Neutron-induced Reaction Cross Sections Research Articles

Neutron-induced dosimetry reaction cross-section measurements from the threshold up to 20 MeV

New measured results were obtained for the (58)Ni(n,p)(58)Co, (58)Ni(n,2n)(57)Ni, (58)Ni(n,x)(57)Co, (60)Ni(n,p)(60)Co, (59)Co(n,2n)(58)Co, (59)Co(n,p)(59)Fe, (63)Cu(n,alpha)(60)Co, (204)Pb(n,n')(204 m)Pb and (204)Pb(n,2n)(203)Pb reaction cross-sections. These reactions may be of interest for dosimetry. Measurements were taken at the 7 MV Van de Graaff accelerator at IRMM, Geel, using the activation technique in combination with high-resolution gamma ray spectrometry. The present results are compared with other measurements, evaluated data and model calculations.

Development of a Comprehensive Code for Nuclear Data Evaluation, CCONE, and Validation Using Neutron-Induced Cross Sections for Uranium Isotopes

A new comprehensive code for nuclear data evaluation, CCONE, has been developed for the evaluation of nuclear data for actinides. Neutron-induced reaction cross sections for uranium isotopes (A = 232, 233, 234, 235, 236, 237, 238) were analyzed for incident energies from 10keV to 20MeV using CCONE in order to validate its capability. Reproducibility of the cross section calculations for various reactions such as total, fission, capture, and (n, 2n) was tested using simple parameterization. The calculated cross sections and neutron emission spectra show good agreement with the experimental data.

Cross section measurements for neutron-induced reactions off C, Al, SiO2, Si and Au producing relatively short-lived radionuclides at neutron energies between 70 and 160 MeV

A systematic study was made to measure many cross sections for relevant neutron-induced reactions. This study was motivated by the need to better understand cosmic ray interactions with extraterrestrial materials. The major constituents of meteorites and lunar rocks include oxygen, silicon, and aluminum. The primary aim was to measure cross sections for neutron-induced reactions producing long-lived radionuclides (e.g. 14C) and stable isotopes (e.g. Ne isotopes) but the irradiation conditions allowed cross sections for many reactions producing relatively short-lived radionuclides (e.g. 22Na) to be well measured. Monitor foils used in the irradiations included C, Al, and Au. Quasi-monoenergetic neutron beams were produced by bombarding Be targets with 80, 120 and 160MeV proton beams at iThemba LABS, South Africa. Two identical target stacks were irradiated in beam lines at 0° and 16° to the incident proton beam direction. The yield at an unique neutron energy was obtained by subtracting the yield measured at 16° (after suitable normalization) from that measured at 0°. The cross sections for the following reactions: 27Al(n,x)22,24Na; natC(n,x)7Be; 197Au(n,x)194,196Au; SiO2(n,x)22Na and natSi(n,x)24Na are reported.

The shell structure effects in neutron cross section calculation by a theoretical model code

The role of the shell structure properties of the nucleus in the calculation of neutron-induced reaction cross-section data based on nuclear reaction theory has been investigated. In this investigation, measured, evaluated and calculated (n.p) reaction cross-section data on la spherical nucleus (i.e. 112Sn) and a deformed nucleus (i.e. 150Nd) were compared. To obtain the calculated data, nuclear model calculation as carried out using the EXIFON calculational code based on a global set of input parameter with the shell structure effect as the only adjustable parameter. The measured and evaluated and calculated data were retrieved from EXFOR and JENDL-3-3 data libraries respectively. A comparison of measured, evaluated and calculated data indicates that calculation in which the shell effect was considered adequately describe experimental data for the deformed nucleus in the 14MeV neutron energy region. Similarly, the calculated data in which the shell structure correction was ignored agree well with measured and evaluated data for the spherical nucleus. Nigerian Journal of Physics Vol. 16(2) 2004: 81-85

Uncertainty in cross-section calculations for reactions induced by neutrons with energy above 0.1 MeV

Abstract The uncertainty in the calculation of neutron induced reaction cross-sections using modern nuclear models and codes has been investigated. The cross-sections have been calculated with the help of the TALYS code and the modified ALICE code using different models for the calculation of nuclear level density. The experimental data from EXFOR for neutron induced reactions for nuclei from 27Al to 209Bi and incident neutron energies above 0.1 MeV have been used for the comparison with calculations. The results obtained give the possibility to find the best approaches for the cross-section calculation for nuclei from different mass ranges.

