DOCSLIB.ORG

Total Cross-Sections of U, UO2 and Tho2 for Thermal and Subthermal Neutrons

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Total Cross-Sections of U, UO2 and Tho2 for Thermal and Subthermal Neutrons AF-999 UDC 539.125.5.164.078 CM CN CN UJ Total Cross-Sections of U, UO2 and ThO2 for Thermal and Subthermal Neutrons S. F. Beshai AKTIEBOLAGET ATOMENERGI STOCKHOLM, SWEDEN 1966 A.E-222 TOTAL CROSS-SECTIONS OF U, UO AND ThO. 2 ~2 FOR THERMAL AND SUB THERMAL NEUTRONS Samir F. Beshai SUMMARY The total neutron cross-sections of U, UO_ and ThO~ have been measured from 0.0045 eV to 0.028 eV, using the time-of-flight techni- que. The samples were measured at 20 C. ThO? was also measured at 750 C. The neutron source was the reactor Rl, Stockholm. The experimental results presented as graphs in the report show in detail the influence of Bragg scattering. The results further show that the increase of the temperature for the ThO? sample gives an in- crease in the cross-section. The work also contains some calculations of the position in energy of Bragg edges for the three materials. These calculations show a very good agreement with the experiments. For uranium metal some cal- culations have been carried out also for the height (o*ifvi) of the edges. The agreement with the experiments is reasonable. * IAEA-fellow from Atomic Energy Establishment, United Arab Republic. Printed and distributed in March 1966 LIST OF CONTENTS Page 1. Introduction 3 2. Experimental equipment 3 3. Measurements and results 4 3.1 Uranium 4 3.2 Uranium oxide 6 3. 3 Thorium oxide 6 Acknowledgements 7 References 8 Tables Figures - 3 - 1. INTRODUCTION Work has been started at the reactor Rl on the measurement of the total cross-section of U, UO_, Th and ThO,, for thermal and subthermal neutrons. These measurements are carried out with time-of-flight technique for micro-crystalline (or almost micro- crystalline) samples from 20 C to 800 C. The work at high tem- perature especially will produce some new results. The experiment has some connection with reactor physics, because) besides the absorption» the scattering cross-section will enter in the build-up of fuel element spectra. " Furthermore, from a pure physics viewpoint it is interesting and instructive to study the effect on the cross-section of various Bragg reflections. This report deals with measurements on U, UO, and ThO.,. Some calculations of the position and height of various Bragg edges are also included. 2. EXPERIMENTAL EQUIPMENT Most of the measurements were carried out with a fast chopper, the properties of which are described in [l] « Some experiments with a slow chopper (Fermi-type) have also been made, in order to improve the statistics. We have, however, found some difficulty in using this chopper. This is because the trans- mission of epithermal neutrons gives a background with maxima and minima as a function of time-of-flight. One can do the measurements only in the minimum part of the background, i.e. , one can only cover a narrow energy region in each run. Furthermore, the speed of the rotor must be constant all over the measuring time - otherwise the chosen proper position for a measurement will be shifted towards the maximum part of the background, which, of course, will give a wrong value of the total neutron cross-section. The sample holder is made of stainless steel and can be put in- side a tube made of the same material. The heating is done electri- cally, by means of a coil around the tube. The arrangement - 4 - is such» that the temperature of the sample will be constant within - 10 C. The maximum temperature is about 900 C. 3. MEASUREMENTS AND RESULTS The measurements were carried out in the energy range from 0. 0045 eV to 0. 028 eV. Calibration of the energy scale was made by using the (110) Bragg edge in the cross-section for iron. The neutron energy for this edge is 0. 00499 eV. All three of the materials were measured at 20 C. ThO2 was also measured at 750 C. The experimental results have not been corrected for the reso- lution of the chopper. This resolution has the half-width A E = 0. 294 E \|E eV and is approximately shown as a triangle on the diagrams. 3. 1 Uranium A cast piece of U metal, with the thickness 25 mm and the den- sity 18. 