations with other fission observables (total kinetic energy and mass of the fission fragments,…) are of great The ‘FIFRELIN’ Monte-Carlo code [2-4], developed importance for validating fission models. As an example, recently at CEA-Cadarache aims, on one hand, at the average prompt neutron multiplicity as a function of calculating post-neutron fission observables (spectra and mass (saw-tooth curve) and its evolution with the multiplicities of the prompt neutron and gamma incident neutron energy provides information on the

* Corresponding author: [email protected] 60

deformation of the fission fragments at the scission point and how the available excitation energy is shared between the two fragments. Other examples of a comparison between JRC-Geel experimental data [12] and FIFRELIN calculations will be discussed.

3 Ternary tritium emission probabilities Ternary tritium production from fast neutron induced fission reaction is needed for GEN-IV reactors and in particular for the future ASTRID reactor. Indeed, the uncertainty on the amount of tritium produced in the reactor core and transferred into the secondary circuit has a great economic impact. Due to the low probability of the ternary fission process and the low fission cross section, measurement of tritium production from fast neutron induced ternary fission is very challenging [13]. In the past [14], by comparing spontaneous fission and thermal neutron induced fission, the impact of the compound nucleus excitation energy on the ternary 4He and 3H emission probabilities were investigated, showing a surprising different behavior for these ternary particles. This should be confirmed by exploring a possible experiment on MONNET facility.

References 1. C. Paradela et al., EPJ Web of Conferences 111, 022003 (2016) 2. O. Litaize and O. Serot, Phys. Rev. C 82, 054616 (2010) 3. O. Litaize, et al., Eur. Phys. Journ. A 51 (2015) 177 4. D. Regnier, et al., Comput. Phys. Commun. 201, 19–28 (2016) 5. A. Gook et al., Phys. Rev. C 90, 064611 (2014) 6. K.-H. Schmidt et al., Nucl. Data Sheets 131, 107 (2016) 7. G. Rimpault et al., http://www.oecd- nea.org/dbdata/hprl/tmp/HPRLgammafission.pdf 8. C. Gatera et al., Phys. Rev. C 95, 064609 (2017) and references therein 9. P. Talou et al., Phys. Rev. C 94, 064613 (2016) and references therein 10. R. Vogt and J. Randrup, Phys. Rev. C 87, 044602 (2013) and references therein 11. O. Serot et al., JEF/doc 1828, NEA Report, 2017 12. F.-J. Hambsch et al., EPJ Web of Conferences 122, 01005 (2016) and references therein 13. L. V. Drapchinskii et al., Jour. of Nucl. Energy Parts A/B. Vol. 19. pp. 69 to 71 (1965) 14. O. Serot et al., AIP Conference Proceedings 769, 857 (2005) 61

Experiments on ν A)(

A. Al-Adili 1,*, D. Tarrío 1, F.-J. Hambsch 2, A. Göök 2, K. Jansson 1, S. Oberstedt 2, V. Rakopoulos 1, A. Solders 1 and S. Pomp 1

1 Division of Applied Nuclear Physics – Department of Physics and Astronomy Uppsala University - Uppsala, Sweden

2 European Commission - Joint Research Centre, Directorate G, Geel, Belgium

1 Background 2 Experiments Studies of the energy-dependence of ̅ are important for a successful modelling of nuclear fission. In The measurements were performed at the former Van de particular, it infers how the excitation energy is shared Graaff of JRC-Geel. The experimental setup is depicted between the fission fragments (FF) at scission. Various in Fig. 1. The quasi-mono-energetic beam was produced theoretical models and experimental analyses have via the 7Li(p,n) reaction yielding 0.5 MeV neutrons. assumed different trends in ̅ as excitation energy About 1 dm of paraffin was then used to moderate the increases [1]. The main divergence seems to be that fast beam to thermal energies. Two ND’s were located some assume an increased ̅ only for heavy axially to the FGIC. The FGIC provides the emission fragments while others presume an average increase in angles and the kinetic energies of the two fragments, the whole shape [2]. which are used to calculate the pre-neutron emission mass distributions. The Time-Of-Flight (TOF) of the This project aims at systematic measurements of ̅ neutrons was derived from the FGIC cathode signal and as a function of incident neutron energy, En. The the neutron detector signal with a resolution of FWHM = experiments serve mainly for fission-code development 1.3 ns [4]. Prompt fission neutrons were separated from but will also enhance the accuracy of fission-yield data prompt fission gamma-rays by means of pulse-shape for applications. Our plan is to apply two independent discrimination. Fully digital acquisition systems were techniques to investigate the average neutron emission; employed and the triggering system was set on the 2E method + neutron detectors (ND) and the 2E-2v coincidences between the FGIC and ND’s. In addition, method (See Ref. [3] for our work on the VERDI the rate of non-coincident events was also recorded, to spectrometer). This paper presents a feasibility test using provide a means of measuring ̅ as the ratio between the 2E method via a Frisch-Grid Ionization Chamber events with and without neutron and fission fragment (FGIC). As a first step we measured the 252Cf(sf) and 235 coincidence. U(nth,f) reactions at the JRC-Geel.

252 Fig.2. The Cf(sf) neutron spectrum, measured in the two Fig.1. The FGIC and one of the two neutron detectors. The 252 235 ND (full black and dotted red lines). The Mannhart evaluation Cf(sf) and U(nth,f) reactions were measured. (dashed green line) is used to estimate the internal detector efficiency (blue dash-dots, right axis).

* Corresponding author: [email protected] 62

Conservation of mass and momentum is exploited, Acknowledgements utilizing input ̅ data from Ref. [5]. Normalization was done for the solid angle, total fission rate and for the The Uppsala group is indebted to EUFRAT for their total number of emitted neutrons. support in providing beam-time and financial support. CHANDA is also acknowledged for their scientific visit grants. 3 Results After applying all necessary cuts, the resulting neutron TOF is converted to energy, seen in Fig 2. The two neutron-detector results are plotted in black and red, together with the Mannhart evaluation [4]. The ratio to the evaluated spectrum is taken as detector efficiency curve for the respective detector (plotted for one ND in blue). The measured mass yield of 252Cf(sf) is plotted in Fig. 3. The mass distributions resulting from (sample side in blue and backing side in red). The average distribution (in green) agrees well with the literature data but shows slightly worse mass resolution. Fig. 4 shows ̅ in red, compared to the reference in black [5]. Fig.4. The measured prompt fission neutron multiplicity for Overall, the agreement is good. The ̅ is also 252Cf(sf), as a function of fragment mass. shown in Fig. 5 and exhibits a slope very similar to Ref. [5].

This experiment serves as a proof-of-principle and the results were satisfactory. Preliminary results on 235 U(nth,f) show satisfying agreement with the Wahl systematics, however counting statistics is an issue which affects the quality of the correction steps. In addition, a large background of γ-rays (from neutron capture in the shielding paraffin) in the ND’s complicates the separation between neutrons and gammas.

4 Outlook Fig.5. The measured prompt fission neutron multiplicity for 252Cf(sf), as a function of the fragment’s TKE. A new experimental proposal was accepted at En=5.5 MeV. A main challenge will be to discriminate the fission neutrons from in-beam and back-scattered neutrons. Simulations are currently performed to References optimize the experimental setup for this harsh neutron 1. A. Al-Adili, F.-J. Hambsch, S. Pomp, environment. S. Oberstedt, Phys. Rev. C, 86:054601, (2012).

2. A. Al-Adili, F.-J. Hambsch, S. Pomp, S. Oberstedt, Nucl. Data. Sheets 119, 342 (2014).

3. K. Jansson, M.-O. Frégeau, A. Al-Adili, A. Göök, C. Gustavsson, F.-J. Hambsch, S. Oberstedt, S. Pomp, EPJ Web Conf., 146:04016, (2017).

4. A. Al-Adili, D. Tarrío, F.-J. Hambsch, A. Göök, K. Jansson, A. Solders, V. Rakapoulos, C. Gustavsson, M. Lantz, A. Mattera, S. Oberstedt, A.V. Prokofiev, E. A. Sundén, M. Vidali, M. 252 Fig.3. The mass yield for Cf(sf) plotted for the sample and Österlund, S. Pomp, EPJ Web of Conferences backing sides (blue and red) and their average (green). The 146, 04056 (2017). data are compared with Ref. [5]. 5. A. Göök, F.-J. Hambsch and M. Vidali, Phys. Rev. C 90, 064611 (2014). 63

Developing the VERDI spectrometer and the 2E-2v method for measurements of correlated fission properties

Kaj Jansson,1 Ali Al-Adili,1, ∗ Erik Andersson-Sundén,1 Stephan Pomp,1 Alf Göök,2 and Stephan Oberstedt2 1Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden 2European Commission, DG Joint Research Centre, Directorate G - Nuclear Safety and Security, Unit G.2 SN3S, 2440 Geel, Belgium

1. INTRODUCTION

The fission spectrometer VERDI is under development at the JRC-Geel and intended to utilise the double-energy double- velocity (2E-2v) methodology to generate correlated fission data. Effectively, the 2E-2v technique will provide average pre- as well as post-neutron emission masses and kinetic energies for both the light and heavy fragments. Thus, the average neutron multiplicity (ν¯), as a function of any other observed quantity, can be estimated from the obtained masses. The neutron multiplicity is an important quantity for un- derstanding fission dynamics since it is closely related to the distribution of excitation energy between the two nascent frag- ments. A better knowledge of the neutron multiplicity, as well Fig. 1. Schematic illustration of the VERDI setup (not to scale). as the precise mass yields from the 2E-2v method, help the development of fission models. Higher quality mass yields could also be of interest to the development of Gen-IV reactor distance is known the velocity can be calculated. The detected concepts. fragment must pass through both the acceleration grid as well However, since the neutron emission is never directly ob- as the electrostatic mirror in order to reach a silicon detector. served, all quantities and correlations can only be obtained as The total transmission ratio is estimated to be 85.7 %. average values due to the fragments recoil upon neutron emis- All measurements conducted with VERDI have been with 252 sions. That is, the quantities and correlations are not valid a Cf (sf ) source giving a fission rate of about 2 kHz. The 252 on an event-by-event basis, only when averaged over a larger calibration is planned to be based on Cf (sf ), but as the setup ensemble. and analysis procedure matures the mid section of VERDI First results from VERDI was published by Frégeau et al. will be replaced to facilitate a neutron beam, thus allowing [1], but since then both the experimental setup [2, 3] and independent studies of many different fissionable nuclei. the methodology [3] have been refined. Here, we will first present the experimental setup and the basic methodology and then highligth some of our newest findings. For more details, 3. 2E-2V ANALYSIS discussion and results, the reader is referred to Ref. [3]. In this section we briefly show how the masses and energies are derived from the measured energies and velocities. We 2. EXPERIMENTAL SETUP denoted masses with M, energies with E, velocities (speed) with 3. A central assumption for this method is that the velocity pre In the VERDI setup (depicted in Fig. 1), the kinetic energies before neutron emission 3 can be well approximated with post pre post of the fragments are measured in silicon detector pairs. A total 3 . It has been known for long that h3 i ≈ h3 i [4], but pre post of 16 pairs of detectors are positioned on a spherical surface 3 does generally not approximate 3 very well for a single 0.5 m centred on the target area. Each pair consists of two event, except when no neutrons were emitted. Nonetheless, pre post pre 450 mm2 PIPS detectors facing each other. will we use 3 ≈ 3 whenever 3 needs to be estimated. The target is kept at −3 kV while acceleration grids on each The measured energies as well as the measured ToFs need to side of the target are grounded. The acceleration grids will be corrected since they were obtained using silicon detectors. send electrons, sputtered by the fragments as they leave the The plasma effects upon heavy ions impinging into silicon target, towards electrostatic mirrors that redirects the elec- detectors give rise to both Pulse Height Defects (PHD) and trons onto MCP detectors. By measuring the time difference Plasma Delay Times (PDT). These effects are both energy between the MCP signal and the silicon detector signal, a time- and mass dependent and thus not always easy to correct for. of-flight (ToF) is obtained for the detected fragment. Since the The PHD is corrected by the procedure suggested by Schmitt et al. [5], but with parameters corrected by Müller et al. [6]. To correct for the PDT several methods have been tried with various results [3]. It is now clear that the previously applied ∗ Corresponding author: [email protected] method suggested by Velkovska and McGrath [7] was wrong 64 2 and another method should be used. post post Since E and 3 are directly measured the post-neutron 7 mass VERDI Gook et al. 6 Epost Mpost = , (1) γ − 1 5 is known, where γ is the Lorentz factor. The pre-neutron 4 masses are determined by observing the momentum conserva- 3

tion of the Fission Fragments (FFs): Yield / %

post 2 pre 32 M = Msum , (2) 1 post γ1 post 3 + 3 1 1 γ2 2

pre pre 0 where Msum = M1 + M2 and γ2/γ1 ≈ 1. 80 100 120 140 160 180 pre One can estimate Msum as the compound nucleus mass, M / amu which for VERDI at this stage is always the mass of 252Cf, but that will overestimate the pre-neutron masses. The difference Fig. 2. Pre-neutron mass distribution measured by VERDI compared in binding energy goes into the kinetic energy of the fragments to the distribution obtained by Göök et al. [9]. thus decreasing the mass of the full system. We can estimate the pre-neutron Total Kinetic Energy (TKE) classically by

pre MCf-252 post post Synthetic data TKE = 31 32 , (3) 4 2 2E2v (Synthetic)

2E2v (Experimental) and thereby estimate Msum better: 3 3post3post pre 1 2 Msum ≈ MCf-252 − TKE = MCf-252 1 − . (4) 2

2 ν * + pre pre Once M is known, E is given similarly, to Eq. 1:- 1 Epre = Mpre(γ − 1). (5) 0 The neutron multiplicity, ν, can be estimated using the mass −1 difference before and after neutron emission: 80 90 100 110 120 130 140 150 160 170 pre Mpre − Mpost M / amu ν = , (6) Mn Fig. 3. Calculated average neutron multiplicity based on synthetic and experimental data, respectively. where Mn is the neutron mass. In order to further study the methodology in a controlled environment, we have conducted simulations based on the GEF code [8]. The synthetic data obtained in this way has over- and undershoot, respectively, on each side of the mass been analysed in the same way as the experimental data, using symmetry are artefacts of the analysis procedure. Similarly, ν¯ Eqs. 1 to 6, but is not affected by either PHD or PDT. is under- and overestimated, respectively, in the wings of the mass distribution. The discrepancies were traced down to the assumption 4. RESULTS 3pre ≈ 3post. Due to the neutron emission every single event will have a mass uncertainty inherent to the 2E-2v method of Preliminary results are encouraging, e.g., the Mpre distribu- about 0.8 amu (for 252Cf). Since Mpre correlates with ν, the tion (Fig. 2) shows a higher peak-to-valley ratio compared to average quantity ν¯(Mpre) will be heavily affected where the the data from Göök et al. [9], which could be interpreted as mass yield changes a lot between neighbouring masses. This superior resolution. correlation effect seem to have escaped previous experimen- But here, we will focus on the obtained neutron multiplicity, talists, but as we demonstrate in Fig. 4, it is possible to correct especially as a function of Mpre. In Fig. 3 the experimentally for by deconvoluting the data after the main analysis. More obtained ν¯ is compared to the analysed synthetic data as well details of this inherent discrepancy and the correction proce- as the sawtooth shape obtained directly from GEF. We see dure is available in a separate upcoming publication (currently that the 2E-2v-analysed ν¯ share some common features no awaiting peer-review) [10]. matter if it originates from synthetic or experimental data. The The correlation problem is common to every 2E-2v exper- 65 3

small deviations from collinearity makes a difference. Frag- 4.5 ments with low TKE, emitting more neutrons on average, are Truth 7 4 2E-2v much less likely to be detected in coincidence than high TKE 2E-2v Corrected fragments. Fig. 5 shows that the coincidence probability is a 3.5 Mass yield 6 strong function of TKE. However, we have not yet observed 3 5 any major distortions of correlations or any other results due 2.5 4 to this.