Cross section measurements for neutron-induced reactions in Ti, Fe and Ni at several neutron energies ranging from 70.7 to 151.6 MeV

Cross sections for neutron-induced reactions producing relatively short-lived radionuclides were measured in natural targets of Ti, Fe and Ni using quasi-monoenergetic neutron beams at several different neutron energies between 70.7 and 151.6 MeV. Comparisons of these new measurements were made with energy integrated cross section measurements and reported data measured at low neutron energies as well as with MC-ALICE calculations. These cross section measurements are part of a systematic study to measure relevant cross sections needed to better understand cosmic ray interactions with extraterrestrial materials.

Global Comparison of TALYS and ALICE Code Calculations and Evaluated Data from ENDF/B, JENDL, FENDL, and JEFF Files with Measured Neutron Induced Reaction Cross-sections at Energies above 0.1 MeV

The neutron induced reaction cross-sections for target nuclei from 27Al to 209Bi and incident neutron energies above 0.1 MeV have been calculated with the TALYS code and the modified ALICE code using different models for the description of the nuclear level density. Several thousand experimental points from EXFOR have been used for the comparison with these calculations. The obtained results give the possibility to find the best approaches for the cross-section calculation for nuclei in different mass ranges.

Maxwellian-averaged neutron-induced reaction cross sections and astrophysical reaction rates for kT = 1 keV to 1 MeV calculated from microscopic neutron cross section library JENDL-3.3

Maxwellian-averaged cross sections and astrophysical reaction rates were calculated for neutron capture, fission, (n,p), (n,α), and some threshold reactions based on a microscopic neutron cross section data library, the Japanese Evaluated Nuclear Data Library Version 3.3 (JENDL-3.3). The calculation was made for temperatures ( kT) from 1 keV to 1 MeV including the most important range in astrophysical nucleosynthesis. Results are presented in the tables and graphs. The Maxwellian-averaged neutron capture cross sections are compared with recommendations of other authors. Implications of the differences between the present data and previous ones to s-process nucleosynthesis are discussed.

Cross-section measurements for neutron-induced reactions in copper at neutron energies of 70.7 and 110.8 MeV

Cross-sections for neutron-induced reactions on copper producing relatively short-lived radionuclides were measured at incident neutron energies of 70.7 and 110.8MeV. These measurements were made using quasi-monoenergetic neutrons obtained from the Be+p reaction. Corrections were made for the contribution of the low energy tail in the incident neutron spectrum of these measurements. The measured cross-sections were compared with some of the few reported cross-section measurements for neutron-induced reactions at high energies, theoretical cross-sections calculated using MC-ALICE and with the cross-sections for the corresponding proton-induced reactions.

Measurements of the 90,91,92,94,96Zr( n, γ) cross-sections at n_TOF

Neutron capture cross sections of the 90,91,92,94,96 Zr have been measured over the energy range from 1 eV to 1 MeV at the spallation neutron facility n_TOF at CERN in 2003. The innovative features of the neutron beam, in particular the high instantaneous flux, the high energy resolution and low background, together with improvements of the neutron sensitivity of the capture detectors make this facility unique for neutron-induced reaction cross section measurements with much improved accuracy. The preliminary results of the Zr measurements show capture resonance strengths generally smaller than in previous measurements.

