scholarly journals Towards the experimental validation of a small Time-Projection-Chamber for the quasi-absolute measurement of the fission cross section

2021 ◽  
Vol 253 ◽  
pp. 11013
Author(s):  
Carole Chatel ◽  
Ludovic Mathieu ◽  
Mourad Aïche ◽  
Maria Diakaki ◽  
Gilles Noguere ◽  
...  
Keyword(s):  
Neutron Flux ◽  
Cross Section ◽  
Neutron Energy ◽  
Cross Sections ◽  
Detection Efficiency ◽  
Silicon Detector ◽  
Fission Cross Section ◽  
Absolute Measurement ◽  
Small Time ◽  
Flux Measurements

To accurately measure neutron-induced fission cross sections, to characterize neutron-beam lines or to make dosimetric investigations, it is necessary to have high accuracy measurements of neutron fluence. It is possible to perform independent and precise neutron flux measurements with respect to the 1H(n,n)p elastic scattering cross section. The use of a silicon detector is recommended from 1 to 70 MeV neutron energy. However, it has been observed that a high electrons background forbids its use below 1 MeV. Hence, a new gaseous proton-recoil telescope is developed and characterized to overcome this limit. It should provide quasi-absolute neutron flux measurements with an accuracy around 3% and is not sensible to gamma and electrons background. It consists in two ionization chambers read by a segmented micromegas technology detection plane. The gas pressure inside is adjustable to the proton range in the detector and therefore to the neutron energy. This detector is described in details below and the newest results of its characterization are presented. A special attention is paid to detection efficiency measurements.

scholarly journals Measurement of the 235 U(n,f) cross section at n_TOF from thermal to 170 keV

2020 ◽  
Vol 50 ◽  
pp. 2060011
Author(s):  
Simone Amaducci ◽  
S. Amaducci ◽  
O. Aberle ◽  
J. Andrzejewski ◽  
L. Audouin ◽  
...  
Keyword(s):  
Neutron Flux ◽  
Cross Section ◽  
Nuclear Physics ◽  
Detection Efficiency ◽  
Neutron Cross Section ◽  
Fission Cross Section ◽  
Ratio Method ◽  
Recent Experimental Data ◽  
Silicon Detectors ◽  
Flux Measurements

The [Formula: see text]U(n,f) cross section plays a key role for nuclear physics due to its widespread use as a standard reference for neutron cross section measurements and for neutron flux measurements. Recent experimental data of the fission cross section have suggested the presence of discrepancies around 6–8% with respect to the most used libraries, precisely in the range between 10 keV and 30 keV. In order to shed light on this disagreement, an accurate measurement of the [Formula: see text]U(n,f) fission cross section has been performed at n_TOF facility @CERN, using the standard reactions 6Li(n,t) and [Formula: see text]B(n,[Formula: see text] as reference. A custom experimental setup based on a stack of silicon detectors sandwiched between pairs of [Formula: see text]U, 6Li and [Formula: see text]B targets, has been installed along the neutron beam line to intercept the same neutron flux, allowing the detection of the fission fragments and the products of the reference reactions at the same time. Such a technique allows calculation of the cross section via the “ratio method”, by normalizing the [Formula: see text]U(n,f) reaction yields with respect to the reference reactions and to the recommended data in the IAEA libraries; in particular, the integral between 7.8 and 11 eV has been chosen. Accurate Monte Carlo simulations have allowed evaluation of the neutron absorption in the different layers, as well as the detection efficiency of each detector. The data are in excellent agreement with the standard values and highlight the overestimation of the [Formula: see text]U(n,f) cross section between 9 and 18 keV in the most recent libraries.

scholarly journals Development of a Gaseous Proton-Recoil Detector for neutron flux measurements between 0.2 and 2 MeV neutron energy

2019 ◽  
Vol 211 ◽  
pp. 03010
Author(s):  
P. Marini ◽  
L. Mathieu ◽  
M. Aïche ◽  
T. Chiron ◽  
P. Hellmuth ◽  
...  
Keyword(s):  
Neutron Flux ◽  
Cross Section ◽  
Neutron Energy ◽  
Elastic Cross Section ◽  
Proton Spectrum ◽  
Incident Neutron ◽  
High Background ◽  
Flux Measurements ◽  
Proton Recoil ◽  
Absolute Measurements

Absolute measurements of neutron fluence are an essential prerequisite of neutron-induced cross section measurements, dosimetric investigations and neutron beam lines characterisation. Independent and precise neutron flux measurements can be performed with respect to the H(n,p) elastic cross section. However, the use of silicon proton recoil detectors is not straightforward below incident neutron energy of 1 MeV, due to a high background in the detected proton spectrum. A new gaseous proton-recoil detector has been designed to answer the challenge. The detector is described in details and results of the commissioning tests are presented.