7 g/cm , was used for the transmission measurements. A microphotography of one of the surfaces of the sample showed a grain size varying from about 5 fi- to 300 JUL. So far the cross-section has been measured only at room tem- perature. Preliminary tests at 900 C at the metallurgical laboratory with uranium-metal wrapped in zircaloy and placed in a steel con- tainer, were not successful. Renewed tests are going on and maybe later one can measure the total neutron cross-section of uranium at high temperature to study the effects of the phase transformation from a to (3 and from [3 to v . The results for the cross-section measurements at room tem- perature are given in fig. 2. The experimental points have been joined by a curve drawn by eye. The errors indicated are statistical. Other errors are small (in a rough estimation - 1 %) except for possible effects of the resolution. Below, the experimental results will be compared with some calculated results. It is known that the crystal structure of tf-uranium is orthorohom bic with the lattice constants ' : - 5 - a = 2. 852 A b '=5. 865 A and c = 4. 945 A (see fig. la). There are 4 atoms per unit cell. These four atoms have the following coordinates: (0,y, 1/4) ; (0,7.3/4) ; (1/2, 1/2+y, 1/4) ; (1/2, 1/2-y, 3/4). Bragg reflections appear only for h + k = even and the structure factor reduces to two simple expressions: £ = odd F = 4 & sin 2 IT yk i = even F = 4 aTT cos 2 w yk The parameter y is given as 0. 105 - 0.005 in [2] . We have used this value in the present calculation- The scattering amplitude "12 aTJ was chosen as 0.85 " 10 cm. All possible planes (h, k, l) of reflections below 0.02 eV are listed in Table I. Also listed are the heights of the Bragg edges per atom after correction for the Debye- Waller factor. The Debye-temperature was chosen as 144 K. This value was obtained from the discussion in [4] , page 387, using the resistivity in uranium at room temperature equal to 30 10 ohm cm. One can compare the heights of Bragg edges in fig. 2 with the calculated values in Table I. Take,for instance, the measured edge around 0.0134 eV. It is about 1. 5 b in height and corresponds to the sum of the edges for indices (221), (004) and (202). According to Table I the calculated height is 1.504 b. For other edges the agreement is also reasonable - the statistics does not allow any more precise statement. In a more justified comparison between experiment and theory one must also take into account the effect of the resolution. From the measurements of or. (E) in fig. 2 one can make an estimate of the parameter y . The planes of reflections with Miller indices (130) and (132) give a very low height of the edges. This means that cos 6 IT y must be close to zero. If cos 6 7T yis exactly zero one gets y = 0. 083. The edges for Miller indices (220) and (024) + (222) are also low according to fig. 2 and the structure factor must be close to zero. If cos 4 ft y = 0 , one gets y = 0. 125. We have not tried to make a - 6 - better estimate of y from our measurements. However, it it likely that the correct value must be somewhere between 0.083 and 0.125. [2] gives y = 0.105 - 0.005. 3. 2 Uranium oxide A sintered piece of micro-crystalline UO_ (grain size < 10 \x), 3 of thickness 34 mm and of density 10.1 g/cra » was used for the total neutron cross-section measurements. Fig. 3 gives the total neutron cross-section per molecule of UO~ measured at 20 C. The measurement at 750 C was not successful, because after the measuring time when we examined the sample, we found that it had been transformed into fine powder, making the effective sample thickness uncertain. The calculated positions of the Bragg edges are given in Table II. These calculations were made for the crystal structure of UO9 at 20 C, 5 which is of GaF^-type as shown in fig. 1 b. The lattice constant is a = 5. 4682 A. o There are three types of reflections: U + 2 O, U or U-2 O. The plus-sign means that the structure factor contains (aTT + 2 a,J where the a:s are scattering amplitudes. One can see from fig. 3 that the (U + 2 O) reflections for (220) and (422) are strong. This is a con- sequence of the fact that a,, and a~ have the same sign. 3. 3 Thorium oxide The sample consisted of ceramic microcrystalline thorium oxide disks with the thickness 22. 5 mm and the density 8. 71 g/cm . Fig. 4 gives the total neutron cross-section per molecule of ThO2. The solid curve gives <? (E) at 20°C> and the dotted curve gives er (E) at 750 C. The thermal expansion of the sample was taken into account in the determination of the total neutron cross- section at 750 C. As is evident from fig.