ν 2 3

1.5 Mass yield / % 5. CONCLUSION AND OUTLOOK 2 1

1 0.5 The development of the VERDI setup is going forward.

0 0 The methodology had to be further developmed too, since a serious deficit in the treatment of the velocity approximation −0.5 80 90 100 110 120 130 140 150 160 170 and its implications on the correlations of fission observables pre M / amu was found. This teaches us to always apply the analysis to synthetic data, in order to sort out such problems from the Fig. 4. Corrected average neutron multiplicity based on synthetic beginning. data. The mass yield is shown as a reference. The previous handling of the PDT also turned out to be erroneous, and new methods had to be found. Before going further with the VERDI project the silicon detectors need to be properly characterised with respect to their timing properties. 1 The large dependence on TKE when detecting coincidences 0.9 between the two fragments is worrying, but we have not yet

0.8 found it to cause any major problems. Although, the situation will be worse with fast-neutron induced experiments when the 0.7 incoming neutron momentum breaks collinearity further. The 0.6 only remedy for this is to increase the detector solid angle 0.5 coverage without loosing timing performance.

0.4 Once we have a working PDT calibration for the silicon de- tector the setup should be fully operational. The next upgrade 0.3 will be a mid section made for receiving a neutron beam. To Coincidence probability 0.2 verify the calibration of VERDI based on 252Cf (sf ), the first 235 0.1 neutron-induced system to measure will be U(n,f). After

0 that, VERDI will be able to provide independent measure- 150 160 170 180 190 200 210 220 pre ments for almost any fissionable nucleus one can make a target TKE / MeV of. Fig. 5. The probability of detecting the other fragment given that one of the fragments is detected, as a function of TKEpre. ACKNOWLEDGMENTS

This work was supported by the European Commission iment. In addition to this, the silicon detectors add another within the Seventh Framework Programme through Fission- complication. Due to their small solid angle coverage, even 2013-CHANDA (project no.605203).

[1] M. Frégeau, S. Oberstedt, T. Gamboni, W. Geerts, F.-J. Hamb- Rev. C 29, 885 (1984). sch, and M. Vidali, Nucl. Instrum. Meth. A 817, 35 (2016). [7] J. Velkovska and R. McGrath, Nucl. Instrum. Meth. A 430, 507 [2] K. Jansson, M.-O. Frégeau, A. Al-Adili, A. Göök, C. Gustavs- (1999). son, F.-J. Hambsch, S. Oberstedt, and S. Pomp, EPJ Web Conf. [8] K.-H. Schmidt, B. Jurado, C. Amouroux, and C. Schmitt, Nucl. 146, 04016 (2017). Data Sheets 131, 107 (2016), special Issue on Nuclear Reaction [3] K. Jansson, Ph.D. thesis, Uppsala University (2017). Data. [4] W. E. Stein, Phys. Rev. 108, 94 (1957). [9] A. Göök, F.-J. Hambsch, and M. Vidali, Phys. Rev. C 90, 064611 [5] H. W. Schmitt, W. E. Kiker, and C. W. Williams, Phys. Rev. 137, (2014). B837 (1965). [10] K. Jansson, A. Al-Adili, E. Andersson Sundén, A. Göök, [6] R. Müller, A. A. Naqvi, F. Käppeler, and F. Dickmann, Phys. S. Oberstedt, and S. Pomp (2017), arXiv:1709.07443. 66

ELI-NP and EUFRAT – status of a collaboration

Andreas Oberstedt 1,*

1 Extreme Light Infrastructure - Nuclear Physics (ELI-NP) / Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN- HH), 077125 Bucharest-Magurele, Romania

1 ELI-NP an ionization chamber, also serving as beam monitor, which is carried out at JRC Geel [1]. So far, a 252Cf The Extreme Light Infrastructure – Nuclear Physics chamber was assembled for initial tests. A schematic (ELI-NP) is a project, for whose implementation the view and a photo of the test setup are displayed in Fig.1. Horia Hulubei National Institute for Physics and Nuclear The characterization of the chamber will also be Engineering (IFIN-HH) in Bucharest-Magurele, performed at JRC Geel within the EUFRAT programme, Romania, is responsible. ELI-NP is one of the three once MONNET has become operational. The aim of this pillars of the European Extreme Light Infrastructure presentation is to report on the status of on-going work (ELI) and a major European project for beyond state-of- involving both ELI-NP and JRC Geel, and to present an the-art research and education. It is one of the landmark overview of possible mutual research and experiments, facilities on the ESFRI (European Strategy Forum on for which EUFRAT is important. Research Infrastructures) list and co-financed by the European Commission and the Romanian Government pump flow-meter needle valve from Structural Funds via the European Regional exhaust Development Fund. 252 HV Cf CFD 2 The collaboration agreement trigger fan out

digitizer chamber preamp ionisation CAEN A1423 1 mm In April 2015 discussions between IFIN-HH and the

Joint Research Center (JRC) Geel (formerly known as CF4 PC IRMM) about a collaboration agreement were gas supply pressure flow-meter intensified, eventually leading to a Memorandum of controller Understanding (MoU) that was signed in February 2016. Through joint efforts of ELI-NP and the JRC, new approaches are to be identified and developed in the areas of nuclear science for nuclear safety, security, innovation of European research infrastructure, knowledge in sub-atomic physics, training and education, open access to research infrastructure and mobility of scientists thus working to the mutual benefit of both organizations in the achievement of their objectives.

3 Common activities Fig.1. Upper part: Schematic view of the experimental setup used for the tests. Lower part: Photo of the Cf-252 ionization Within two work programmes several actions were chamber with the cover removed (courtesy: A. Göök). defined, of which two have been submitted to be carried out in the framework of EUFRAT. The first one aims at neutron detector testing and characterization for gamma beam monitoring and experiments at ELI-NP, using the References neutron production facilities GELINA and MONNET at JRC Geel. Another action concerns the development of 1. A. Göök, private communication (2017).

* Corresponding author: [email protected] 67

Absolute and relative neutron-induced fission cross sections measurements of 235U, 238U, 237Np and 242Pu at NPL and JRC- Geel

P. Salvador-Castiñeira1, F.-J. Hambsch2*, A. Göök2, M. Vidali2, N.P. Hawkes1, N.J. Roberts1, G.C. Taylor1 and D.J. Thomas1

1 National Physical Laboratory, Hampton Road, Teddington, Middlesex, UK, TW11 0LW

2 EC-JRC-Geel, Retieseweg 111, B-2440 Geel, Belgium

Modelling of Generation-IV nuclear power plants requires high accurate values of several cross sections in the fast energy region. Cross section measurements are performed usually relative to the primary standard 235U(n,f), however in environments where the thermal and epi-thermal neutron background is non-negligible, other isotopes with a fission threshold should be preferred. Two of these isotopes are 238U(n,f) and 237Np(n,f). 238U(n,f) has a fission threshold at around En=1.6 MeV and is a secondary standard from En=2 MeV, nevertheless the JEFF 3.2 evaluation presents up to 7% discrepancies in the range of 1.5 MeV < En < 5 MeV with respect to the ENDF/B-VII.1. 237Np(n,f) would be more suitable as a standard because of its lower fission threshold (En=0.5 MeV) and its higher cross section above En=1.0 MeV, but some discrepancies have been found in recent measurements. To address these needs, two experimental campaigns have been performed under the CHANDA project at the Van de Graaff accelerator of the National Physical Laboratory (NPL, UK). The first campaign was performed in January 2016 and the isotopes measured were 235U(n,f), 238U(n,f) and 237Np(n,f). For the second campaign, performed in January 2017, we measured 235U(n,f), 237Np(n,f) and 242Pu(n,f). A twin Frisch-grid ionization chamber was used as fission fragment detector. In both cases measurements were done absolutely, by using a long counter to measure the neutron fluence, and relatively, by placing two samples in a back-to-back configuration in the fission chamber. Preliminary results are given in Fig. 1. To continue with Fig.1. Preliminary results from the campaigns at NPL for this extended study, a future experiment is planned at the 237Np(n,f) and 238U(n,f) at E from 0.57 MeV to 2.5 MeV. new MONNET (MONo-energetic NEutron Tower) n facility at JRC-Geel where high currents are available together with pulsed beams. References

1. C. Paradela, et al. (2010), Phys. Rev. C, 82(3), 034601

* Corresponding author: [email protected] 68

High-resolution measurements of the 12C cross sections for the (n,pn), (n,dn) exited states

M. Angelone1*, M. Pillon1, F. Belloni2, W. Geerts2, S. Loreti1, A.Milocco3, A.J.M. Plompen2

1 ENEA UT-FUS, C.R. Frascati, via E. Fermi 45, 00044 Frascati (Rome) Italy 2 European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, B - 2440 Geel, Belgium 3 CCFE, Culham Science Centre, Abingdon, OX14 3DB, UK

1 Introduction separated peaks were observed in the recorded PHS. The identified n-12C reactions, ordered in descending

Artificial diamond detectors are used to detect neutron peak energy, are : (n,α0); (n,p0); (n,p1); (n,d0); (n,p2); radiation thanks to their spectroscopic properties. (n,p3); (n,p4); (n,d1). For all of them the reaction cross Several nuclear reactions, already studied in several section was derived. It ought to be stressed that two of 12 12 12 12 papers [1-6], occur in carbon under neutron irradiation the reported cross sections ( C(n,p1) B, C(n,p4) B) producing several types of outgoing charged particles. were never measured before and this is an important The energy of these reaction products is released in the output of the present work. diamond detector producing an output signal proportional to the deposited energy. The output signal can be recorded as a pulse height spectrum (PHS) using 2 Experimental Set-up a multichannel analyzer (MCA) by performing the so- called Pulse Height Analyses (PHA). When only The used Single Crystal Diamond detector (SCD) was charged particles are produced in the exit channel of the fabricated by Istituto di Struttura della Materia (ISM), reaction and the available reaction energy (incident Consiglio Nazionale delle Ricerche (CNR), Rome, neutron energy plus Q-value) is deposited in the (Italy), while the electronics weas based upon standard detector volume, sharp peaks are observed in the PHS. CAEN company catalogue [9] components. ISM-CNR By contrast, wide distributions with characteristic edges produced the detector using an “electronic grade” (with are produced in the PHS when one or more neutrons are Nitrogen <5 ppb and Boron <1 ppb) Chemical Vapour present in the exit channels. The analysis of the Deposition (CVD) single crystal diamond (SCD) plate parameters of the sharp peaks in the PHS (net counts, (4.5x4.5mm2, thickness d=500 µm), bought from width, centroid position), after normalizing to the total Element Six Ltd [10]. ISM-CNR deposited square 200 neutron fluence and the number of carbon atoms in the nm thick multilayer gold finished contacts, 4.2x4.2mm2 detector, allow the evaluation of the reaction cross surface on both plate faces and then mounted the plate sections of each identified reaction channel in carbon. in an anodized aluminium casing using an alumina plate A paper was already published by some of the present 12 holder. A standard Sub Miniature version A (SMA) authors in which the cross sections of n+ C reaction connector is used to pick-up the signal output since this was measured using a diamond detector for both the connector results suitable for operating with fast signals ground and the excited levels of the produced reaction such as those produced by diamond. The detector active products [7]. This previous work was performed at the volume was calculated from an accurate measure of the Van de Graaff (VdG) neutron generator of EC-JRC- contacts area and diamond plate thickness. This it is IRMM [8] using a thick tritiated target which produces possible since it is has been experimentally mono-energetic neutrons with large energy demonstrated that the diamond sensitive region is distributions. This can led to the overlapping of the limited to the volume under the contacts [11]. From the observed peaks in the PHS. In order to improve the resulting active volume of 0.0088 cm3 and the density peaks separation and thus the analysis of the peaks of diamond (3.52(1) g cm-3) the number of 12C atoms themselves in the present work a very thin tritiated was derived. CAEN's electronics consisted of a single µ 2 target (263 g/cm ) was employed. Monoenergetic channel charge sensitive preamplifier, up to 200 pF neutrons in the energy range 18.91 MeV ÷ 20.69 MeV input capacitance, 45 mV/MeV (Si) sensitivity and a and with an intrinsic energy spread < 0.25% at FWHM DT5780, a Dual Digital Multi Channel Analyser were produced by bombarding the thin tritiated target (MCA) based on a 14-bits 100 MS/s flash ADC. with deuterons beams in the energy range 2.5 MeV – DT5780 directly accepts pulses from the charge 4.0 MeV. With such a narrow neutron energy spread, sensitive preamplifier performing a digital trapezoidal since the used diamond detector had an intrinsic energy shaping on exponential decaying signals. Complete resolution lower than 0.9% at FWHM, several well control of all the shaping parameters like trapezoid rise

* Corresponding author: [email protected] 69

time, flat top, etc. is possible. The diamond detector was operated with 600V negative bias during all the measurements. The use of the digitizer allowed to 2.2. Results record bi-dimensional PHS (time-amplitude). This allowed to remove some noise (for example produced by the VdG) so improving the peaks resolution and their Eight runs were performed with neutron energies separation. varying from 18.91MeV to 20.69 MeV. The gain of the electronics chain was set-up the same for all the runs. The neutron energies were calculated from the deuteron 2.1. Measurements beam energy using the D(t,n)4He relativistic kinematics. A typical PHS recorded with the measurement set-up The diamond detector was positioned at a distance of described above is shown in Figure 2. The energies of 54.45 mm from the VdG neutron target, at 0° with the peaks were obtained using the reaction Q-values as respect to the deuteron beam axis. A sandwich of two described in [13]. The measured peak energies-PHS activation foils, Al+Zr, was used as neutron fluence channel correlation (energy calibration) for almost all monitor. The foils were at the same distance of the SCD the investigated neutron energies resulted in a very but at an angle of 30°. At half of the distance between good linear correlation between peak positions versus the SCD and the target an aluminium disc, 1 mm thick, the deposited energy from the various reactions. A was positioned with the scope to shield the diamond small standard deviation was obtained indicating the detector from the energetic protons arising from the high quality determination of the impinging neutron D(3He,4He)p reaction. This reaction occurs in tritiated energies. targets due to the decay of tritium and the produced protons have an energy > 14 MeV and can produce a strong noise signal in open window SCD. An aluminium disc identical to the one used for the detector was positioned in front of the sandwich formed by the activation foils in order to compensate for the small neutron flux reduction caused by this aluminium shield. The set-up of foils and SCD detectors is shown in Fig. 1.

