DOCSLIB.ORG

An Improved Slow Neutron Spectrometer at the Research Reactor-R1

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Improved Slow Neutron Spectrometer at the Research Reactor-R1 EG9601747 AN IMPROVED SLOW NEUTRON SPECTROMETER AT THE RESEARCH REACTOR-R1 M.A. ABU EL-ELA Reactor and Neutron Physics Department, Nuclear Research Center. AEA. Cairo. Egypt. ABSTRACT An improved slow neutron selector has been aligned at channel number 6 of the nuclear research Reactor-Rl-lnshas. The flight path is 3.75 meter. The collimator-rotor-collimator system has the dimensions 0.3 x 2.5 x 70 cm3 with the rotor diameter 16 cm and 3 slits of 0.3 x 2.5 cm2 cross section. The rotor rotation rate varies between 600 r.p.m and 3600 r.p.m. The counting system has one of the best modern high electronic advanced technology time analyzer with minimum Dwell time 2 jisec, 8192 channels and a Double detector inputs of TTL and NEG NIM standard pulses. The analyzer external Triggering signals are of TTL standard type. A special design 3He detector for Time of flight spectrometry has been used in the SNS. The reactor bare thermal neutron spectrum has been successfully measured. INTRODUCTION Neutron spectrometers can be arranged into 4 generations, since the discovery of the neutron in 1932. The first 2 generations are a twin characterized by the dual property of the neutron. 12 k The first generation of the twin consider the neutron as a particle, in this case, mechanical treatment could be done, through a mechanical chopper. These mechanical choppers^ " ' can be mainly classified into, fast 3 5 4 6 17 I9 2 neutron choppers^ ' ) and slow neutron choppers^ ' " « ' °)$ Both are jointly arranged by 3 rotor parameters; 1 -neutron scattering rotors; 2-neutron absorbing rotors; 3- shape of slit inside the rotor, (straight, curved, cigar, barrel, helical). These choppers started by one slit rotor, followed by multi- slits rotor ^ followed by multi-rotors spectrometers^ >5'2°). The second generation of the twin consider the neutron as a wave, in this case, wave reflection and diffraction treatment could be used, through a single crystal. This generation started by a (straight) single crystal*18^, followed by 2 single crystals, the first crystal as neutron monochromator and the second crystal as neutron analyzed \ (Neutron Triple axes spectrometer). The third generation is a combination between the first generation and the second generation, The fourth generation considers the neutron spin. The high advanced technology helped much more in solving many problems, to provide the neutron spin spectrometers and the associated neutron guide tubes. The present spectrometer is one of the simplest slow neutron mechanical choppers, and high advanced technology electronics. The mechanical part is the same as was done in 1974' \ The electronic system is completely different from the old one, between the use of valve tubes and the use of integrated circuits ICs, besides, avoiding the use of mechanical tachogenerator (amplidyne) to the use of electronic tachogenerator, that prevents any additional mechanical load on the motor of the rotor. The use of NEG N1M logic pulses instead of TTL pulses introduces a better resolution for the counting system. Special time of flight (TOF) He detector with diameter half of the BF3 old one , and better resolution is used. The time multichannel analyzer provides a dwell time of 2|isec, compared with 16 u.sec in the old one with the ratio 1:8 and 10 jisec in the most recent 125 neutron spectrometer in the reactor and neutron physics department of the necular research center^, with the ratio 1:5. This facility is very important, specially in the case of neutron elastic and inelastic scattering, where the need to distinguish between closed peaks is required. The use of IC's in building the system had helped in decreasing the ratio between the noise level and the effective values. The spectrometer can be used in the neutron wavelength range from 0.5 A to 6 A. This range can be extended to 10 A by increasing the power of the reactor, and using a higher vacuum flight path tube. THE EXPERIMENTAL PROCEDURES 1- An inpile collimator had been designed from Pb with dimensions 25x2.5x0.4 cm3, to decrease the spectrometer background and keep it safe. 2- The neutron beam center had been determined, by using dual scanning, in the horizontal position and the vertical one, at flight path lengths 3.75, 5, 6, 6.5 meters. 3- The spectrometer has a collimator-rotor-collimator system. In order to keep very carefully the intensity at maximum, the following scheme 123 (Rotor-lst collimator-2nd collimator) had been used: v —~ ••* •••-•i- ' Neutron 1 ? | y 1 i | a beam Istcollimator Rotor 2nd collimator 3.1- The rotor (1) had been adjusted to give the maximum counting rate, by using the orientation screws at the base of mechanical part. 3.2- The collimator (2) had been adjusted using the same scheme and the orientation screws at the base of the collimator. 