Load more

Recommended publications
  • Neutron-Induced Fission Cross Section of 240,242Pu up to En = 3 Mev
    Neutron-induced fission cross section of 240;242Pu Paula Salvador-Castineira~ Supervisors: Dr. Franz-Josef Hambsch Dr. Carme Pretel Doctoral dissertation PhD in Nuclear Engineering and Ionizing Radiation Barcelona, September 2014 Curs acadèmic: Acta de qualificació de tesi doctoral Nom i cognoms Programa de doctorat Unitat estructural responsable del programa Resolució del Tribunal Reunit el Tribunal designat a l'efecte, el doctorand / la doctoranda exposa el tema de la seva tesi doctoral titulada __________________________________________________________________________________________ _________________________________________________________________________________________. Acabada la lectura i després de donar resposta a les qüestions formulades pels membres titulars del tribunal, aquest atorga la qualificació: NO APTE APROVAT NOTABLE EXCEL·LENT (Nom, cognoms i signatura) (Nom, cognoms i signatura) President/a Secretari/ària (Nom, cognoms i signatura) (Nom, cognoms i signatura) (Nom, cognoms i signatura) Vocal Vocal Vocal ______________________, _______ d'/de __________________ de _______________ El resultat de l’escrutini dels vots emesos pels membres titulars del tribunal, efectuat per l’Escola de Doctorat, a instància de la Comissió de Doctorat de la UPC, atorga la MENCIÓ CUM LAUDE: SÍ NO (Nom, cognoms i signatura) (Nom, cognoms i signatura) President de la Comissió Permanent de l’Escola de Doctorat Secretària de la Comissió Permanent de l’Escola de Doctorat Barcelona, _______ d'/de ____________________ de _________ Universitat Politecnica`
    [Show full text]
  • Neutron Capture Cross Sections of Cadmium Isotopes
    Neutron Capture Cross Sections of Cadmium Isotopes By Allison Gicking A thesis submitted to Oregon State University In partial fulfillment of the requirements for the degree of Bachelor of Science Presented June 8, 2011 Commencement June 17, 2012 Abstract The neutron capture cross sections of 106Cd, 108Cd, 110Cd, 112Cd, 114Cd and 116Cd were determined in the present project. Four different OSU TRIGA reactor facilities were used to produce redundancy in the results and to measure the thermal cross section and resonance integral separately. When the present values were compared with previously measured values, the differences were mostly due to the kind of detector used or whether or not the samples were natural cadmium. Some of the isotopes did not have any previously measured values, and in that case, new information about the cross sections of those cadmium isotopes has been provided. Table of Contents I. Introduction………………………………………………………………….…….…1 II. Theory………………………………………………………………………...…...…3 1. Neutron Capture…………………………………………………….….……3 2. Resonance Integral vs. Effective Thermal Cross Section…………...………5 3. Derivation of the Activity Equations…………………………………....…..8 III. Methods………………………………………………………….................…...…...12 1. Irradiation of the Samples………………………………………….….....…12 2. Sample Preparation and Parameters………………..………...………..……16 3. Efficiency Calibration of Detectors…………………………..………....…..18 4. Data Analysis…………………………………...…….………………...…..19 5. Absorption by 113Cd……………………………………...……...….………20 IV. Results………………………………………………….……………..……….…….22
    [Show full text]
  • EVALUATION of NEUTRON CROSS SECTIONS for Cm-242, -243, -244
    XA0100537 -67- UDC 539.172 EVALUATION OF NEUTRON CROSS SECTIONS FOR Cm-242, -243, -244 A.I. Blokhin, A.S. Badikov, A.V. Ignatyuk, V.P. Lunev, V.N. Manokhin, G. Ya. Tertychny, K.I. Zolotarev Institute of Physics and Power Engineering, Obninsk, Russia EVALUATION OF NEUTRON CROSS SECTIONS FOR Cm-242, -243, -244. The work is devoted to the analysis of available experimental and evaluated data on the neutron cross sections for Cm-242, Cm-243, Cm-244. A comparison of experimental data with the results of theoretical calculations and the evaluations of the most important cross sections were performed. As a result the new version of complete files of evaluated neutron cross sections for Cm-242, Cm-243, Cm- 244 were performed. These files were included into the BROND-3 library the formations of which is under development in Russian Nuclear Data Center. For curium isotopes there are considerably less experimental data than for americium isotopes. The measurements of the total and radiative capture cross sections are restricted to the neutron resonance region and only the fission cross sections were measured in the fast neutron energy region. That is why all the neutron cross section evaluations are mainly based on the analysis of the available measured fission cross sections and on the statistical calculations of other cross sections. For Cm-245 and Cm-246 the new experimental fission cross sections, obtained in the framework of the Project [18] agree good enough with the available experimental data and the new cross section evaluations made by Minsk's group in 1996 [1, 2].