Fig. 2. Typical pulse height spectrum (PHS). The identified peaks produced by the investigated reactions are indicated.

The identified peaks in each PHS were fitted using the peak analysis software GAMMAVISIONTM 8.0 produced by ORTEC company and utilizing the analysis engine NAI32, designed specifically for some tens of keV resolution spectrum analysis. The statistical uncertainty in the reaction cross sections values (one standard deviation) was calculated as the quadrature sum of the peak analyses uncertainties and the fluence uncertainties. A maximum systematic uncertainty of ±5% can be attributed to the determination of 12C Fig.1. Experimental set-up showing the location of the number of atoms. Half of this contribution has been activation foils and of the SCD detector in front the VdG added in quadrature sum to compute the total tritiated target uncertainty. From the fitting procedure the energy of the peak, the peak width and its net area were obtained. The neutron induced reaction cross sections were derived as After each run the activation foils were counted with described in ref. [14]. All the measured cross section two absolutely calibrated HPGe detectors and the values with the associated uncertainties are reported in neutron fluence at the diamond detector position Tables 1 to 8. For some reactions the present derived. The methodology used is described in ref. 12. experimental data are also plotted and compared to the The uncertainty estimate for the fluence measurements existing data in the EXFOR database [15] or with the was ±2.5 % at one standard deviation. TENDL compilations available on the website [16]. The complete set of experimental data and their detailed 70

20.19 5.93 5.75E-03 2.6E-04 Eneut Edep Cross section Std. Dev. error 20.49 6.23 4.71E-03 2.2E-04 (MeV) (MeV) (barn) (barn) 20.69 6.43 5.64E-03 4.9E-04 18.91 3.70 3.32E-03 1.5E-04 19.24 4.03 2.59E-03 1.7E-04 Table 5. 12C(n,p )12B measured cross section values. 19.54 4.33 2.89E-03 3.5E-04 3 19.56 4.35 2.84E-03 1.3E-04 12 12 19.88 4.67 3.03E-03 1.6E-04 Table 6. C(n,p4) B measured cross section values. 20.19 4.98 3.60E-03 1.6E-04 20.49 5.28 2.89E-03 1.4E-04 Eneut Edep Cross section Std. Dev. error (MeV) (MeV) (barn) (barn) 20.69 5.48 3.15E-03 2.9E-04 18.91 3.60 1.36E-03 9.7E-05 comparison with the EXFORD data or theoretical predictions from TENDL is reported in [17]. 19.24 3.93 2.12E-03 1.7E-04 19.54 4.23 1.29E-03 2.9E-04 12 9 Table 1. C(n,α0) Be measured cross section values. 19.56 4.25 1.31E-03 1.0E-04 19.88 4.57 1.46E-03 1.2E-04 Eneut Edep Cross section Std. Dev. error 20.19 4.88 1.58E-03 1.1E-04 (MeV) (MeV) (barn) (barn) 20.49 5.18 1.19E-03 1.1E-04 18.91 13.21 2.20E-02 8E-04 20.69 5.38 1.16E-03 2.4E-04 19.24 13.54 1.75E-02 6E-04 19.54 13.84 2.53E-02 1.3E-03 12 11 19.56 13.86 2.58E-02 9E-04 Table 7. C(n,d0) B measured cross section values.

19.88 14.18 3.69E-02 1.3E-03 Eneut Edep Cross section Std. Dev. error 20.19 14.49 3.42E-02 1.2E-03 (MeV) (MeV) (barn) (barn) 20.49 14.79 2.97E-02 1.1E-03 18.91 5.18 5.97E-02 2.1E-03 20.69 14.99 3.11E-02 1.6E-03 19.24 5.51 4.40E-02 1.6E-03 19.54 5.81 3.74E-02 2.2E-03 12 12 19.56 5.83 4.08E-02 1.5E-03 Table 2. C(n,p0) B measured cross section values. 19.88 6.15 4.73E-02 1.7E-03 Eneut Edep Cross section Std. Dev. 20.19 6.46 4.28E-02 1.5E-03 (MeV) (MeV) (barn) error (barn) 20.49 6.76 3.94E-02 1.4E-03 18.91 6.32 1.13E-02 4E-04 20.69 6.96 4.62E-02 2.7E-03 19.24 6.65 9.80E-03 4.0E-04 19.54 6.95 1.13E-02 8E-04 19.56 6.97 1.03E-02 4E-04 19.88 7.29 1.15E-02 4E-04 3 Data Analysis and Discussion 20.19 7.60 9.62E-03 3.9E-04 A discussion about the reported data is necessary and it 20.49 7.90 7.62E-03 3.2E-04 is addressed here after for some of the measured cross 20.69 8.10 8.62E-03 6.3E-04 sections. First of all let stress that caution would be required in 12 12 Table 3. C(n,p1) B measured cross-section values. the comparison of our measurements with the TENDL data. This library is produced by the evaluation code E E Cross section Std. Dev. error neut dep TALYS [18] which relies on physics models that are (MeV) (MeV) (barn) (barn) statistical in nature. Hence, with small number of 18.91 5.37 1.38E-02 5E-04 nucleons (12 in the case of Carbon) these models might 19.24 5.70 6.87E-03 2.9E-04 be inappropriate and the partial cross sections might be 19.54 6.00 8.21E-03 5.5E-04 questionable. 19.56 6.02 8.69E-03 3.2E-04 As an example, the data of Table-1 are plotted in Fig. 3 19.88 6.34 1.39E-02 5E-04 for comparison with EAF and EXFOR data base. A 20.19 6.65 1.16E-02 4E-04 good agreement is found between our new experimental 20.49 6.95 1.09E-02 4E-04 12 9 data of C(n,α0) Be reaction cross section with the 20.69 7.15 1.20E-02 8E-04 experimental data from Stevens in EXFOR (see insert). 12 12 Table 4. C(n,p2) B measured cross section values. 12 11 Table 8. C(n,d1) B measured cross-section values. Eneut Edep Cross section Std. Dev. error (MeV) (MeV) (barn) (barn) Eneut Edep Cross section Std. Dev. error 18.91 4.65 5.83E-03 2.4E-04 (MeV) (MeV) (barn) (barn) 19.24 4.98 2.89E-03 1.9E-04 18.91 3.05 4.18E-03 1.9E-04 19.54 5.28 4.17E-03 4.9E-04 19.24 3.38 5.06E-03 2.4E-04 19.56 5.30 3.89E-03 1.8E-04 19.54 3.68 6.68E-03 6.4E-04 19.88 5.62 6.14E-03 2.8E-04 19.56 3.70 6.22E-03 2.4E-04 71

19.88 4.02 7.32E-03 2.9E-04 20.19 4.33 7.20E-03 2.8E-04 20.49 4.63 6.70E-03 2.7E-04 20.69 4.83 5.92E-03 4.9E-04

12 12 Fig. 5. C(n,p4) B results compared with TENDL compilations.

In this case only TENDL-2009 compilation mimic the 12 12 12 9 experimental data. It is stressed that the C(n,p4) B Fig. 3. C(n,α0) Be results compared with EAF 2010 and available experimental data in EXFOR database. cross sections are new data, never measured before.

4 Conclusions As further example, the data of Table-2 for the 12 12 C(n,p0) B reaction are plotted in Fig. 4. In this case the comparison with TENDL evaluation is also shown. Several partial cross sections to discrete levels of fast Only TENDL-2009 compilation reproduces our new neutron interaction with 12C have been measured using experimental data which are higher than previous a diamond detector. Two of these cross sections 12 12 12 12 published data in 2011. The reason for that is under ( C(n,p1) B and C(n,p4) B respectively) were investigation. measured for the first time in this work.

The experimental cross sections compared to different evaluations from TENDL compilation show a not uniform scenario. In most of the cases TENDL 2009 results to be the best compilation, however in the case 12 11 of C(n,d1) B reaction the latest compilation of TENDL 2015 produces better results than TENDL 2009.

The results of this work extend or further support previous finding and can be useful for the improvement of the knowledge of mechanism of the neutron carbon interaction as well as the validation of nuclear models 12 used for predicting the C(n,pn or dn) reactions. 12 12 Fig. 4. C(n,p0) B results compared with TENDL compilations. Acknowledgments

As final example of comparison with TENDL data, the This work was supported by the European Commission within experimental cross sections of Table-6 for the the FP7 EUFRAT program. The authors thank the operators of 12 12 C(n,p4) B reaction are shown in fig. 5. the IRMM VdG accelerator for the providing the conditions necessary for these experiments.

References

1. Dmitrievich Kovalchuk, V., Igorevich Trotsik, V., (1994) Nuclear Inst. and Methods in Physics Research, A, 351 (2-3), pp. 590-591. 72

2. Pillon, M., Angelone, M., Krasilnikov, A.V. (1995) Nuclear Inst. and Methods in Physics Research, B, 101 (4), pp. 473-483. 3. Pillon, M., Angelone, M., Krása, A., Plompen, A.J.M., Schillebeeckx, P., Sergi, M.L. (2011) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 640 (1), pp. 185-191. 4. Milocco, A., Pillon, M., Angelone, M., Plompen, A., Krása, A., Trkov, A. (2013) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 720, pp. 74-77. 5. Zbǒril, M., Araque, J.E.G., Nolte, R., Zimbal, A. Proceedings of Science, Volume 2015-January, 2015, 1st EPS Conference on Plasma Diagnostics, ECPD 2015; Frascati; Italy; 14-17 April 2015 Code 118792 6. Osipenko, M., Ripani, M., Ricco, G., Caiffi, B., Pompili, F., Pillon, M., Verona-Rinati, G., Cardarelli, R. (2016) Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 817, pp. 19-25. 7. Pillon, M., Angelone, M., Krása, A., Plompen, A.J.M., Schillebeeckx, P., Sergi, M.L. (2011) AIP Conference Proceedings, 1412, pp. 121-128. 8. C. Sage, V. Semkova, O. Bouland, P. Dessagne, A. Fernandez, F. Gunsing, C. Nästren, G. Noguère, H. Ottmar, A.J.M. Plompen, P. Romain, G. Rudolf, J. Somers, F. Wastin, Phys. Rev. C 81, 064604 (2010) 9. CAEN S.p.A., see http//www.caen.it/. 10. Element Six Ltd., see http://www.e6cvd.com/. 11. C. Verona, G. Magrin, P. Solevi, V. Grilj, M. Jaksic, R. Mayer, Marco Marinelli and G. Verona- Rinati, Journal of Applied Physics 118, 184503 (2015) 12. S. Jakhar, C. V. S. Rao, A. Shyam and B. Das, "Measurement of 14 MeV neutron flux from D-T neutron generator using activation analysis," 2008 IEEE Nuclear Science Symposium Conference Record, Dresden, Germany, 2008, pp. 2335-2338. 13. Paić, G., Kadija, K., Ilijaš, B., Kovačević, K., Nucl. Instrum. Meth. 188 (1981) 119 14. H.J. Brede, G. Dietze, H. Klein and H. Schölermann, Nucl. Sci. Eng. 107 (1991) 22 – 347 15. EXFOR: Experimental Nuclear Reaction Data - http://www-nds.iaea.org/exfor/ 16. TALYS-based evaluated nuclear data library: http://www.talys.eu/home/ 17. M. Pillon, M. Angelone, F. Belloni, W. Geerts, S. loreti, A. Milocco, A.J.M. Plompen, “High- resolution measurements of the exited states (n,pn), (n,dn) C-12 cross sections”, Proc. of the ND-2016 Conference (Bruges), EPJ Web of Conferences 146, 11005 (2017) 18. A.J. Koning and D. Rochman, "Modern Nuclear Data Evaluation With The TALYS Code System", Nuclear Data Sheets 113 (2012) 2841

73

Diamond detector measurements at VdG/MONNET and GELINA

Christina Weiss*,1, Erich Griesmayer1, Pavel Kavrigin1, Arjan Plompen2, Peter Schillebeeckx2, Jan Heyse2 and Francesca Belloni2