Estimation of (n,f) cross sections by measuring reaction probability ratios

Neutron-induced reaction cross sections on unstable nuclei are inherently difficult to measure due to target activity and the low intensity of neutron beams. In an alternative approach, named the ``surrogate'' technique, one measures the decay probability of the same compound nucleus produced using a stable beam on a stable target to estimate the neutron-induced reaction cross section. As an extension of the surrogate method, in this paper we introduce a new technique of measuring the fission probabilities of two different compound nuclei as a ratio, which has the advantage of removing most of the systematic uncertainties. This method was benchmarked in this report by measuring the probability of deuteron-induced fission events in coincidence with protons, and forming the ratio $P[^{236}\mathrm{U}(d,\mathrm{pf})]/P[^{238}\mathrm{U}(d,\mathrm{pf})]$, which serves as a surrogate for the known cross section ratio of $^{236}\mathrm{U}(n,f)/^{238}\mathrm{U}(n,f)$. In addition, the $P[^{238}\mathrm{U}(d,{d}^{'}f)]/P[^{236}\mathrm{U}(d,{d}^{'}f)]$ ratio as a surrogate for the $^{237}\mathrm{U}(n,f)/^{235}\mathrm{U}(n,f)$ cross section ratio was measured for the first time in an unprecedented range of excitation energies.

Measurements of energy integrated cross sections for reactions producing relatively short-lived radionuclides using neutron beams with an energy range of 0.1–750 MeV

Energy integrated cross sections for neutron-induced reactions producing relatively short lived radionuclides were measured using ‘white’ neutron beams with an energy range of 0.1–750 MeV at the Los Alamos Neutron Science Center (LANSCE). Cross sections for neutron-induced reactions are needed as input to the theoretical models used to understand the production of the radionuclide and stable isotopes produced by cosmic ray interactions with extraterrestrial bodies. Although most primary cosmic rays are protons, significant quantities of short- and long-lived radionuclides and stable isotopes are produced by spallation reactions initiated by secondary neutrons produced in primary cosmic ray interactions. Materials irradiated contained the elements commonly found in lunar rocks and meteorites, including SiO 2 (for O), Si, CaCO 3 (for Ca), Al, Mg, Fe, Ni and KNO 3 (for K).

Double differential neutron emission cross sections for n + 230,231,232,233,234Th reactions

Consistent calculation and analysis of neutron-induced reaction cross sections of 232Th with optical model, the unified Hauser–Feshbach and exciton model, the linear angular momentum dependent exciton density model, the coupled channel theory and the distorted wave Born approximation is carried out in the E n ⩽ 20 MeV energy range based on the experimental data of total, nonelastic, fission, and other reaction cross section and elastic scattering angular distributions. Especially, the analysis includes the elastic and inelastic scattering angular distribution, the inelastic scattering cross sections of discrete levels, the prompt fission neutron spectra, the double differential cross section and the angle-integrated spectra for neutron emission. Theoretical calculations are compared with recent experimental data, other theoretical calculations and evaluated data from ENDF/B6 and JENDL-3. Theoretical models predict the results for n + 230,231,233,234Th reactions.

Neutron-induced nuclear reactions and degradation in germanium detectors

We have measured cross sections of neutron-induced nuclear reactions leading to the delayed production of gamma-ray lines similar to the ones of astrophysical interest. Conclusions were drawn concerning the expected background in the Al-26 1809 keV line and the Be-7 478 keV line in SPI. The neutron-induced degradation of Ge detectors was studied vs. the neutron energy, the neutron fluence and the detector temperature. Performance recovery of the detectors was studied for different annealing temperatures. Optimum temperature and times for annealing were determined.

A new empirical formula for 14–15 MeV neutron-induced (n, p) reaction cross sections

In this study, we have suggested a new empirical formula to reproduce the cross sections of the (n, p) reactions at 14–15 MeV for the neutron incident energy. This formula obtained using the asymmetry parameters represents a modification to the original formula of Levkovskii. The resulting modified formulae yielded cross sections, representing smaller χ2 deviations from experimental values, and values much closer to unity as compared with those calculated using Levkovskii's original formula. The results obtained have been discussed and compared with the existing formulae, and found to be well in agreement, when used to correlate the available experimental σ(n, p) data of different nuclei.