    [Show full text]
  • Testing of Evaluated Transactinium Isotope Neutron Data and Remaining Data Requirements
    Testing of Evaluated Transactinium Isotope Neutron Data and Remaining Data Requirements H. Kiisters Nuclear Research Center Karlsruhe Institute of Neutron Physics and Nuclear Engineering 1. Introduction The first international meeting on transactinium isotope nuclear data, held in Karlsruhe in 1975 /l/, mainly dealt with neutron cross-sections and other nuclear properties as e.g. decay constants of minor actinide isotopes, abbreviated in this paper to MINACs. For the plutonium and the thorium fuel cycle, the MINAC isotopes are 230Th up to 244C, with the exception of the main nuclei 232Th, 233U, 235U, 23aU, 23gPu, 240Pu and 241Pu (sometimes the higher Pu isotopes are incorrectly counted as MINACs; for special interests the curium isotopes beyond mass number 244 are also included in the MINAC list). Minor actinide isotopes are understood to be of "minor importance" in thermal and fast reactor design. This minor importance is regarded with respect to the influence of these nuclei on the reactivity balance or the neutron spectrum of a nuclear plant. However, the MINACs can be of prime importance in the out-of-pile stages of the nuclear fuel cycle, especially in determini% the decay heat and the neutron as well as alpha, beta and gamma radiation of spent nuclear fuel after discharge from the reactor. These aspects are essential for designing safe transport casks and inter- mediate storage facilities, reprocessing units and waste disposal sites. The intensive discussion on the nuclear data aspects of MINACs originated from the predicted expansion of nuclear energy after the first oil crisis in 1973. Reprocessing units of sizes up to 1500 to/yr throughput were dis- cussed, recycling of Pu in thermal reactors was, and in some countries is considered as a serious strategy besides the introduction of Pu into fast ~breeder reactors; also U-recycling came into the discussion.
    [Show full text]
  • AN34 Application Note Experiment 17 Neutron Activation Analysis
    ® ORTEC AN34 Experiment 17 Neutron Activation Analysis (Slow Neutrons) Equipment Needed from ORTEC colorimetric, spectrographic, or mass spectroscopy, its sensitivity is usually shown to be better by a factor of 10 than that of other • 113 Scintillation Preamplifier methods. Activation analysis is used extensively in such fields as • 266 Photomultiplier Tube Base geology, medicine, agriculture, electronics, metallurgy, • 4006 or 4001A/4002D Bin and Power Supply criminology, and the petroleum industry. • 556 High Voltage Power Supply • 575A Amplifier The Neutron Source • 905-3 2-in. x 2-in. or 905-4 3-in. x 3-in. NaI(Tl) Detector and PM This experiment is described using 1 Ci of Am-Be for the Tube neutron source, with the source located in the center of a • Easy-MCA 2k System including a USB cable, a suitable PC paraffin howitzer. The samples are irradiated at a point ~4 cm and MAESTRO-32 software (other ORTEC MCAs may be from the source by the neutrons whose energies have been substituted) moderated by the paraffin between that point and the source. • Coaxial Cables and Adapters: Any of the commonly found isotopic neutron sources can be • One C-24-1/2 RG-62A/U 93-Ω coaxial cable with BNC plugs used for this experiment. on both ends, 15-cm (1/2-ft) length. Neutron Activation Equations Ω • One C-24-12 RG-62A/U 93- coaxial cable with BNC plugs Assume that the sample has been activated in the howitzer. At on both ends, 3.7-m (12-ft) length. the instant when the activation has been terminated, (tc = 0), the • Two C-24-4 RG-62A/U 93-Ω coaxial cables with BNC plugs activity of the sample is given by the following expression: on both ends, 1.2-m (4-ft) length.