1 CIVIDEC Instrumentation GmbH and TU Wien, Austria

2 EC-JRC, Geel/Belgium

1 Introduction A CIVIDEC Cx Spectroscopic Shaping Amplifier and a CIVIDEC C2 Broadband Amplifier, 2 GHz, 40 dB were Two measurement campaigns at EC-JRC Geel/Belgium used during the measurement campaign. were performed with single-crystal Chemical Vapour As data acquisition system (DAQ) a 2 GHz LeCroy Deposition (sCVD) diamond detectors: digital oscilloscope and the CIVIDEC ROSY® AX106 The first measurement was performed at the Van de were used simultaneously, where the acquired raw Graaff accelerator and was focusing on the usage of signals were recorded and analyzed offline. This lead to sCVD diamond detectors for fast neutron monitoring in a dead-time in both DAQ systems which prevented mono-energetic neutron beams. The diamond sensor making absolute cross-section measurements. itself, namely the Carbon isotopes 12C and 13C of the diamond sensor, are used in such measurements as 2.2. Analysis technique neutron converters. The results of the measurement, which is reported on in Chapter 2, are published in With the measurements using the CIVIDEC C2 References [1 - 3]. Broadband Amplifier the detector current signals in fast The second measurement was performed at GELINA neutron fields were investigated. A novel analysis and was focusing on the usage of diamond detectors in 235 technique was developed which distinguishes the combination with a U neutron converter. The aim was recorded signals by origin and allows the rejection of to make first test measurements with a sCVD diamond background. based detector with exchangeable neutron converter for The detector response functions were analyzed using this applications in spent-fuel ponds. The results of the novel technique, where background originating from measurement are discussed in Chapter 3. proton recoils from the PCB structure surrounding the diamond sensor was rejected. The resulting response function allowed measuring the cross-section of 2 Fast-neutron detection with sCVD 13 10 C(n,α0) Be, as described below. diamond detectors The technique is based on pulse-shape analysis of the detector current signals and it is published in full detail 2.1. Experimental setup in Reference [2]. Further applications of this technique are reported on in Reference [3]. The response function of 500 µm and 150 µm sCVD diamond sensors was measured at the Van de Graaff accelerator, with a 2 MeV deuteron beam impinging on a 2.3. Response function at 14.3 and 17 MeV triton target. Different angles with respect to the neutron energy incoming d-beam were used for measurements at The response functions at 14.3 MeV and 17 MeV 14.3 MeV, 17 MeV and 18 MeV neutron energy. neutron energy were analysed in full detail and the The diamond sensors were mounted in a RF-tight printed 13 10 C(n,α0) Be cross-section extracted. The resulting circuit board (PCB) structure to prevent any disturbance spectra were compared to GEANT4 simulations of the of the measurement by noise induced by electromagnetic experimental setup. Figure 1 shows the measured interference (EMI) and allow the measurement of the response function at 14.3 MeV neutron energy. detector current signals in the GHz range.

* Corresponding author: [email protected] 74

Fig. 2: Schematics of the detector geometry.

of-flight (TOF) applications at GELINA was used for this experiment. Fig. 1 Response function of sCVD diamond detectors to 14.3 MeV neutrons. 3.2. Results Due to the dead-time of the DAQ-systems an absolute measurement of the cross-section was not possible. The The recorded spectrum of fission fragments is shown in 13 10 C(n,α0) Be cross-section was evaluated relative to Figure 3. The spectrum shows a good separation 12 9 235 C(n,α0) Be. The following absolute values were between the α-particles from the natural decay of U published in Reference [1] based on the CENDL-3.1. and the fission fragments. evaluated nuclear data library:

10.4 1.1 mb at 14.3 MeV 7.1 0.7 mb at 17 MeV

3 Neutron detection with 235U and sCVD diamond detectors for spent-fuel applications

The goal of the experiment was to demonstrate the performance of a sCVD diamond detector using a 235U layer for the neutron conversion. Such radiation hard detectors, which are resistant against gamma-rays, are a promising new candidate for industrial applications in Fig 3: Recorded spectrum of the deposited energy in the sCVD the field of nuclear safeguards and security, e.g. they can diamond detector. be used for the verification of spent fuel assemblies in a 235 fuel storage pond and for SINRD (self-interrogation The spectrum is calibrated to the α-particles from U. neutron resonance densitometry) measurements in dry The spectrum of the fission fragments is shifted to lower storage areas requiring a detector that has a high energies with respect to the expectations, due to the air sensitivity to resonance of fissile material such as 235U, gap, the electrode and the high ionization density in the 239Pu and 241Pu. diamond sensor, caused by the heavy fission fragments. Such detectors can be constructed in compact Additional measurements and further developments are geometries, similar to small fission chambers, and allow planned to optimize the sCVD diamond detector setup the installation inside small rods with inner perimeters of for spent-fuel applications. few millimeters. In addition they allow the exchange of the converter material according to the respective application. References

3.1. Experimental setup 1. P. Kavrigin, E. Griesmayer, F. Belloni, A.J.M. Plompen, P. Schillebeeckx, and C. Weiss, Eur. A 500 µm thick sCVD diamond sensor with 2.5 mm Phys. J. A 52: 179 (2016). diameter active area was used for the measurement. The 2. C. Weiss, H. Frais-Kölbl, E. Griesmayer and P. 235U layer with 270 µg/cm2, which was produced at EC- Kavrigin, Eur. Phys. J. A 52: 269 (2016). JRC by electro-deposition, was mounted in close 3. C. Weiss, H. Frais-Kölbl, E. Griesmayer and P. geometry to the diamond sensor on a removable PCB Kavrigin, EPJ Web of Conferences 146, 03004 plate, as shown in Figure 2. The detector was operated in (2017). air. A CAEN amplifier with a timing and charge integration output was used, where the slow output was additionally shaped. The standard data acquisition system for time- 75

Assessment of the EJ-200 plastic scintillator as an active background shield for neutron detection systems

A.H. Tkaczyk1*, H. Saare1, C. Ipbüker1, F. Schulte2, P. Mastinu3, J. Paepen4, B. Pedersen5, P. Schillebeeckx4, G. Varasano5

1 University of Tartu, Institute of Physics, W. Ostwaldi 1, EE – 50411 Tartu, Estonia

2 Fachhochschule Aachen, University of Applied Sciences, D - 52005 Aachen, Germany

3 INFN, Laboratori Nazionali di Legnaro, I – 35020 Legnaro, Italy

4 European Commission, Joint Research Centre, B – 2440 Geel, Belgium

5 European Commission, Joint Research Centre, I – 21027 Ispra, Italy

1 Introduction 2 Methodology Neutron detection is commonly used for the The performance of six rectangular EJ-200 plastic characterization of nuclear waste by passive non- scintillators, composed of polyvinyltoluene polymer with destructive analysis (NDA) methods [1-3]. Passive NDA different thicknesses (12.7 mm, 20 mm, and 25 mm) and waste characterization systems often consist of an array coupled to a photomultiplier tube was investigated. Two of detectors, sensitive to low-energy neutrons, that are signals were provided: one from the anode and another embedded in a neutron moderator [1-3]. The detected from the last dynode. A light guide made out signal pulse train representing the time of detection of polymethylmethacrylate was used to match the neutrons allows for the so-called multiplicity analysis of rectangular shape of the scintillator with a cylindrical correlated neutrons. A significant part of the neutron PMT. background in such systems is caused by atmospheric muons [4]. Muons of several GeV are produced in the To obtain response functions for the detection of gamma atmosphere from reactions of high energy cosmic rays, four radionuclide sources (137Cs, 232Th, 238PuC, particles. Muons interacting with material of high atomic 241AmBe) were used. Response functions for neutrons number can produce multiple neutrons in a spallation were obtained from experiments with quasi mono- event. This part of the neutron background is particularly energetic neutrons at the Van de Graaff accelerator of disturbing the neutron correlation analysis by which the JRC Geel, Belgium and from time-of-flight spontaneous fission rate and the spontaneous fissile mass measurements at the Van de Graaff accelerator of the can be determined [5]. INFN in Legnaro, Italy. Experimental response functions for muons were determined from ambient background Passive shielding has proven to be ineffective against measurements carried out at JRC Geel, with scintillation this part of the neutron background as the additional detectors in vertical and horizontal positions. amount of material near the detector would increase the background caused by cosmic rays. To reduce the background created by muon induced events, an active 3 Results and Discussion shield consisting of plastic scintillation detectors placed around the waste assay system can be used. When 3.1. Response functions for gamma rays scintillation detectors detect a muon, the signal processing in the neutron detection system is vetoed for a The experimental response functions for the 25 mm thick fixed amount of time to disregard the spallation neutrons EJ-200 detector using the 137Cs, 232Th, and 238PuC that may have been produced by the muon. For such an radionuclide sources were obtained. They were derived active shield, plastic scintillation detectors are a viable from the dynode signal and fitted in a region around the option, as they have relatively low cost, they are non- Compton edge using a theoretical distribution obtained toxic, non-flammable and can be shaped and fabricated from MCNP simulations. A good agreement between with ease [6]. experimental and theoretical response functions was In this work, the use of commercially available plastic achieved, although around the Compton edge the scintillation detectors to act as an active shield in a low- theoretical response in the low energy region is lower level nuclear waste detection system is investigated. EJ- than the experimental one. This is mainly due to the 200 scintillators of different thicknesses were limitations of the theoretical response, which was characterized for their response to gamma-rays, neutrons, simulated only for the highest energy gamma ray of the and muons. source.

The light output for electrons derived from both the dynode and anode signal displays a non-linearity as a

* Corresponding author: [email protected] 76

function of electron energy. Schölermann and Klein [7] The obtained spectra also reveal that for the 20 mm and noticed that a strong non-linear dependency for electrons 25 mm thick detector the contribution due to muon is mostly related to the PMT performance and non-ideal background can be separated from the natural gamma ray light collection due to the quality of the coupling background by applying an energy threshold of 3.1 MeV between the PMT and scintillator. For detection systems and 3.7 MeV, respectively, on the observed light output. that are optimised for gamma ray or neutron For the 12.7 mm thick detector a threshold of about spectroscopic measurements, a linear behaviour is 2.2 MeV would result in more than 20% false expected. The scintillators used in this study however are identification of muons. Hence, a plastic scintillator with not optimised for such studies but for the role of an a minimum thickness of 20 mm is necessary to separate active shield, which has an impact on the quality of the the events due to muon detection from the events caused light collection. by the detection of neutron produced by nuclear waste and natural gamma ray background. 3.2. Response functions for neutrons The veto signal can even be improved by using a stack of Experimental and theoretical response functions for two plastic scintillators on top of each other and neutrons with an energy of 4.5 MeV and 19 MeV were considering in addition to the light output discrimination obtained. In the region of maximum energy transfer the also coincident events, where a veto signal is created experimental data derived from the dynode signal can be only if both detectors produce a signal within a short reproduced using a non-linear light output function. The time frame. To investigate the effectiveness of such a agreement is not as good when a direct proportionality system, background measurements were carried out with between light output and proton energy is assumed. It the 20 mm thick scintillator placed on top of the 25 mm can be concluded that the data needs to be described with detector. The total contribution of events in the 25 mm a non-linear light output function. detector with L > 3.7 MeV is reduced by only 8% and 15% by imposing a coincidence condition with events in The specific light output and relative resolution were the 20 mm detector and applying in addition a threshold also obtained from these data. In a comparison of the at L(20 mm) > 3.1 MeV, respectively. However the specific light output for electrons and protons for the contribution due to natural gamma ray background is 25 mm thick scintillator, the light output for protons is substantially reduced by more than 90% and 99%, significantly reduced compared to the one for electrons. respectively. The relative resolution as a function of light output for the 25 mm thick EJ-200 scintillator is also obtained from the dynode signal, and compared for protons and 4 Conclusion electrons. The obtained results confirm that resolution as a function of light output is not strongly dependent on The main objective of this paper was to demonstrate the the charged particle type as also noted in [8]. feasibility to use EJ-200 plastic scintillators as veto detector to reduce the impact of muon background for 3.3. Response for muons waste characterization measurements based on the detection of neutrons. The light output function, i.e. the amount of light as a function of charged particle energy, The response for a 20 mm thick scintillator placed for electrons showed a non-linear behaviour, even in the horizontally and vertically is compared. It is observed low-energy region. This is most likely due to a non-ideal that the structures around L ≈ 1.2 MeV and L ≈ 2.3 MeV light collection. The light output function for protons for are associated with the Compton edges resulting from the energies below 20 MeV is strongly non-linear and detection of gamma rays emitted in the decay of 40K and several times smaller compared to the one for electrons. 208Tl, respectively. Except for the thinnest detector where The type of the charged particle producing the light does the muon peak obscures the edge at 2.3 MeV, these not affect the resolution as function of light output. structures are also visible in the spectra taken with the Results of measurements in background conditions 12.7 mm and 25 mm thick scintillators. In the suggest that the light output function for muons can be measurements done with the horizontally oriented approximated by the light output for electrons. Signals 20 mm thick detector, a broad peak around light outputs resulting from the detection of gamma rays or neutrons L ≈ 4.4 MeV is observed. This peak is caused by the can be separated from signals due to atmospheric muons muons passing through the detector with a path length by a simple discrimination on the light output. For such a corresponding to the thickness of the detector. For the separation a scintillator with a minimum thickness of plastic scintillators studied in this work their energy loss 20 mm is required. A signal indicating the detection of a is about dE/dx ≈ 2 MeV/cm. Such an energy loss is muon can also be created by selecting only coincident consistent the observed peak at L ≈ 4.4 MeV in the events between two detectors. 20 mm thick scintillator. The good agreement between the simulated and experimental response around the peak also suggests that the light output and resolution function for muons is close to those for electrons.

77

Acknowledgement

The experiments at the Van de Graaff accelerator of JRC Geel (Belgium) were supported by the 327-ARI-ET project (EUFRAT) of the JRC. We are grateful to the technical staff of the CN accelerator of the INFN Legnaro (Italy) and the Van de Graaff accelerator of the JRC Geel. F. Schulte acknowledges the financial support of the EURATOM Fission 7th Framework Programme's project GENTLE (grant number 323304) for the experiments at the Van de Graaff facility of JRC Geel.