Measuring neutron-induced fission cross-section of shortlived actinides using a lead neutron-slowing-down spectrometer

The “lead-slowing-down-spectrometer” method is an established technique for measuring neutron-induced reaction cross-sections. It is known to provide high neutron fluences below 100 keV . In this work, the possibility of applying this method to the measurement of the neutron-induced fission cross-section of shortlived actinides and in particular of the 77 eV isomer of 235 U is investigated. Numerical simulations and a test-experiment using a photovaltaic cell fission detector demonstrate the feasibility of such a measurement at the Los Alamos Neutron Science Center using 800 MeV proton-induced spallation to provide source neutrons.

Computational Experience with the Reich-Moore Resolved-Resonance Equations in the AMPX Cross-Section Processing System

The Reich-Moore (RM) formulation is used extensively in many isotope/nuclide evaluations to represent neutron cross-section data for the resolved-resonance region. The RM equations require the evaluation of complex matrices (i.e., matrices with complex quantities) that are a function of the resonance energy and corresponding resonance parameters. Although the RM equations are documented in the open literature, computational pitfalls may be encountered with the implementation of the RM equations in a cross-section processing code. Based on experience, numerical instabilities in the form of nonphysical oscillations can occur in the calculated absorption, capture, or elastic scattering cross sections. To illustrate possible numerical instabilities, the conventional RM equations are presented, and the conditions that lead to numerical problems in the cross-section calculations are identified and demonstrated for 28Si and 60Ni. In an effort to circumvent the computational problems, detailed or revised RM expressions have been developed to efficiently and accurately calculate cross sections for neutron-induced reactions in the resolved-resonance region. The revised equations can be used to avoid numerical problems associated with the implementation of the RM formulation in a cross-section processing code. The revised Reich-Moore equations are also used to demonstrate the improved cross-section results (i.e., without numerical instabilities) for 28Si and 60Ni.

Data Library IEAF-2001 to Study of Activation of Irradiated Materials

The IEAF-2001 library comprises a collection of individual files for a large number of target nuclides. Each file contains data for neutron-induced reaction cross sections for energies from 10-5 eV to 150 MeV. The target nuclides cover the range from Z=1 to Z=84 i.e. from H to Po. The total amount of the IEAF-2001 library is 679 data files including stable, unstable and isomeric target nuclides. 58 data files correspond to first isomeric states of the target nuclides and 4 files to second target isomers.

Neutron-induced reaction cross-section measurements using a small multi-detector array and description of a large array

The experimental setup of Louvain-1a-Neuve (UCL-Belgium) used to perform light-charged particle production experiment in fast neutron-induced reactions is presented. A short description of the neutron modular detector DEMON is also given. DEMON is a detector array for neutrons emitted in heavy ion induced reactions at low to intermediate energies.

Advances in cross section measurements at low energies

A systematic study was made to measure many cross sections for relevant neutron-induced reactions. This study was motivated by the need to better understand cosmic ray interactions with extraterrestrial materials. The major constituents of meteorites and lunar rocks include oxygen, silicon, and aluminum. The primary aim was to measure cross sections for neutron-induced reactions producing long-lived radionuclides (e.g. 14C) and stable isotopes (e.g. Ne isotopes) but the irradiation conditions allowed cross sections for many reactions producing relatively short-lived radionuclides (e.g. 22Na) to be well measured. Monitor foils used in the irradiations included C, Al, and Au. Quasi-monoenergetic neutron beams were produced by bombarding Be targets with 80, 120 and 160 MeV proton beams at iThemba LABS, South Africa. Two identical target stacks were irradiated in beam lines at 0° and 16° to the incident proton beam direction. The yield at an unique neutron energy was obtained by subtracting the yield measured at 16° (after suitable normalization) from that measured at 0°. The cross sections for the following reactions: 27Al(n,x)22,24Na; natC(n,x)7Be; 197Au(n,x)194,196Au; SiO2(n,x)22Na and natSi(n,x)24Na are reported.