    [Show full text]
  • Neutron Cross Section Evaluation of U-238
    FIESTA2017 FIssion ExperimentS and Theoretical Advances Neutron Cross Section Evaluation of U-238 Hyeong Il Kim Nuclear Data Center Korea Atomic Energy Research Institute 2017. 9. 18 Table of Contents 1 Introduction 2 Nuclear Data Evaluation 3 Results 4 Summary Introduction Overview Introduction Nuclear Data Evaluation Analyzing the measured physical quanties + Combing them with theoretical predictions => Extract the true values of such quanties DataBase ENDF Library (Compact format) Processed to Pointwised or Groupwised Libraries Application Inputs for various simulation codes (MCNP, Geant4, PHITS, DRAGON, DANTSYS, DORT ··· ) FIESTA2017, Eldorado Hotel, Santa Fe, NM H. I. Kim 1 Introduction Overview Nuclear data activities An example of nuclear data eval. for 235U Applications FIESTA2017, Eldorado Hotel, Santa Fe, NM H. I. Kim 2 Introduction Overview Uranium Abundances of natural uranium 234U: 0.0054 % 235U: 0.7204 % 238U: 99.2742 % U-238 Fuel of nuclear reactor LWR: 95 ∼ 97 %, HWR: 98 ∼ 99 % Well evaluated but Continuoulsy updated Current version: ENDF/B-VII.1, JENDL-4.0, JEFF-3.2,CENDL-3.1,RUSFOND-2010,... Preliminary: ENDF/B-VIII-b4, JEFF33T4 FIESTA2017, Eldorado Hotel, Santa Fe, NM H. I. Kim 3 Nuclear Data Evaluation Cross section Cross sections for U-238 FIESTA2017, Eldorado Hotel, Santa Fe, NM H. I. Kim 4 Nuclear Data Evaluation Cross section Cross Sections Cross Sections Cross Section: function of the kinetic energy of the particle a ZZ 2 d σ(Ea; Eb; Ω) σ(Ea) = dEbdΩ dEbdΩ Differential Cross Section: Distributions of an emitted particle for anlge or energy dσ(Ea; Eb) dσ(Ea; Ω) dEb dΩ Double-Differential Cross Section (DDX): Distributions of an emitted particle for anlge and energy 2 d σ(Ea; Eb; Ω) dEbdΩ FIESTA2017, Eldorado Hotel, Santa Fe, NM H.
    [Show full text]
  • Lecture 5 — Wave and Particle Beams
    Lecture 5 — Wave and particle beams. 1 What can we learn from scattering experiments • The crystal structure, i.e., the position of the atoms in the crystal averaged over a large number of unit cells and over time. This information is extracted from Bragg diffraction. • The deviation from perfect periodicity. All real crystals have a finite size and all atoms are subject to thermal motion (at zero temperature, to zero-point motion). The general con- sequence of these deviations from perfect periodicity is that the scattering will no longer occur exactly at the RL points (δ functions), but will be “spread out”. Finite-size effects and fluctuations of the lattice parameters produce peak broadening without altering the integrated cross section (amount of “scattering power”) of the Bragg peaks. Fluctuation in the atomic positions (e.g., due to thermal motion) or in the scattering amplitude of the individual atomic sites (e.g., due to substitutions of one atomic species with another), give rise to a selective reduction of the intensity of certain Bragg peaks by the so-called Debye- Waller factor, and to the appearance of intensity elsewhere in reciprocal space (diffuse scattering). • The case of liquids and glasses. Here, crystalline order is absent, and so are Bragg diffraction peaks, so that all the scattering is “diffuse”. Nonetheless, scattering of X-rays and neutrons from liquids and glasses is exploited to extract radial distribution functions — in essence, the probability of finding a certain atomic species at a given distance from another species. • The magnetic structure. Neutron possess a dipole moment and are strongly affected by the presence of internal magnetic fields in the crystals, generated by the magnetic moments of unpaired electrons.