References

1. W. Hage, Nondestructive fissile material assay by induced fission neutron correlation, Nuclear Instruments and Methods in Physics Research Section A, 551 (2005) 396-419. 2. B. Pedersen, W. Hage, A. Favalli and G. Varasano, Assay of small fissile masses in waste by the active neutron correlation technique, Proc. of Symposium on International Safeguards: Addressing Verification Challenges, IAEA, October 2006, Vienna, Austria. 3. B. Pedersen, application of the Passive Neutron Correlation Technique to the Assay of Pu in radioactive Waste, Ph.D. Thesis, Reactor Centre, Imperial College of Science, Technology & Medicine, University of London, 1993. 4. J. Beringer et al. (Particle Data Group), Review of Particle Physics, Physical Review D 86 (2012) 010001. 5. M. G. Paff, B. Pedersen, J.-M. Crochemore, V. Mayorov, M. Mosconi, E. Roesgen, E. Pirovano, V. Canadell Bofarull, Characterization of the Cosmic Ray Induced Neutron Multiplicity Background of a He-3 Passive Drum Counter for Plutonium Waste Verification, Proceedings of the Institute of Nuclear Materials Management 54th Annual Meeting in Palm Desert, CA, July 2013. 6. G. Knoll, Radiation Detection and Measurement, Michigan, John Wiley & Sons, 1989. 7. H. Schölermann, H. Klein, Optimizing the energy resolution of scintillation counters at high energies, Nuclear Instruments and Methods in Physics Research Section A, 169 (1980) 25 - 32. 8. G. Wright, Scintillation Response of Organic Phosphors, Physical Review, 91 (1953) 1282. 78

Fabrication of thin actinide layers for applications in nuclear chemistry and -physics

Klaus Eberhardt1,*, C.E. Düllmann1,2,3, C. Mokry1, J. Runke3, P. Thörle-Pospiech1 and N. Trautmann2

1Johannes Gutenberg-Universität Mainz, 55099 Mainz Germany; 2Helmholtz-Institut Mainz, Johannes Gutenberg-Universität Mainz , 55099 Mainz, Germany; 3GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany;

1. Introduction used or destroyed targets. Here, ion chromatographic separation techniques are frequently applied. For yield Thin actinide layers deposited on metallic or non- determination α-particle spectroscopy, γ-spectroscopy metallic substrates are widely used as calibration sources and Neutron Activation Analysis is routinely used. Layer in nuclear spectroscopy. Other applications include homogeneity is checked with Radiographic Imaging (RI) fundamental research in nuclear chemistry and –physics, [11-13]. As an alternative technique to MP the e.g. the chemical and physical properties of super-heavy production of thin lanthanide and actinide layers by the elements (SHE, Z > 103) or nuclear reaction studies with so-called “Drop-on-Demand”-technique that is also heavy ions [1,2]. Here, layers of actinide target nuclei applied in ink-jet printers is currently investigated [14]. such as 238U, 242/244Pu, 248Cm, 249Bk, and 249Cf, 2 respectively, with areal mass densities up to 1 mg/cm 3. Examples deposited on 1-2 µm thin metallic foils are required. For the design of future nuclear reactors like fast-fission 3.1. Chemical purification of plutonium reactors and accelerator-driven systems for To prepare 242Pu targets for neutron absorption cross transmutation of nuclear waste, precise data for neutron section measurements at the n_TOF facility at CERN [4] absorption as well as neutron-induced fission cross 242 242 about 220 mg of Pu oxide material, enriched in Pu was section data for Pu with neutrons of different energies used (Oak Ridge National Laboratory, Oak Ridge, are of particular importance [3-5]. A recent application 229 USA). Its isotopic composition (wt %) was 0.003% include studies of nuclear transitions in Th [6]. For 238 239 240 241 233 Pu, 0.005 % Pu, 0.022 % Pu, 0.009 % Pu, this, a thin and very smooth layer of U is used [7]. 99.959 % 242Pu, and 0.002 % 244Pu (assay date: February 28, 1980). In a Teflon beaker the Pu-oxide was dissolved 2. Fabrication of thin actinide layers using 15 mL of 65% HNO3 and 5 mL of 48% HF while carefully stirring and heating to 80°C with a hot plate For the preparation of thin actinide layers - where the and an infrared (IR) lamp. Complete dissolution took desired target material is available only in limited about three days. In solution, fluoride ions are known to amounts or highly radioactive - Electrochemical form strong complexes with Pu and thus hinder Deposition (ED) techniques are widely used. Advantages deposition. To prevent this, the fluoride ions were of these methods are their simplicity and high deposition removed as BF by adding 4.4 M H BO solution and yields as well as the capability of producing a wide range 3 3 3 heating the solution to 80°C. Then Pu was precipitated as in target thicknesses. A special form of ED is called hydroxide by adding 25% NH3 until a pH = 9 was Molecular Plating (MP). For MP the compound to be reached. The resulting precipitate was filtered, washed deposited, typically the nitrate, is dissolved in a small with warm NH3-solution, and subsequently dissolved in volume (5-20 µL) of 0.1 N nitric acid and the aqueous 8 M HCl. A complete recovery of Pu was obtained after phase is then mixed with a surplus of an organic solvent. a second precipitation step from the washing solution Suitable solvents are e.g. isopropanol and isobutanol. [13]. Deposition is performed by applying electric current 241 2 The Pu (t1/2 = 14.3 a) that was originally present in the densities in the mA/cm range at voltages up to 1500 V base material had substantially decayed into 241Am, [8-10]. Under these conditions, layers with areal 2 which was separated from the Pu by anion exchange densities up to 1 mg/cm can be produced in a single chromatography prior to deposition. For this, an aliquot deposition step. Very often chemical separation 242 of 25 mL containing 129 mg Pu of the Pu stock procedures are required prior to deposition to ensure solution was used. The 25 mL volume was divided into 4 high purity of the deposited target material, to recover batches (about 6.2 mL each) which were separately the material in the case that deposition failed or from purified. Prior to separation few drops of 65% HNO3

* Corresponding author: [email protected] 79

were added. This solution was then fed onto a The homogeneity of the produced 242Pu-deposit was preconditioned anion exchange column (Dowex AG investigated by RI [11]. A commercial RI system 241 1X8) kept at a temperature of 55 °C. The Am was (FUJIFILM FLA 7000) equipped with reusable imaging washed from the column with 4 x 5 mL 8 M HCl. Pu plates sensitive to α-particles was used to record the was subsequently eluted with a total of 25 mL of 0.5 M distribution of the Pu activity. Figure 2 shows HNO3. α-particle spectroscopy was used to confirm the 241 radiographic images of three targets. One can see that the complete removal of Am and to evaluate the activity is homogeneously distributed over the entire ≥ separation yield for Pu. A Pu-recovery of 85 % was target area. The deposit is well confined within a circular determined [13]. spot of 45 mm diameter. 3.2. Preparation of 242Pu- targets The general design of the plating cell used for MP of large-area targets is described in a previous publication (see [13] for details). For plating of plutonium Kel-F™ was used as cell material. The cell consists of a central Kel-F™ body where the electrolytic solution has to be inserted. Deposition was performed onto a 10 µm thick Fig. 2. Radiographic images of 242Pu targets produced by MP Al foil covered with 50 nm of Ti and glued onto a ring- (see text for details). The 242Pu areal densities (in [µg/cm2]) are shaped Al-holder. The holder is mounted onto a Ti-disc. 826 (#2), 947 (#4), and 923 (#5), respectively. This cathode assembly is screwed to the plating cell body. Viton O-rings resistant to the organic liquids used 3.3. Preparation of thin layers by the “Drop-on- for MP serve as seals. Figure 1 shows a drawing of the Demand” (DoD) technique cell body, of the cathode assembly and of the completed cell. A Pd foil serves as the counter electrode. Water- The so-called Drop-on-Demand technique, which is e.g., cooled cylindrical Ti blocks (not shown in Figure 1) act applied in ink-jet printers, is widely used in research and as cathode and anode, respectively. industry. As an alternative technique to MP we currently Prior to deposition each batch (see section 3.1) was explore the feasibility of the DoD-technique for the evaporated to dryness, fumed with concentrated HNO3 production of thin lanthanide and actinide layers. Single and dissolved in 2 mL 0.5 M HNO3. For the production drops with volumes down to some tens of nL are of a target an aliquot of 1-1.2 mL (containing about 14- distributed onto various substrates using a commercially 16 mg 242Pu) was evaporated to dryness in a Teflon available ink-jet print head (BioFluidix type PipeJet P9) beaker and subsequently transferred into the deposition mounted together with an x-y translation-table cell with 2 x 100 µL 0.1 M HNO3. The cell was then (Thorlabs, type KMTS50E/M) for precise positioning of filled with a mixture of 9 mL isopropanol and 67 mL substrate with a lateral resolution of about 2 µm. The isobutanol. The mixture was stirred for 10 min using an printer can handle any solution with a viscosity in the ultrasonic mixer [13]. Deposition was performed within range of 0.5 - 500 mPa·s and a surface tension between two hours at a constant current of 15 mA and a voltage 30 - 76 mN/m. Thus, the method is not restricted to ranging from 300-400 V (floating). During the aqueous solutions only but also applicable with organic deposition process ultrasonic mixing was continued. solvents like isopropanol or isobutanol [14]. Deposition yields approaching 100 % were achieved as determined by α-particle spectroscopy. For this, an aliquot of 10 µL of the supernatant solution was taken from the deposition cell prior to and subsequent to deposition in order to prepare samples for α-particle counting.

Fig. 3. View of the DoD printing system consisting of the piezo dispenser (1) and two compact motorized translation stages (2) with a holder for substrates with a diameter of 26 mm (3). Fig. 1. Cell used for Molecular Plating of Pu. (a) plating cell body made of Kel-F™, (b) cathode assembly with Ti/Al Currently, investigations are performed to deposit deposition substrate, (c) completed plating cell. lanthanide compounds onto various substrates, including graphene foils. RI, Scanning Electron Microscopy and Atomic Force Microscopy are used to study 80

homogeneity and morphology of the layers produced by 12. A.Vascon, N. Wiehl, T. Reich, J. Drebert, K. the DoD technology. Among other applications, e.g., to Eberhardt, Ch.E. Düllmann, Nucl. Instrum. Meth. fabricate samples for neutron activation studies it is A721 (2013) 35-44 planned to produce thin 252Cf-layers on various 13. A. Vascon, J. Runke, N. Trautmann, B. Cremer, K. substrates as calibration sources and for studies of Eberhardt, Ch.E. Düllmann, Appl. Rad. Isot. 95 nuclear fission. Figure 3 shows a picture of the DoD (2015) 36-43 printing set-up. 14. R. Haas, S. Lohse, Ch.E. Düllmann, K. Eberhardt, C. Mokry, J. Runke, Nucl. Instrum. Meth. Phys. Res. A874 (2017) 43-49 References 1. D.J. Hinde, M. Dasgupta, D.Y. Jeung, G. Mohanto, E. Prasad, C. Simenel, J. Walshe, A. Wahkle, E. Williams, I.P. Carter, K.J. Cook, S. Kalkal, D.C. Rafferty, R. du Rietz, E.C. Simpson, H.M. David, Ch.E. Düllmann, J. Khuyagbaatar, EPJ Web of Conferences 131 (2016) 04004 2. M. Götz, S. Götz, J.V. Kratz, Ch.E. Düllmann, Ch. Mokry, J. Runke, P. Thörle-Pospiech, N. Wiehl, M. Schädel, J. Ballof, H. Dorrer, J. Grund, D. Huber, E. Jäger, O. Keller, J. Krier, J. Khuyagbaatar, L. Lens, B. Lommel, M. Mendel, K.J. Moody, P. Scharrer, B. Schausten, D. Shaughnessy, M. Schmitt, J. Steiner, N.Trautmann, A.Yakushev, V.Yakusheva, Nuclear Physics A961 (2017) 1–21 3. J. Klug, E. Altstadt, C. Beckert, R. Beyer, H. Freiesleben, V. Galindo, E. Grosse, A.R. Junghans, D. Légrády, B. Naumann, K. Noack, G. Rusev, K.D. Schilling, R. Schlenk, S. Schneider, A. Wagner, F.-P. Weiss, Nucl. Instrum. Meth. A577 (2007) 641-653 4. C. Guerrero for the CERN n_TOF collaboration, Eur. Phys. J. A 49 (2013) 27 5. G. Sibbens, A. Moens, R. Eykens, D. Vanleeuw, F. Kehoe, H. Kühn, R. Wynants, J. Heyse, A. Plompen, R. Jakopic, S. Richter, Y. Aregbe, J. Radioanal. Nucl. Chem. 299 (2014) 1093-1098. 6. B. R. Beck, J. A. Becker, P. Beiersdorfer, G. V. Brown, K. J. Moody, J. B. Wilhelmy, F. S. Porter, C. A. Kilbourne, and R. L. Kelley Phys. Rev. Lett. 98 (2007) 142501-142504 7. L. von der Wense, B. Seiferle, M. Laatiaoui, J.B. Neumayr, H.-J. Maier, H.-F.Wirth, C. Mokry, J. Runke, K. Eberhardt, Ch.E. Düllmann, N.G. Trautmann, P.G. Thirolf, Nature 533 (2016) 47-51 8. J.E. Evans, R.W. Lougheed, M.S. Coops, R.W. Hoff, E.K. Hulet, Nucl. Instrum. Meth. 102 (1972) 389-401 9. N. Trautmann, H. Folger, Nucl. Instrum. Meth. A282 (1989) 102-106 10. K. Eberhardt, W. Brüchle, Ch.E. Düllmann, K.E. Gregorich, W. Hartmann, A. Hübner, E. Jäger, B. Kindler, J.V. Kratz, D. Liebe, B. Lommel, H.-J. Maier, M. Schädel, B. Schausten, E. Schimpf, A. Semchenkov, J. Steiner, J. Szerypo, P. Thörle, A. Türler, A. Yakushev, Nucl. Instrum. Meth. A590 (2008) 134-140 11. D. Liebe, K. Eberhardt, W. Hartmann, T. Häger, A. Hübner, J.V. Kratz, B. Kindler, B. Lommel, P. Thörle, M. Schädel, J. Steiner, Nucl. Instrum. Meth. A590 (2008) 145-150 81

47 mg of 239Pu in a fission chamber for prompt fission neutron spectra measurements