Measurements of the cross-section of 111Cd(n,n′)111mCd reaction for 241Am/Be neutrons

2021 ◽  
pp. 2150084
Author(s):  
G. S. M. Ahmed ◽  
M. Tohamy ◽  
P. Bühler ◽  
M. N. H. Comsan
Keyword(s):  
Cross Section ◽  
Neutron Energy ◽  
Cross Sections ◽  
Detection Efficiency ◽  
Neutron Fluence ◽  
Reaction Products ◽  
The Cross ◽  
Cadmium Target ◽  
Average Neutron ◽  
Average Neutron Energy

The cross-section of the [Formula: see text] reaction was measured with [Formula: see text] neutrons using a natural cadmium target [Formula: see text]. The neutron fluence and mean neutron energy of the source were determined using the ISO 8529-1 neutron spectrum and the known cross-sections of the monitor reaction [Formula: see text]. In order to measure the poor [Formula: see text]-ray activity of the reaction products, an HPGe detector with 70% detection efficiency surrounded by an adequate graded shield was applied. The efficiency calculations for the detector were performed using standard point calibration sources and the EFFTRAN efficiency code. Using the measured values of the neutron flux and the induced [Formula: see text]-ray activity of [Formula: see text], the cross-section of the [Formula: see text] reaction at the average neutron energy of 4.05 MeV was found to be [Formula: see text] mb. An estimation of the contribution to the total cross-section by the accompanied reactions [Formula: see text] and [Formula: see text] was achieved and the related cross-sections were found to be 0.16 mb and 8.99 mb, respectively.

scholarly journals Uncertainty Analysis of WWER-1000 Core Macroscopic Cross Sections due to Spectral Effects

2020 ◽  
pp. 39-46
Author(s):  
О. Kukhotska ◽  
I. Ovdiienko ◽  
M. Ieremenko
Keyword(s):  
Energy Spectrum ◽  
Isotopic Composition ◽  
Uncertainty Analysis ◽  
Neutron Flux ◽  
Flux Density ◽  
Cross Section ◽  
Cross Sections ◽  
Fuel Burnup ◽  
Thermophysical Parameters ◽  
Neutron Flux Density

The paper presents the results of uncertainty analysis of WWER‑1000 core macroscopic cross sections due to spectral effects during WWER‑1000 fuel burnup and the analysis of cross section sensitivity from thermophysical parameters of the calculated cell, which affect energy spectrum of neutron flux density. The calculation of changes in the isotopic composition during burnup and the preparation of macroscopic cross sections used the developed HELIOS computer model [1] for TVSA, which is currently operated at most Ukrainian WWER‑1000 units. The GRS approach applying Software for Uncertainty and Sensitivity Analyses (SUSA) [2] was chosen to assess the uncertainty of the macroscopic cross sections due to spectral effects and analysis of cross section sensitivity from thermophysical parameters. The spectral effect on macroscopic cross sections was taken into account by calculating the fuel burnup for variational sets of thermophysical parameters (fuel temperature, coolant temperature and density, boric acid concentration) prepared in advance by the SUSA program, as a result of which fuel isotopic composition vectors were obtained. After that, neutronic constants for the reference state were developed for each of the sets of isotopic composition, which corresponded to a certain set of thermophysical parameters. At the next stage, the uncertainty of macroscopic cross sections of the interaction due to the spectral effects on the isotopic composition of the fuel was analyzed using SUSA 4, followed by the analysis of cross section sensitivity from thermophysical parameters of the calculated cell affecting energy spectrum of neutron flux density. In the future, the uncertainty of two-group macroscopic diffusion constants can be used to estimate the overall uncertainty of neutronic characteristics in large-grid core calculations, in particular, in the safety analysis.

scholarly journals Study of the 232Th(n,f) Cross section at NCSR ‘Demokritos’ using Micromegas Detectors

2020 ◽  
Vol 27 ◽  
pp. 106
Author(s):  
Sotirios Chasapoglou ◽  
A. Tsantiri ◽  
A. Kalamara ◽  
M. Kokkoris ◽  
V. Michalopoulou ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Nuclear Reactions ◽  
Detection Efficiency ◽  
High Energy ◽  
Tandem Accelerator ◽  
Line Detector ◽  
Accelerator Driven Systems ◽  
The Masses

The accurate knowledge of neutron-induced fission cross sections in actinides, is of great importance when it comes to the design of fast nuclear reactors, as well as accelerator driven systems. Specifically for the 232Th(n,f) case, the existing experimental datasets are quite discrepant in both the low and high energy MeV regions, thus leading to poor evaluations, a fact that in turn implies the need for more accurate measurements.In the present work, the total cross section of the 232Th(n,f) reaction has been measured relative to the 235U(n,f) and 238U(n,f) ones, at incident energies of 7.2, 8.4, 9.9 MeV and 14.8, 16.5, 17.8 MeV utilizing the 2H(d,n) and 3H(d,n) reactions respectively, which generally yield quasi-monoenergetic neutron beams. The experiments were performed at the 5.5 MV Tandem accelerator laboratory of N.C.S.R. “Demokritos”, using a Micromegas detector assembly and an ultra thin ThO2 target, especially prepared for fission measurements at n_ToF, CERN during its first phase of operations, using the painting technique. The masses of all actinide samples were determined via α-spectroscopy. The produced fission yields along with the results obtained from activation foils were studied in parallel, using both the NeusDesc [1] and MCNP5 [2] codes, taking into consideration competing nuclear reactions (e.g. deuteron break up), along with neutron elastic and inelastic scattering with the beam line, detector housing and experimental hall materials. Since the 232Th(n,f) reaction has a relatively low energy threshold and can thus be affected by parasitic neutrons originating from a variety of sources, the thorough characterization of the neutron flux impinging on the targets is a prerequisite for accurate cross-section measurements, especially in the absence of time-of-flight capabilities. Additional Monte-Carlo simulations were also performed coupling both GEF [3] and FLUKA [4] codes for the determination of the detection efficiency.