    [Show full text]
  • Moderator Design for Accelerator Based Neutron Radiography and Tomography Systems
    Moderator Design For Accelerator Based Neutron Radiography and Tomography Systems by Donald B. Puffer Submitted to the Department of Nuclear Engineering in partial ful- fillment of the requirements for the degree of Master of Science in Nuclear Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY August 1994 © Massachusetts Institute of Technology, 1994. All Rights Reserved. A uthor ..................................... .................... .................................................. Department of Nuclear Engineering August 19, 1994 Certified by •., - 7/7' ....... " PiiaRsr Sciei < o Dr. Richard Lanza SPrincipal Research Scie Department of Nuclear Engineering Thesis Supervisor R ead by .... ...... .... .......... .... .................................................................. Dr. Jacquelyn Yanch / Professor of Nuclear Engineering Thesis Reader A ccepted by ............................... ........... ..... ............................................... Dr. Allen Henry rs., -Chairman, Committee on Graduate Students Department of Nuclear Engineering o V 16 1994 Moderator Design For Accelerator Based Neutron Radiography and Tomography Systems by Donald B. Puffer Submitted to the Department of Nuclear Engineering on August 19, 1994, in partial fulfillment of the requirements for the degree of Master of Science in Nuclear Engineering Abstract MIT is in the initial phase of developing a small accelerator based neutron imaging system. The system includes a radiofrequency quadrupole (RFQ) accelerator--producing neutrons by the
    [Show full text]
  • 3.22 Measurement of Neutron Spallation Cross Sections
    JAERI-Conf 96-008 3.22 Measurement of Neutron Spallation Cross Sections E.Kim,T.Nakamura,A.Konno(CYRIC,Tohoku Univ.),M.Imamura,N.Nakao T.Shibata(INS,Univ.of Tokyo),Y.Uwamino,N.Nakanishi(Institute of Physical and Chemical Research),Su.Tanaka,H.Nakashiman, Sh.Tanaka,(JAERI) Neutron spallation cross sections of l2C(n,2n)"C and 2O9Bi(n,xn)2IOxBi were measured in the quasi-monoencrgetic p-Li neutron fileds in the energy range of 20McV to 210MeV which have been established at four AVF cyclotron facilities of 1)INS of Univ. of Tokyo, 2)TIARA of JAERI, 3)CYRIC of Tohoku Univ., and 4)RIKEN. Our experimental data were compared with other experimental data and the ENDF/B-VI high energy file data. 1. Introduction At present, a demand for neutron reaction data is world-wide increasing from the viewpoints of intense neutron source of material study, induced radioactivity and shielding design of high energy accelerators. Nevertheless, neutron reaction data in the energy range above 20MeV are very poor and no evaluated data file exists at present mainly due to very limited number of facilities having quasi-monoenergetic neutron fields. In this study, we measured the neutron spallation cross sections of I2C, 27A1,59Co and 209Bi which has been and will be used for high energy neutron spectrometry, by using quasi-monoenergetic p-Li reutrons in the energy range of 20MeV to 210MeV. 2.Experiment The experiments were performed at four cyclotron facilities of 1 institute for Nuclear Study ( INS ),University of Tokyo for 20 to 40 McV, 2)Cyclotron and Radioisotopc Center (CYRIC),Tohoku University for 20 to 40 MeV, 3)Takasaki Research Establishment, Japan Atomic Energy Reserch Institute (TIARA) for 40 to 90MeV and 4)Institute of Physical and Chemical Research (RIKEN) for 80 to 210MeV.