B. Laurent1,*, G. Bélier1, A. Chatillon1, P. Marini1, J. Taieb1, A. Moens2, G. Sibbens2 and D. Vanleeuw2

1 CEA, DAM, DIF, F-91297 Arpajon, France

2 European Commission – Joint Research Centre – Directorate for Nuclear Safety and Security, 2440 Geel, Belgium

1 Prompt fission neutron spectra

1.1. Motivations, interests Among nuclear data needed for nuclear reactor design, prompt fission neutron energy spectra occupy a key position. They are essential for reliable predictions of nuclear criticality calculations for conventional reactors, fast neutron induced systems as well as for nonproliferation applications. However, experimental data, on which theoretical models and evaluations are adjusted, are scarce and present very significant discrepancies, especially in the low energy range (< 1 MeV). Moreover, the precision of our current knowledge of these observables is far less good than that of other fission observables, such as neutron multiplicity or Fig.1. Schematic description of the experimental principle. fission cross-sections. In order to improve the numerical modeling of the present and future nuclear systems, it is essential to perform new precise measurements. 2 The fission chamber

1.2. Experiment principle The chamber was specially designed to match the PFNS measurement constraints. All sources of neutron The experimental principle (cf. Fig. 1) is based on the scattering were minimized to limit the neutron spectra double time-of-flight method. A multiplate fission distortion associated to the parasitic reactions. The chamber, specially developed and containing 47 mg of principle of the chamber was the same than that of the 239Pu in 22 deposits, is placed in the collimated neutron previous 238U chamber described in details in References beam of WNR facility at LANSCE, Los Alamos [2], but the 239Pu chamber was developed in order to National Laboratory, Los Alamos, in the center of the improve the assembly of the deposits in a gloves box, Chi-Nu neutron detectors array [1]. The incident neutron due to the high activity. energy is measured between the HF signal coming from the accelerator and the signal extracted from the fission 239 chamber, while the fission neutron energies is measured 3 The Pu deposits between the fission chamber and Chi-Nu neutron The 239Pu mass was divided into 22 deposits of 2.1 mg detector signals. The use of a neutron pit and the walls each, with a diameter of 33 mm (areal density of 250 far enough from the setup reduce the amount of scattered µg/cm²). Each anode collects the signal from two neutrons and allow for a low background level in the deposits for a total of 10 MBq per channel. These data. deposits were electrodeposited on an aluminum foil glued on a frame. 239Pu deposition and mounting of the electrodes in the fission chamber, as shown in the Fig. 2,

* Corresponding author: [email protected] 82

was realized at the Target Preparation Laboratory of the European Commission – Joint Research Centre – Directorate G (EC-JRC.G.2) in Geel, Belgium.

Fig.2. Picture of one of the deposits and the full stack of electrodes mounted in the fission chamber.

Details of the 239Pu fission chamber and the mounting at JRC will be described. This chamber is currently used with the Chi-Nu neutron detector array at LANSCE/WNR neutron source facility and first results of the experiment will be presented.

References 1. R. C. Haight, H. Y. Lee, T. N. Taddeucci, J. M. O’Donnell, B. A. Perdue, N. Fotiades, M. Devlin, J. L. Ullmann, A. Laptev, T. Bredeweg, M. Jandel, R. O Nelson, S. A. Wender, C.-Y. Wu, E. Kwan, A. Chyzh, R. Henderson, and J. Gostic, Proceedings of the 2nd International Workshop on Fast Neutron Detectors and Applications, Ein Gedi, Israel November 6-11, 2011, ed. A. Buffler, JINST 7, C03028 (2012). 2. J. Taieb, B. Laurent, G. Bélier, A. Sardet, C. Varignon, Nucl. Inst. Methods Phys. Res. A 833, 1 (2016).

83

Investigation of the surrogate-reaction method via inelastic- scattering reactions on 240Pu

R. Perez-Sanchez1, B. Jurado1,*, D. Denis-Petit1, L. Mathieu1, I. Tsekhanovich1, V. Meot2, O. Roig2, O. Bouland3, M. Aiche1, L. Audouin4, C. Cannes4, S. Czajkowski1, S. Delpeche4, A. Goergen5, G. Kessedjian6, J. Mottier4, K. Nishio7, D. Ramos4, S. Siem5 and F. Zeiser5

1 CENBG, Bordeaux-Gradignan, France

2 CEA-DAM, Bruyères-le-Châtel, France

3 CEA-DEN, Cadarache, France

4 IPN, Orsay, France

5 University of Oslo, Norway

6 LPSC, Grenoble, France

7 Japan Atomic Energy Agency, Tokai, Japan

The surrogate-reaction method is an indirect method for nucleus, 240Pu, which is expected to have a stronger determining neutron-induced cross sections of short- sensitivity to the populated angular momentum and shall lived nuclei [1]. It is based on the measurement of decay help us to better understand its role in the fission probabilities induced by alternative or surrogate probabilities. In addition, it will be possible to compare reactions (transfer or inelastic scattering) and on the our results with directly measured neutron-induced data assumption that the decay probabilities of the compound for n+239Pu, which are very well known. nuclei formed in these reactions are equal to the neutron- In this contribution, we will present the surrogate induced probabilities. Most models predict a significant method, the experimental procedure and the first results. dependence of the fission and gamma-emission probabilities on the angular momentum J and parity π of the decaying nucleus. Since neutron-induced and References π surrogate reactions populate different initial J 1. J. Escher, et al., Rev. Mod. Phys. 84, 353 (2012). distributions, large differences between the decay 2. G. Kessedjian, et al., Phys. Lett. B 692, 297 (2010). probabilities induced by neutron absorption and by 3. G. Boutoux, et al., Phys. Lett. B 712, 319 (2012). surrogate reactions are expected. However, previous 4. Q. Ducasse, et al., Phys. Rev. C 94, 024614 (2016). works show that the fission probabilities induced by surrogate reactions are in good agreement with the neutron-induced ones, whereas there are very large discrepancies between the gamma-emission probabilities [2-4]. Additional and dedicated measurements are needed to fully understand this finding. We have recently performed an experiment to simultaneously measure fission and gamma-emission probabilities induced by (4He,4He’) and (3He,3He’) reactions on a 240Pu target. The 240Pu target was produced by the radiochemistry group of the IPN of Orsay in France with 240Pu material originating from the JRC-Geel. The inelastic-scattering reactions investigated are highly interesting for two reasons: They allow us to investigate for the first time an even-even fissioning

* Corresponding author: [email protected] 84

Nuclear Data at n_TOF

F. Mingrone1*, E. Chiaveri1, on behalf of the n_TOF Collaboration

1 European Organization for Nuclear Research (CERN), Geneva, Switzerland

1 Introduction flux of EAR2 allows to measure the cross-sections of very low mass samples (<1 mg), and reactions with The neutron time-of-flight facility of CERN, called small cross-sections or highly radioactive samples [4]. n_TOF, became operative in 2001, based on an idea by The excellent characteristics of the facility given, a C. Rubbia et al. [1], and since then it occupies a major fundamental feature for the measurement’s success is the role in the field of neutron cross-section measurements. high quality of the sample. To decrease as much as Thanks to the time-of-flight method, point-wise cross- possible systematic uncertainties, highly enriched sections can be measured in a broad energy range from metallic samples are always preferable. Moreover, a thermal up to GeV with a very high energy-resolution. precise characterization of the number of atoms is The facility ran from 2001 to 2004 (n_TOF Phase-1) essential, since it constitutes one of the main source of and, after a four years halt due to technical problem uncertainty. related to the neutron-producing target, it resumed operation at the end of 2008 till the end of 2012 (n_TOF Tab.1. Characteristics of the two n_TOF experimental areas Phase-2). During the Long Shutdown 1 (LS1) of CERN EAR1 EAR2 a second short 20 m flight-path [2], complementing the Energy 10-2 eV – 1 GeV 10-3 eV – 300 MeV existing 185 m one, has been constructed from May range 2013 and completed on the 25th of July 2014, starting Neutron 105 n/cm2/pulse 106 n/cm2/pulse the n_TOF Phase-3. flux Repetition During the operation of the facility, almost a hundred < 0.8 Hz (1 pulse/2.4s max) reactions have been measured, distributed into (n,γ), (n,f) rate Energy and (n,cp). The samples for many of these measurements 3.2 10-4 @ 1 eV 4.0 10-3 @ 1 eV resolution have been produced at the JRC-Geel laboratories. The 5.3 10-3 @ 1 MeV 4.0 10-2 @ 1 MeV (∆E/E) most significant measurements will be here described, and the future plans and perspectives presented.

3 Reference measurements 2 The n_TOF facility The precise characterization of the neutron flux, as well The pulsed neutron beam at n_TOF is produced by as a continue monitoring of the incident neutron beam, is spallation of 20 GeV/c protons from the CERN Proton mandatory to achieve the accuracy and precision Synchrotron accelerator on a water-cooled lead target required for cross-section measurements. To this [3]. The pulsed neutron source is used together with a purpose, the neutron flux at n_TOF has been fully moderation system, so that the n_TOF neutron beam investigated using several detection systems to cover the covers about eleven orders of magnitude in energy from entire neutron energy range, both in EAR1 [5] and EAR2 thermal to GeV in the first experimental area (EAR1), [6]. The results of these evaluations are shown in Fig. 1, and from cold neutrons to hundreds of MeV in the where an increase at the second experimental area in second experimental area (EAR2). average of a factor 40 can be seen. As can be seen from Table 1, thanks to their In addition, the neutron flux is continuously monitored complementary characteristics the two experimental during measurements exploiting the very well-known areas can be exploited to cover a wide range of cross sections of 6Li(n,α), 10B(n, α), 235U(n,f) and experimental cases. While EAR1 is best suited for high- 238U(n,f) reactions. All those materials, apart from the precision measurements, e.g. to study the resolved 6LiF, are produced and characterized by JRC-Geel, and resonance region, and to extend experimental data to can be used either as samples in monitoring detectors very high neutron energy, the 40 times higher neutron

* Corresponding author: [email protected] 85

Fig.2. 240Pu (left) and 237Np (right) samples.

oxide material was electro-deposited on a 250 µm-thick aluminum backing with a diameter of 5 cm, while the deposit itself had a diameter of 3 cm. Pictures of the Fig.1. Comparison between the evaluated neutron flux in EAR2 samples are shown in Fig. 2. (blue) and in EAR1 (red). The increase at the new measuring station is on average a factor 40. Figure from [6]. In addition to the Pu and Np samples, in both measurements 235U and 238U material have been inserted (e.g. low-mass MicroMegas), or as reference samples to in the stack and measured as reference samples. be measured in the same detection setup used for (n,f) or (n,cp) measurements. 4.2. Data reduction Both the data sets have been analyzed exploiting a Pulse 4 Fission measurements Shape Analysis routine [12] to determine the amplitude and the position in time of every recorded signal. The During the n_TOF Phase-3, six neutron-induced fission contribution of the α-activity as well as spontaneous reaction measurements have been performed up to now, fission events have been evaluated from beam-off and two more are foreseen for 2018. Among them, the 240 237 measurements. To reach the high-energy region, the Pu(n,f) and the Np(n,f) cross-section have been γ measured in the second experimental area using metallic effects due to the relativistic particles burst - called - samples produced at JRC-Geel in Belgium [7,8]. Both flash - has been extensively studied. Moreover, the these reactions play a very important role in the detector dead time, as well as the background development of new nuclear technologies. In fact, both contribution due to sample impurities were taken into isotopes are among the major long-lived components of account during the analysis. In Fig. 3 preliminary results of the 240Pu(n,f) cross-section (top, from Ref. [13]) and nuclear wastes, and have been therefore targeted as 237 potential incinerators in fast neutron reactors. the Np(n,f) count rate (bottom) as a function of the incident neutron energy are shown.

4.1. Experimental setup The detection system for the 240Pu(n,f) and the 237Np(n,f) consists of a stack of low-mass MicroMegas detectors [9] with Micro Bulk fabrication process [10]. Six detectors are housed in a compact fission chamber, and operated with an Ar (88%) + CF4 (10%) + isoC4H10 (2%) gas mixture at atmospheric pressure. The great advantage of performing these measurements in EAR2 consists in the largely improved signal to background ratio: thanks to the very high instantaneous neutron flux intensity the necessary statistics could have been accumulated in a relatively short time, preventing the detectors to be damaged - and their performances significantly affected - by the high activity of the samples.

4.1.1 Samples

For the 240Pu(n,f) measurement, three high purity (99.89% atomic abundance) plutonium dioxide (PuO2) samples, prepared at JRC-Geel [11], were used having a total 240Pu mass of 2.288 mg (~100 µgr/cm2 per sample) α 237 and a total -activity of 19.219 MBq. For the Np(n,f) measurement, four neptunium hydroxide (H5NpO5) with 240 237 Fig.3. Pu(n,f) cross section (top) in the high-energy region 10 kBq activity per sample were used, for a total Np and 237Np(n,f) count rate (bottom) in the whole energy 2 mass of about 2 mg (~50 µgr/cm per sample). The spectrum. Courtesy of A. Stamatopoulos. 86

5 Charged-particle emission measurements

With the construction of the second experimental area, the physics program of the facility opened more and more towards (n,cp) reaction measurements. Since their cross-section is normally very low, and it is not possible to use thick samples, the measurements substantially benefit from the very high neutron flux of EAR2. In this context, the neutron destruction reactions on radioactive 26Al, 26Al(n,p) and 26Al(n,α), have been measured in 2016 at stellar neutron energies [14]. These reactions have been identified as the main uncertainties to predict 26 the galactic Al abundance, since only few experimental Fig.5. Count rate spectrum for the 6Li(n,α) reaction. Courtesy of data exist and they exhibit severe discrepancies. S. Lonsdale.