Cross section measurements for the reactions of fast neutrons with indium

1976 ◽  
Vol 54 (7) ◽  
pp. 757-765 ◽  
Author(s):  
D. C. Santry ◽  
J. P. Butler
Keyword(s):  
Neutron Flux ◽  
Cross Section ◽  
Neutron Spectrum ◽  
Cross Sections ◽  
Fission Neutron ◽  
Activation Method ◽  
Fast Neutrons ◽  
Fission Neutron Spectrum

Excitation curves for the reactions 115In(n,n′) 115Inm, 113In(n,n′)113Inm, and 115In(n,2n)114Inm have been measured by the activation method. The neutron flux at energies below 5.1 MeV was determined with a calibrated neutron long counter while at higher energies, measurements were made relative to the known cross section for the 32S(n,p) reaction. Effective cross sections for a 235U fission-neutron spectrum calculated from our measured excitation curves are 173 ± 9 mb for 115In(n,n′)115Inm, 123 ± 24 mb for 113In(n,n′)113Inm, and 0.64 ± 0.06 mb for 115In(n,2n)114Inm.

scholarly journals Absolute cross section measurements of 238U(n,f) and 237Np(n,f) in the neutron energy range 1-2.4 MeV

2019 ◽  
Vol 211 ◽  
pp. 03009
Author(s):  
Paula Salvador-Castiñeira ◽  
Franz-Josef Hambsch ◽  
Alf Göök ◽  
Marzio Vidali ◽  
Nigel P. Hawkes ◽  
...  
Keyword(s):  
Cross Section ◽  
Neutron Energy ◽  
Cross Sections ◽  
Energy Region ◽  
Power Plants ◽  
National Physical Laboratory ◽  
Absolute Cross Section ◽  
Neutron Energy Range ◽  
Physical Laboratory ◽  
Low Energies

New standard (n,f) cross sections other than 235U are important to study the relevant cross sections for Generation-IV power plants. A specific need for such standards is for performing new experiments with quasimonoenergetic neutron beams, such as those produced by Van de Graaf accelerators. Neutrons down-scattered to low energies in the experimental environment, so called room-return, become relevant for this type of measurements. Hence, a standard (n,f) cross section with a fission threshold is of great interest, in order to suppress the contribution from room-return background. For this reason we have performed two experiments at the VDG of the National Physical Laboratory to measure absolutely the (n,f) cross sections of 235U, 238U and 237Np in the fast neutron energy region. Our preliminary results are in agreement with the most up-to-date evaluations.

Fission Cross-Section Measurements of241Am between 0.1 eV and 10 keV with Lead Slowing-Down Spectrometer and at Thermal Neutron Energy

1997 ◽  
Vol 126 (2) ◽  
pp. 201-212 ◽  
Author(s):  
Shuji Yamamoto ◽  
Katsuhei Kobayashi ◽  
Mitsuharu Miyoshi ◽  
Itsuro Kimura ◽  
Ikuo Kanno ◽  
...  
Keyword(s):  
Thermal Neutron ◽  
Cross Section ◽  
Neutron Energy ◽  
Fission Cross Section ◽  
Slowing Down

A comparison of some absolute methods of measuring fast neutron flux

1950 ◽  
Vol 46 (2) ◽  
pp. 339-352 ◽  
Author(s):  
K. W. Allen ◽  
D. L. Livesey ◽  
D. H. Wilkinson
Keyword(s):  
Neutron Flux ◽  
Fast Neutron ◽  
Cross Sections ◽  
Absolute Measurement ◽  
Fast Neutrons ◽  
Fast Neutron Flux ◽  
Cavendish Laboratory ◽  
The Individual ◽  
Nuclear Processes

The absolute measurement of fast neutron flux presents several difficult problems. Few methods have yet been described in the literature, although the experimental techniques developed by several authors for the detection of fast neutrons (Baldinger, Huber and Staub(7), Barshall and Kanner(9), Amaldi, Bocciarelli, Ferretti and Trabacchi (3), Gray (19), Barshall and Battat(8)) may easily be adapted to this type of measurement. It is, however, most important to have available methods of measuring fast neutron flux to permit the determination of cross-sections for nuclear processes induced by fast neutrons, and several such methods have been developed in the Cavendish Laboratory in recent years. They are the subjects of separate papers (Bretscher and French (13), Kinsey, Cohen and Dainty (21), Allen (l), Allen and Wilkinson (2)). The main purpose of the present paper is to describe the results of experiments carried out to compare these methods in order to test the validity of the assumptions implicit in the individual methods.

Sign in / Sign up

Export Citation Format

Share Document