    [Show full text]
  • Fast Neutron Cross Sections of 2L*°Pu; Measured Results and a Comparison
    Fast Neutron Cross Sections of 2l*°Pu; Measured Results and a Comparison with an Evaluated File À. B. Smith, P. P. Lambropoulos and J. F. Whalen Argonne National Laboratory Argonne, Illinois Abstract Fast neutron total cross sections and elastic- and inelaetic-scatter- ing cross sections of 2**°Pu are reported. The total cross sections are measured from neutron energies of 0.1 to 1.5 MeV in increments of *»* 25 keV. The elastic-scattering cross sections are measured at ^ 50 keV intervals from incident neutron energies of 0.3 to 1.5 MeV. The inelastic neutron excitation cross sections of states at 4 2 + 5 , 140 + 10, 300 + 2 0 , 600 + 20 and 900 + 50 keV are measured. The experimental results are discussed in the context of the optical, compound-nucleus and direct-reaction nuclear models including the effects of resonance width fluctuations and the fission process. The measured results are critically compared with the corresponding quantities in the evaluated nuclear data file ENDF/2. I. INTRODUCTORY REMARK The isotope 2t*°Pu is a major constituent of many fast-breeding reactors wherein the plutonium fuel may consist of £ 20 percent 2lf0Pu.^ Therefore fast neutron interactions with this isotope are a considera­ tion in the neutronic design of these systems. Despite this applied importance the experimental microscopic fast neutron cross sections of 2*°Pu are relatively unknown and a number of requests for measured in- 2 ' formation are outstanding. Major reliance continues to be placed upon evaluated data sets based largely on nuclear-model estimates. The fission neutron cross section of 2tfl*Pu has been reasonably well 3 4 5 measured.
    [Show full text]
  • Nuclear Data Development at the European Spallation Source
    Nuclear data development at the European Spallation Source Jose Ignacio Marquez Damian a;∗, Douglas D. DiJulio a, and Günter Muhrer a, a Spallation Physics Group, European Spallation Source ERIC, Lund, Sweden Abstract. Transport calculations for neutronic design require accurate nuclear data and validated computational tools. In the Spallation Physics Group, at the European Spallation Source, we perform shielding and neutron beam calculations to help the deployment of the instrument suite for the current high brilliance (top) moderator, as well for the design of the high intensity bottom moderator, currently under study for the facility. This work includes providing the best available nuclear data in addition to improving models and tools when necessary. In this paper we present the status of these activities, which include a set of thermal scattering kernels for moderator, reflector, and structural materials, the development of new kernels for beryllium considering crystallite size effects, nanodiamonds, liquid hydrogen and deuterium based on path integral molecular dynamics, and the use of the software package NCrystal to assist the development of nuclear data in the framework of the new HighNESS project. Keywords: thermal scattering, neutron, nuclear data libraries 1. Introduction Neutronic calculations for the simulation and development of moderators and reflectors at spallation neutron sources, such as the European Spallation Source (ESS) [1], currently under construction in Lund, Sweden, require accurate models for the interaction of thermal and cold neutrons with matter in order to get the best possible estimates for the performance of the facility. For this reason, we have launched several activities at the ESS to produce updated and revised libraries for Monte-Carlo simulations.
    [Show full text]
  • Neutron Total Cross Section Measurements of Gold and Tantalum at the Nelbe Photoneutron Source
    Neutron total cross section measurements of gold and tantalum at the nELBE photoneutron source Roland Hannaske*, Zoltan Elekes, Roland Beyer, Arnd Junghans1, Daniel Bemmerer, Evert Birgersson2, Anna Ferrari, Eckart Grosse*, Mathias Kempe*, Toni Kögler*, Michele Marta3, Ralph Massarczyk*, Andrija Matic4, Georg Schramm*, Ronald Schwengner, and Andreas Wagner Helmholtz-Zentrum Dresden-Rossendorf Bautzner Landstr. 400, 01328 Dresden, Germany Abstract Neutron total cross sections of 197Au and natTa have been measured at the nELBE photoneutron source in the energy range from 0.1 – 10 MeV with a statistical uncertainty of up to 2 % and a total systematic uncertainty of 1 %. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5 ps) with a short flight path of 7 m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources. 1 Introduction Experimental neutron total cross sections as a function of neutron energy are a fundamental data set for the evaluation of nuclear data libraries. With increasing neutron energy the compound nucleus resonances cannot be resolved anymore and will start to overlap. In the energy range of fast neutrons, which is especially important for innovative nuclear applications, like accelerator driven systems for the transmutation of nuclear waste, the neutron total cross section can be described by optical model calculations (e.g. [1, 2]) where the range below 5 MeV shows a large sensitivity on the optical model parameters. The neutron total cross section of 197Au in the energy range from 5 – 200 keV is an item in the OECD NEA Nuclear Data High Priority Request list as 197Au(n,) is an activation standard in dosimetric applications [3].
    [Show full text]