been processed with a new moving window 5.1. Experimental setup deconvolution (MWD) algorithm to extract the needed parameters from the raw data. Fig. 5 shows a counting Protons and alpha particles are detected by single sided 6 silicon strip detectors arranged as ∆E-E telescope (20 spectrum measured with a LiF sample. 26 α µm and 50 µm thickness, respectively), allowing particle Alpha particles from Al(n, ) reaction can be clearly identification. Both the E and ∆E detectors have a spatial identified in a deposited-energy vs incident-neutron ∆ resolution of 3 mm along one axis. In Fig. 4 the energy plot. In addition, the coincidence between E and detection system is shown. A 6-way transparent cross E detector allows additional efficient background vessel has been optimized for the detector operation with suppression and particle identification for proton events. thin light-tight windows and housing for a direct plug of The data analysis is still ongoing, and the preliminary the pre-amplifier. The ∆E-E detectors are placed in a results are very promising. distance of about 4 cm from the Al sample. 6 Capture measurements Neutron-induced capture cross-section measurements have always occupied a major role in the physics program of the n_TOF facility. During the Phase-2 campaign, a new method, called fission tagging, has been tested to improve the discrimination of background due to fission γ-rays, thus improving the quality of the (n,γ) data that can be obtained from fissile isotopes [17]. The technique combines the Total Absorption Calorimeter (TAC) with a fission chamber positioned in Fig.4. Left: picture of the vacuum vessel for the Si-telescope its center. In this way, the anti-coincidence between γ- mounted in EAR2. Right: scheme of the inner setup, the rays detected in the calorimeter’s crystals and a fission neutron beam is out of the paper. event occurred in the fission chamber will isolate γ-rays coming only from capture reactions. 5.1.1 Samples After the proof-of-concept performed with 235U, the improved method has been used in 2016 to measure the 26 The highly enriched Al sample used was produced by 233U(n,γ) cross section [18]. This reaction plays a JRC-Geel in collaboration with LANSCE [15]. The fundamental role in the Th-U fuel cycle, and it was 26 sample was prepared by electrodeposition of Al on a inserted in the “NEA High Priority Request List” with thin Ni backing 7.5 µm thick. The active area is 50 × 60 the aim of extending the neutron energy range with a 2 17 26 mm , for a total of (2.60 ± 0.12) × 10 atoms of Al target accuracy that varies from 0.5% to 9%. [16]. The neutron fluence has been monitored by a 10B sample, 99% enriched, which is placed back-to-back 6.1. Experimental setup 26 6 with the Al. In addition, three 95% enriched LiF As previously mentioned, the method has been tested in samples have been measured to normalize the data to the 2011 using a MicroMegas as fission chamber in the 6 α well-known Li(n, ) cross section. centre of the TAC. Although the test was successful, above ~100 eV severe background issues were 5.2. Data reduction experienced because of the presence of Cu in the beam coming from MicroMegas electrodes. The preamplifier signals recorded with flash-ADCs has To improve the technique, a new compact multi-plate 87

Fig.6. Picture of the fission chamber mounted in the centre of the Total Absorption Calorimeter. The pre-amplifier can be seen as the green boards. fission chamber has been developed, housing 14 different samples. Dedicated fast preamplifiers have been directly plugged on the chamber (developed by CEA-DAM), with a time resolution of about 30 ns FWHM. At the same time, also the voltage dividers of the TAC have been improved, allowing an easier access to the hundreds of keV energy region. In Fig. 6 a picture of the fission chamber mounted in the TAC centre is shown. Fig.7. Top: preliminary count-rate spectra in the TAC for the 6.1.1 Samples (n,f) - blue curve - and (n,γ) - green curve. Courtesy of M. Bacak. Bottom: evaluated (n,f) and (n,γ) cross-sections. The high-purity samples - 99.936% of 233U - have been obtained by molecular plating at the JRC-Geel. 14 The analysis is still ongoing, but a preliminary count-rate unsealed spots of 4 cm diameter have been deposited on spectrum of (n,f) and (n,γ) reactions can be seen in Fig. a 10 µm Al backing, with a very compact geometry 7, obtained applying the coincidence and anti- needed for the fission chamber. The deposited material coincidence method, respectively. Apart from some has an average density of 264.5 µg/cm2, for a total mass deviation at thermal energies due to background issues, of 46.5 mg. the trend is following what expected from the Due to the very high activity of the samples (about 1.5 evaluations, showing therefore a very promising result. MBq/sample), the assembly of the samples in the fission chamber have been particularly challenging. Several tests have been done to identify the best procedure and 7 Future perspectives avoid any contamination of the chamber, which would The collaboration between the n_TOF facility and the have prevented the feasibility of the measurement. JRC-Geel laboratory for sample production has been very fruitful, as proven by the quality of the results 6.2. Data reduction obtained in the measurements previously described. In this context, two new samples will be prepared in The data set has been analysed with a dedicated Pulse 2018 to be measured at n_TOF: the 230Th and 241Am. Shape Analysis routine to extract the parameters from The importance of the 241Am(n,f) and 230Th(n,f) reactions the TAC raw data, while the signals from the fission spans from the nuclear technologies (waste chamber have been analysed with the general n_TOF transmutation and recycling scenarios, Th-U fuel cycles, PSA routine [12]. respectively) to improve the investigation of the fine A careful time-calibration has been done to correct for structures of fission model in 230Th. For both these the misalignment due to different electronic chains, so to isotopes the fission cross section will be measured with guarantee the reliability of the coincidence method. MicroMegas detectors covering the region at and above Moreover, an accurate energy calibration of the TAC is the fission threshold, and producing as well accurate data required to apply the total absorption detection method. for the sub-threshold and resonance regions [19,20]. Background events are significantly suppressed by applying the anti-coincidence method and reconstructing the capture cascade, but dedicated measurements have References been performed as well to take into account the contribution of the activity of the samples and of the 1. C. Rubbia et al., Tech. Rep. CERN/LHC/98-02, fission chamber itself. CERN (1998). 88

2. C. Weiß et al., Nucl. Inst. Meth. A 799, 90–98 (2015). 3. C. Guerrero et al., Eur. Phys. J. A 49, 27 (2013). 4. E. Chiaveri et al., Nucl. Inst. Meth. A 743, 79 (2014). 5. M. Barbagallo et al., Eur. Phys. J. A 49, 156 (2013). 6. M. Sabaté-Gilarte et al., Eur. Phys. J. A, accepted for publication. 7. A. Tsinganis et al., CERN-INTC-2014-051/INTC-P- 418 (2014). 8. L. Tassan-Got et al., CERN-INTC-2015-007/INTC- P-431 (2015). 9. Y. Giomataris et al., Nucl. Inst. Meth. A 376, 29 (1996). 10. S.Andriamonje et al., Journal of Instrumentation 5 (2010). 11. G. Sibbens et al., J. Radioanal. Nucl. Ch. 299, 1093 (2014) 12. P. Žugec et al., Nucl. Inst. Meth. A 812, 134 (2016). 13. A. Stamatopoulos et al., EPJ Web of Conferences 146, 04030 (2017). 14. C. Lederer et al., CERN-INTC-2014-006 / INTC-P- 406 (2014). 15. C. Ingelbrecht et al., Nucl. Instr. Meth. A 480, 114 (2002). 16. L. De Smet et al., Phys. Rev. C 76, 045804 (2007). 17. C. Guerrero et al., Eur. Phys. J. A 48, 29 (2012). 18. C. Carrapiço et al., CERN-INTC-2013-041 / INTC- P-397 (2013). 19. M. Diakaki et al., CERN-INTC-2017-009 / INTC-P- 493 (2017). 20. A. Tsinganis et al., CERN-INTC-2017-008 / INTC- P-492 (2017).

89

Fast neutron detector development for measurements at the VENUS-F reactor

1,* 1 2 2 3 1 1 Jan Wagemans , Peter Baeten , Annick Billebaud ,, Sebastien Chabod , Jan Heyse , Anatoly Kochetkov , Antonín Krása , F.-R. Lecolley4, J.-L. Lecouey4, G. Lehaut4, N. Marie4, Nadia Messaoudi1, Peter Schillebeeckx3, Goedele Sibbens3, David Vanleeuw3, and Guido Vittiglio1

1 Belgian Nuclear Research Centre SCK•CEN, Mol, 2400, Belgium

2 Laboratoire de Physique Subatomique et de Cosmologie, CNRS-IN2P3/UJF/INPG, France

3 Joint Research Centre, Geel, 2440, Belgium

4 Laboratoire de Physique Corpusculaire de Caen, ENSICAEN/Univ. de Caen/CNRS-IN2P3, France

1 Sub-criticality monitoring of ADS The source jerk technique requires that the accelerator delivers a continuous beam with short, periodical To support the design and licensing of the MYRRHA interruptions (called source jerks) onto a neutron ADS (accelerator driven system) [1], the GUINEVERE producing target in the sub-critical reactor core. facility was developed at the Belgian Nuclear Research The core reactivity (ρ) is determined by calculating Center SCK·CEN. The zero-power VENUS-F reactor [2] the ratio of the prompt neutron population np = n0 – n1 was coupled to the GENEPI-3C accelerator [3] making (measured during the time when the beam is on the up the world first lead-based fast ADS, see Fig.1. target) to the delayed neutron population nd = n1 GUINEVERE as a zero-power mockup of (measured during the interruptions of the accelerator MYRRHA ADS serves for investigation and validation beam, see Fig.2): of the sub-criticality measurement techniques. Among several investigated ones [4-9], the source jerk technique ρ − nn = ξ 01 , (1) [8] has been selected for the absolute sub-criticality βeff n measurement of the MYRRHA ADS. 1 β where ξ is the accelerator duty cycle factor and eff is the effective delayed neutron fraction. GENEPI-3C accelerator 90° bending The assumptions applied in the source jerk data ION SOURCE magnet analysis are based on point kinetics that is not valid in a (pulsed/ 220 kV D+, D +, D + sub-critical reactor. Therefore, spatial corrections need to continuous/ acceleration 2 3 beam trip) be applied to get correct reactivity values.

D+ 2 Detector choice for sub-criticality monitoring Tritium target The choice of neutron detector type and positioning is D + T → α + n (14 MeV) crucial for the sub-criticality monitoring. Fission chambers are seen to be the most promising candidate n Active zone for this purpose. Reflector Typical detector locations in the sub-critical 235 VENUS-F reactor VENUS-F reactor are indicated in Fig.3. The U (1 mg Fig.1. Schematic drawing of the VENUS-F + GENEPI-3C to 1 g) fission chambers are located in the active zone, at coupling (not on scale) making up a GUINEVERE ADS. the interface with the reflector, and in the reflector at various distances from the core.

* Corresponding author: [email protected] 90

Another considered alternative, a fission chamber with a 237Np deposit (available in pure form), was discarded due to high α-background in case of heavy (~1 g) 237Np deposit, which would be needed to reach sufficient counting statistics.

3 Development of a high-purity 238U fission chamber

The need to develop a fission chamber with an ultra-pure 238U deposit lead to the collaboration between SCK·CEN and JRC in Geel. JRC has a high-purity 238U base material of 99.998 at.% (i.e. two orders of magnitude purer than can be found in commercially available fission chambers). JRC Fig.2. Example of neutron detector count rates before, during prepared a sample of this material in a specific solution and after a source jerk (2 ms duration) with indicated (dissolution of U3O8 in HNO3 and complete drying). prompt+delayed (n0) and delayed neutron (n1) levels. The mass of uranium (1.484±0.029 g) and

UO2(NO3)2 (2.457±0.029 g) were determined by

weighing. The isotopic composition was determined reactor vessel

` Pb reflector using mass spectrometry by JRC-Geel. The characterstics of this fission chamber are listed in the last active zone row of Table 1.

238 CR beam line Table 1. Isotopic composition of the three U deposits used for manufacturing of the fission chambers. The first detector is target commercially available standard depleted, the second is high- CR purity deposit and the third one is ultra-pure deposit that is the experimental result of the presented work. The uncertainties are expanded channels combined standard uncertainties with a coverage factor of k=2.

Supplier of Enrichment [wt.%] deposit 234U 235U 236U 238U Photonis 0.0004 0.2016 0.001 99.797 Fig.3. Subcritical VENUS-F core with a neutron source located CEA 0.0003 0.035 - 99.964 in the center of the core. The experimental channels where JRC-Geel 0.000156(6) 0.0012(1) 0.00024(6) 99.99831(16) neutron detectors are located are indicated with white circles.

When the source jerk method is applied, the time evolution of the detector response strongly depends on the detector location. The 235U fission chambers are highly sensitive to thermalizing elements and need a long beam interruption for the neutron population to reach its delayed neutron level. Significant corrections need to be applied to get correct reactivity results [8]. This issue could be solved by the use of threshold detectors as they are not sensitive to local moderating elements and their response reaches the delayed neutron level quickly after the beam interruption. A commercially available fission chamber (manufactured by Photonis) with a depleted 238U deposit was also used at VENUS-F. However, the fission chamber contains a non-negligible amount of 235U (≈0.2%), which distorts the detector signal. Another 238U fission chamber was manufactured using deposit material obtained from CEA, which has one order of magnitude higher purity, see second row of Table 1. This fission chamber was also applied to the source jerk measurement at GUINEVERE. Its response improved compared to the depleted one but it did not reach the desired shape.

Fig.4. Scheme of the fission chamber, type CFUL01 [10]. 91

A new fission chamber in an aluminum body with a 4 Conclusion deposit length of 21.1 cm (Fig.4) was manufactured from this uranium solution. The 238U mass in the fission Combining the different fields of expertise available at chamber deposit is 1.15 g with a specific activity of 37.6 JRC-Geel and SCK•CEN in Belgium, a new fast neutron 238 kBq/g. A gas mixture Ar + 4 % N2 was used as the detector was developed. Using high-purity U base filling gas at 250 kPa. material available at JRC-Geel, a fission chamber was The new 238U fission chamber was calibrated in the manufactured, calibrated at the standard irradiation field standard irradiation field in the BR1 reactor at at the BR1 reactor and is currently applied to optimize SCK•CEN [11]. A measured fission fragment spectrum the sub-criticality measurement technique at the is shown in Fig.5. The comparison of the measurement GUINEVERE ADS. with the certified values will be presented.