3.3- The collimator (3) had been adjusted using the same scheme as in (2). 126 4- Start triggering signals: 4.1 Two magnetic cells had been designed and built in aluminum disk of the same diameter of the rotor. The carrier aluminum disk (of magnetic cells) had been fixed at the same shaft of the motor and the rotor, with the magnetic cells perpendicular to the slits in the rotor. 4.2- 10 magnetic pick up heads had been tested, to select the best, the selected magnetic pick-up head had been fixed in the proper position, as close as possible to the magnetic cells during its rotation point by point with the rotor, to produce the start signals, that trigger the multichannel time analyzer. 4.3- An adjustable system had been designed to absorb the motor vibration, and keep it stable at the same center line with rotor and the carrier disk of the magnetic cells. 5- The safety of the spectrometer: 5.1- The collimator-rotor-collimator mechanical part of the spectrometer (the hot area) had been surrounded by 1 mm cadmium, slow neutron high absorbing material; about 80 cm high boron paraffin mixture blocks, 5 cm of high boron condensed polyethylene blocks, and 5 mm of lead. 5.2- The path of the neutron beam from the reactor to the hot area of the collimator-rotor-collimator is rounded by 20cm boric acid, 2cm iron, and 5mm lead. 5.3- The flight path had been rounded by 10cm boric acid, 10cm paraffin, 10cm boric acid, and 5mm lead. 5.4- The detector area had been completely rounded by 10cm boric acid, 10cm paraffin, 10cm boric acid and 5mm lead. 5.5- At the end of the spectrometer a beam cature had been used to stop any leaked y-rays and fast neutrons. 6- Supply and counting system : Since the control system should be far from the reactor hall, the needed supply cables to the spectrometer, and the data cables had been 127 extended for 70 meters from the reactor hall to the control room, through special tunnels. 7- Special technique had been used to get the start triggering pulses before the rotor opens the slits, to create the neutron bursts, with a suitable lagging time. This technique is useful to determine the following: (1) The zero time channel of the measured neutron spectra. (2) The background of the measured neutron spectra, neutron burst by neutron burst. This means that there is no need to get the associated background in a separate measurement, and save the reactor operation time. RESULTS AND DISCUSSION 1- The spectrometer layout can be seen in Fig. (1). 2- The used shielding materials in building the spectrometer had provided a safe spectrometer. This result has been assured by the official radiation survey around the spectrometer of the Protection Department. The radiation level is lower than the international base level. It means that the spectrometer is completely protected from the other experiments in the reactor hall and vice versa. 3- The reactor neutron beam and the spectrometer: 3.1- The reactor neutron beam spectrum, as a neutron source, has a very wide range, starting from fast neutrons (fission process in the core) and ending by cold neutrons. 3.2- The present spectrometer is a slow neutron spectrometer type. So, there is a problem, how can you use the thermal and cold neutrons as a neutron source to the spectrometer, in the presence of associated y-rays and fast neutrons? 3.3- The spectrometer is connected with the reactor neutron beam in two points. The first point is the rotor, and the second is the detector. The rotor material is a high scatterer to the thermal and cold neutrons, so it prevents the passage of these neutrons, and controls the passage of these 128 3456 789 10 11 12 13 | ro 14 15 16 17 18 19 Fig.(l) Spectrometer Layout . Inpile shield, 2- Inpile collimator, 3- Lead. 4- Outpile collimator, 5- Lead, 6- Iron , 7- Boric acid, 8- Cadmium, 9- Borated paraffin, 10- Lead, 11- Shielding wall, 12- Detector shield, 13- Detector, 14- fan, 15- Motor, 16-Rotor, 17- Magnetic phono preamplifier, 18- Borated polyethylene blocks, 19- Beam cature neutrons only through its slits. So, the created neutron bursts through the slits of the rotor contain all the reactor spectrum contents, y-rays and fast neutrons, slow and cold neutrons, while the passing spectrum, when the slits are closed, contains only y-rays and fast neutrons, it will be treated as background as follows later. The second point is the detector, that should be selected very carefully as follows : 1.1- The detector material should have a very high absorption cross section to the thermal and cold neutrons and give interaction products to be registered.
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]