References

1. G. Van den Eynde et al., “An updated core design for the multi-purpose irradiation facility

MYRRHA”, J. Nucl. Sci. Technol. (2015). Available online http://dx.doi.org/10.1080/00223131.2015.1026860

Count/chn 2. A. Kochetkov et al., “The Lead-Based VENUS-F Facility: Status of the FREYA Project”, EPJ Web of Conferences 106, 06004 (2016). 3. M. Baylac et al, Operation of the accelerator driving Channel the VENUS-F core for the low power ADS Fig.5. Fission fragment spectrum measured with the ultra-pure experiments GUINEVERE and FREYA at 238 U fission chamber at the BR1 irradiation field. SCK•CEN, Proceedings of TCADS-2, Nantes, May 2013 238 The new U fission chamber was applied in the 4. J. L. Lecouey et al, “Estimate of the Reactivity of source jerk measurements at GUINEVERE. Raw the VENUS-F Subcritical Configuration using a 238 measured responses of the three U fission chambers Monte Carlo MSM Method,” Annals of Nuclear (each of them at slightly different position in the Energy, 83 (2015) 65–75. reflector) are shown in Fig.6. The spatial correction 5. W. Uyttenhove et al, Methodology for modal factors and the quantification of the difference between analysis at pulsed neutron source experiments in the three detectors is under investigation and is planned accelerator-driven systems, Annals of Nuclear to be presented at the EUFRAT user meeting. Energy 72 (2014) 286-297. 6. A. Kochetkov et al, “An alternative Source Jerk method implementation for the subcriticality estimation of the VENUS-F subcritical core in the FREYA Project,” Proceedings of PHYSOR 2014, Kyoto, Japan, Sep 28 – Oct 3, 2014. 7. S. Chabod et al, “Reactivity measurements at GUINEVERE facility using the integral kp method,” Proceedings of PHYSOR 2014, Kyoto, Japan, Sep 28 – Oct 3, 2014. 8. T. Chevret et al, “Reactivity measurement of the lead fast subcritical VENUS-F reactor using beam interruption experiments,” Proceedings of PHYSOR 2014, Kyoto, Japan, Sep 28 – Oct 3, 2014. 9. N. Marie et al, “Reactivity monitoring using the area method for the subcritical VENUS-F core within the framework of the FREYA Project,” Proceeding of TCADS-2, Nantes, May 2013. 10. https://www.photonis.com/uploads/datasheet/ngd/C FUL01.pdf Fig.6. Time response of the three 238U fission chambers (see 11. J. Wagemans et al., “The 235U prompt fission Table 1) in the reflector of the sub-critical VENUS-F reactor neutron spectrum in the BR1 reactor at SCK•CEN,” of the GUINEVERE ADS facility. The accelerator was EPJ Web of Conferences 106, 06003, 2016. operated in continuous mode with periodic interruptions. The time interval of 0.3 ms before the source jerk and 1.2 ms during the source jerk are shown.

92

Measurements on U and Pu standards with medium resolution gamma-ray spectrometers

I. Meleshenkovskii1,2, A. Borella1,* R. Rossa1, A. Moens3, P. Schillebeeckx3, R. Wynants3

1 Belgian Nuclear Research Centre, SCK•CEN, Nuclear Science and Technology Group, Mol, Belgium

2 Université libre de Bruxelles, Service de Métrologie Nucléaire (CP/165/84)

3 European Commission Joint Research Centre, Retieseweg 111, B-2440 Geel, Belgium

1 Introduction 527, produced by GBS-Elektronik [2] and a data acquisition software WinSpec [3].

There is an interest in developing gamma-ray measuring The LaBr3 scintillator used was a 2×2 inch device devices based on the room temperature detectors such as fabricated by Saint-Gobain Crystals (France). The high- semiconductor detectors of the CdZnTe (CZT) type and voltage bias applied to the detector was 590 V. This scintillators of the LaBr3 type. This is true also for detector was used in an analogue spectroscopy signal safeguards applications and the International Atomic processing chain consisting of a charge sensitive Energy Agency (IAEA) has launched a project to assess preamplifier, linear amplifier and shaper, analogue-to- medium resolution gamma-ray spectroscopy for the digital converter and a data acquisition software determination of the isotopic composition of U and Pu DAQ2000 developed in LabView. bearing samples. This project is carried out within the Non-Destructive Assay Working Group of the European Safeguards Research and Development Association 2.2. Samples (ESARDA). For uranium measurements we used certified uranium The Belgian nuclear research centre, SCK•CEN, is a CBNM (Central Bureau for Nuclear Measurements) long-standing member of ESARDA and has experience standards of five different enrichment values: 0.31%, in Non-Destructive Assay methods applied to the 0.71%, 1.94%, 2.95% and 4.46%. These samples are safeguards of nuclear material. One of the activities is to indicated as CBNM Nuclear Reference Material 271 in develop an analysis code for medium resolution spectra Ref. [4]. applied to the verification of nuclear material. 3 For plutonium measurements we used certified In this framework measurements with 500 mm CZT plutonium CBNM standards of four different isotopic × detector and a 2 2 inch LaBr3 on sets of U and Pu compositions as indicated in table 1. These samples are CBNM standards were carried out at the European indicated as EC-NRM-171/NBS-SRM-969 in Ref. [4]. Commission Joint Research Center (Geel, Belgium). In this work we report about the results of the measurements campaign. 2.3. Collimators and attenuators In order to reduce the impact of scattered photons 2 Experimental setup reaching the detector from the sample and nearby materials, the measurements were conducted with lead collimators. The uranium samples were positioned 2.1. Detectors and electronics directly on the top surface of the lead collimators for which there were bored seats 81 mm in diameter and 5 The used CZT detector was a 10 mm × 10 mm × 5 mm mm deep. The sample-to-detector distance was 20 mm. (500 mm3) device of a hemispheric design by RITEC Measurements of plutonium certified standards were [1]. The high-voltage bias applied to the detector was conducted in two configurations – with and without lead 1400 V. The CZT detector was used in a digital collimators on both detectors to investigate their impact instrumentation measurement chain consisting of a on the spectra quality. Plutonium standards were digital multi-channel-analyzer (MCA) module, model positioned in adjustable height holders above the

* Corresponding author: [email protected] 93

detectors. To reduce the impact of 241Am 59 keV gamma line on plutonium spectra we used a set of cadmium (1.5 mm thick) and copper (0.5 mm thick) attenuators.

CBNM Mass percent* Sample 238Pu 239Pu 240Pu 241Pu 242Pu 241Am/Pu Pu93 0.0117 93.4123 6.3131 0.2235 0.0395 0.1047 Pu84 0.0703 84.3377 14.2069 1.0275 0.3576 0.2173 Pu70 0.8458 73.3191 18.2945 5.4634 2.0772 1.1705 Pu61 1.1969 62.5255 25.4058 6.6793 4.1925 1.4452 Table 1: Isotopic composition of plutonium standards (*on 1986).

Examples of spectra acquired with the CZT detector are given in Fig. 1 and Fig. 2. 3 Results 107 For the measurements of uranium and plutonium EC NRM 271 standards we used 1.2 µs pulse shaping time constant for 106 Pu93 the CZT detector on the digital MCA and 0.25 µs pulse Pu61 shaping time constant for the LaBr3. These settings 105 allowed to achieve good throughput of the analogue pulse processing chain coupled with the LaBr3 detector 104 considering its high efficiency and to minimize the deadtime to less than 2% on the CZT detector coupled Counts 103 with the digital MCA. The measurements were carried out in runs of 7200 seconds each. 102 To investigate the time stability of the measurement 101 chain of both CZT and LaBr3 detectors we evaluated the following parameters for each measurement run: peak 100 centroid, FWHM, net peak area and net peak area 0 250 500 750 1000 1250 1500 1750 uncertainty. For each measured standard we calculated the mean Energy / keV value of the observed net peak area values for all Fig.1. Pu spectra on two samples of the CBNM Nuclear Reference Material 271 measured with the CZT detector measurement runs and set the minimum and maximum limits for the net peak area values in corresponding 105 Region Of Interest (ROI) based on the two sigma EC NRM 171 interval around that mean value, allowing to reject poor 235 U enrichment quality spectra with a 95.5% confidence interval. In addition maximum centroid drift of ±1 channel for the 104 4.46% 185.7 keV gamma-line of 235U and ±2 channels for the 0.71% 413.4 keV gamma-line of 239Pu were adopted. Spectra that satisfy the criteria were used to produce the 103 summed spectrum file for each given standard.

The results of uranium measurements indicate that both Counts detectors showed quite strong gain drift, especially 2 during the long-term measurements of low enriched 10 uranium standards. The observed fluctuations of the net peak area values in the ROI corresponding to the 185.7 235 keV gamma-line of U were smaller. 101 The results of plutonium measurements indicate strong 0 200 400 600 800 1000 gain drift on the LaBr3 detector coupled with the Energy / keV analogue instrumentation. Thus, the number of rejected measurement runs was higher for the LaBr detector in Fig.2. U spectra on two samples of the EC-NRM-171/NBS- 3 SRM-969 reference material measured with the CZT detector comparison with the CZT detector. CZT detector coupled with the digital MCA showed better stability in measurements with and without lead collimators during the measurements of plutonium standards. 94

4 Conclusions

Measurements of uranium and plutonium certified standards were conducted on two detectors – a 500 mm3

CZT semiconductor detector and a 2×2 inch LaBr3 scintillator. The stability of the whole measurement chain both for CZT and LaBr3 detectors during the measurements was evaluated by determining the following parameters for each measurement run: peak centroid, FWHM, net peak area and net peak area uncertainty. The results of this study will be further used for the development of a uranium and plutonium isotopic composition determination algorithm particularly suited for CZT and LaBr3 detectors for safeguards applications. The produced spectra of uranium and plutonium standards will be added to the ESARDA database.

Acknowledgements

The would like to thank the JRC for its support to this measurement campaign through the transnational access programme EUFRAT. In addition, this work is carried out in the framework of a PhD programme sponsored by Belgonucleaire NV and Tecnubel NV in the framework of the contract AC-2015- 002 between SCK•CEN, Belgonucleaire NV and Tecnubel NV.

References

1. V. Ivanov et al, “Performance Evaluation of New Generation CdZnTe Detectors for Safeguards Applications”, 2014. 2. MCA-527 user manual, update 2012-08-07, GBS- Elektronik GmbH, Großerkmannsdorf, Germany, 2012. 3. https://www.gbs- elektronik.de/en/downloads/downloads-nuclear- measurements.php 4. S.-T. Hsue, J. E. Stewart, T. E. Sampson, G. Butler, C. R. Rudy, P. M. Rinard, “Guide to Nondestructive Assay Standards: Preparation Criteria, Availability, and Practical Considerations”, Los Alamos Report LA-13340-MS, 1997

95 Participants of EUFRAT user meeting Name Organisation Email ANGELONE Maurizio ENEA, Italy [email protected]

BANDAC Iulian Laboratorio Subterraneo de Canfranc (LSC), Spain [email protected] BERTHOUMIEUX Eric CEA Irfu- Université Paris Saclay, France [email protected] BUCALOSSI Andrea Joint Research Centre - Brussels, Belgium [email protected]

CAPOTE Roberto IAEA, Vienna [email protected] CHARRETTE Matthew Woods Hole Oceanographic Institution, USA [email protected] CROYMANS Tom Universiteit Hasselt - Campus Diepenbeek, Belgium [email protected]

DE FELICE Pierino ENEA, Italy [email protected] DESSAGNE Philippe CNRS, France [email protected]

EBERHARDT Klaus Johannes Gutenberg-Universität, Germany [email protected]

FENYVESI András Hungarian Academy of Sciences, Hungary [email protected] FIORE Salvatore ENEA, Italy [email protected]

GOOK Alf Joint Research Centre - Geel, Belgium [email protected]

HAMBSCH Franz-Josef Joint Research Centre - Geel, Belgium [email protected] HEYSE Jan Joint Research Centre - Geel, Belgium [email protected] HOREMANS Nele Belgian Nuclear Research Centre (SCK-CEN), Belgium [email protected] HULT Mikael Joint Research Centre - Geel, Belgium [email protected]

IANNI Aldo Laboratorio Subterraneo de Canfranc, Spain [email protected]

JACQMIN Robert CEA, France [email protected] JANSSON Kaj Uppsala university, Sweden [email protected] JUNGHANS Arnd Helmholtz-Zentrum Dresden-Rossendorf, Germany [email protected] JURADO Beatriz CENBG, France [email protected]

KERVENO Maëlle CNRS- IPHC, France [email protected] KIRSCH Andrea Max-Planck-Institut fuer Kernphysik, Germany [email protected] KOPECKY Stefan Joint Research Centre - Geel, Belgium [email protected] KRASA Antonin SCK-CEN, Belgium [email protected] 96 Participants of EUFRAT user meeting Name Organisation Email LAURENT Benoit CEA/DAM/DIF, France [email protected] LEAL Luiz Institut de Radioprotection et de Surete Nucleaire, France [email protected] LECONTE Pierre CEA, France [email protected] LEHNERT Björn Carleton University, Canada [email protected]

MELESHENKOVSKII Iaroslav SCKCEN, Belgium [email protected] MINGRONE Federica CERN, Switzerland [email protected] MONDELAERS Wim Joint Research Centre - Geel, Belgium [email protected]

NYMAN Markus Joint Research Centre - Geel, Belgium [email protected]

OBERSTEDT Andreas Extreme Light Infrastructur-Nuclear Physics, Romania [email protected] OBERSTEDT Stephan Joint Research Centre - Geel, Belgium [email protected] OLACEL Adina-Adriana Horia Hulubei National Institute (IFIN-HH), Romania [email protected]

PARADELA DOBARRO CarlosJoint Research Centre - Geel, Belgium [email protected] PARTY Eliot CNRS, France [email protected] PILLON Mario ENEA, Italy [email protected] PLOMPEN Arjan Joint Research Centre - Geel, Belgium [email protected] POMP Stephan Uppsala university, Sweden [email protected]

ROSSA Riccardo SCK-CEN, Belgium [email protected]

SALAMON Lino CEA CADARACHE, France [email protected] SCHILLEBEECKX Peter Joint Research Centre - Geel, Belgium [email protected] SCHROEYERS Wouter Universiteit Hasselt, Belgium [email protected] SEROT Olivier CEA CADARACHE, France [email protected] SIBBENS Goedele Joint Research Centre - Geel, Belgium [email protected] SCHREURS Sonja Universiteit Hasselt, Belgium [email protected]

TAGLIENTE Giuseppe INFN, Italy [email protected] TAUCER Fabio Joint Research Centre - Brussels, Belgium [email protected] TRETYAK Volodymyr National Academy of Sciences of Ukraine, Ukraine [email protected]

VANDERHEYDEN Sara Universiteit Hasselt, Belgium [email protected] VANLEEUW David Joint Research Centre - Geel, Belgium [email protected]

WAGEMANS Jan SCK-CEN, Belgium [email protected] WEISS Christina CIVIDEC Instrumentation GmbH, Germany [email protected]

ZEROVNIK Gasper Joint Research Centre - Geel, Belgium [email protected] 97

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