Double-differential Neutron Emission Cross Sections Research Articles

Calculations of Double-Differential Neutron and Proton Emission Cross Sections on 19F at 14.2-MeV Incident Neutron Energy

In the present paper, the double-differential cross sections (d2σ/dΩde) of emission spectra for the 19F(n, xn) and 19F(n, xp) structural fusion materials (contained in FLiBe) were calculated by using the Hybrid Monte-Carlo Simulation at 14.2-MeV incident neutron energy in emission angles ranging from 30◦ to 150◦. Theoretical model calculations were carried out by using ALICE-2011, EMPIRE, and TALYS computer codes. Theoretically calculated results of the double-differential cross section for neutron and proton emission are presented and compared with the existing experimental data taken from the international nuclear reaction EXFOR database.

Measurement of differential and double-differential neutron emission cross-sections for 9Be at 21.94 MeV neutrons

The secondary neutron emission differential and double-differential cross sections (DX and DDXs) of n + 9Be have been measured at the neutron energy of 21.94MeV using the multi-detector fast neutron time-of-flight (TOF) spectrometer. The data was derived by comparing the measured TOF spectra with detailed Monte Carlo simulation, and corrected with n-p scattering cross section. Meanwhile, theoretical calculations based on the Hauser-Feshbach and exciton model have been performed to compare with experimental data. Measured differential cross sections were also compared with other measurements. It was found that the experimental results were in agreement with other measurements and theoretical calculations, while discrepancies were also present in the whole energy region and at some angles.

Angle-Dependent Double-Differential Neutron Emission Cross Sections of 3H(t,n) between 5.98 and 19.14 MeV and Evidence of 4H as Intermediate Reaction Product

Neutrons for fusion applications stem not only from monoenergetic sources but also from “white” neutron sources. In this regard, the reaction 3H(t,n) is of particular interest. Continuous neutron spectra of the 3H(t,n) reactions were measured at 5.98-, 7.47-, 10.45-, 16.41-, and 19.14-MeV triton energy at typically seven angles between 0 and 145 deg. The spectra at the three lowest energies contain only neutrons from 3H(t,n)5He and 3H(t,2n)4He reactions and therefore can more easily be interpreted than the spectra at 16.41 and 19.14 MeV, which are too complex to allow a straightforward decomposition except for estimation of the neutron emission cross section following the reaction 3H(t,d)4H. Angle-dependent double-differential and neutron energy—integrated cross sections are given at the five energies. In most cases the peak of the two-body ground state transition could be deconvolved reliably resulting in cross sections of the reaction 3H(t,n)5He. Although the basic scale uncertainty is >5%, severe background, in particular, at the higher triton energies, increases the total uncertainty of integrated cross sections up to 9%. Naturally, the uncertainty of each energy bin of the double-differential cross sections, which depend on bin width, is considerably higher. As no previous data are reported at or near these energies, no direct comparison with other data was feasible. Evidence is provided of the formation of the short-lived neutron-rich nuclei 5He and at higher energies of 4H.

Neutron Emission Spectra of Triton Beams of 20.22-MeV Fully Stopped in Targets of H2O, D2O, LiF, Si, Ni, Mo, Ta, W, Pt, and Au

The Ion Beam Facility of Los Alamos National Laboratory could routinely provide accelerated bunched triton beams to be used in neutron time-of-flight experiments. Exploratory measurements at 0 deg were done to determine the neutron yield with target materials throughout the periodic system yielding absolute specific double-differential neutron yields. Only a few of these measurements were made public previously. The results of these measurements having a mainly demonstrative purpose are presented here because of their uniqueness. For lithium and beryllium, double-differential neutron emission cross sections are given at 17.2 and 15.2 MeV, respectively.

Calculations of Double-Differential Neutron Emission Cross Sections for 9Be Target Nucleus at 14.2 MeV Neutron Energy

In this study, we investigated neutron-emission spectra induced by (n,xn) nuclear reactions for the 9Be structural fusion material at 14.2 MeV neutron energy. We calculated double-differential cross sections (\({\raise0.7ex\hbox{${d^{2} \sigma }$} \!\mathord{\left/ {\vphantom {{d^{2} \sigma } {d\varOmega d\varepsilon }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${d\varOmega d\varepsilon }$}}\)) with ALICE-2011 codeor the angles of 30°, 60°, 90°, 120°, and 150°. Hybrid Monte Carlo simulation model have been used to calculate the double differential emission spectra for these different angles. The obtained results were compared with the measured data taken from EXFOR library. The results show an acceptable agreement.

Theoretical analysis of double-differential neutron emission cross sections for n+56Fe reactions at incident energies of 7–13 MeV

The double-differential neutron emission cross sections for n+56Fe reactions at incident energies of 7–13 MeV at different angles are calculated by the UNF (abbreviation for unified, 2009 Version) code, which is based on the unified Hauser-Feshbach and exciton model. The results indicate that the higher the incident energies, the better the results, although there are some discrepancies between the calculated results and the measured data for natural iron. These discrepancies are analyzed in detail in this paper. In addition, the calculated results are also compared with the evaluated results of ENDF/B VII.0 and JEFF-3.1.1 near the angle of 90° at incident energies of 8.17 and 11.5 MeV, respectively.

Experimental studies of neutron emission spectra in Li(d,xn) reactions for IFMIF

To improve the accuracy of the neutron emission data in the natLi(d,xn) reaction, which will be used as the neutron source in the International Fusion Materials Irradiation Facility (IFMIF), we measured the double-differential neutron emission cross-sections (DDXs) of the d-Li reaction at 25MeV at the cyclotron facility of Tohoku University. The DDXs were measured at ten laboratory angles between 0° and 110° by the time-of-flight method, using a beam-swinger system and a well-collimated neutron flight channel. We used a two-gain method to obtain over most of the energy range of secondary neutrons and reveal the shape of the overall emission spectra including the breakup peak of incident deuterons near half the incidence energy, and several peaks in the high-energy tail due to stripping reactions. The experimental results compared favorably with those obtained using the extended Serber model.

Double-Differential Neutron Emission Cross-Section Measurements of 6Li and 7Li at Incident Neutron Energies of 8.17 and 10.27 MeV

Energy angular neutron emission double-differential cross sections (DDXs) of 6Li and 7Li were measured at incident neutron energies of 8.17 and 10.27 MeV, respectively, using normal and normal + abnormal fast neutron time-of-flight (TOF) spectrometers. The effects of breakup neutrons from a D(d,n) source and the influence of an aluminum container of Li samples, as well as 7Li in the 6Li sample and 6Li in the 7Li sample, on the secondary neutron spectra were eliminated. The data were derived by comparing the net TOF spectra with the calculated spectra using a realistic Monte Carlo simulation. The differential cross sections were determined by comparing the measured and simulated TOF spectra with respect to specific scattering fractions, i.e., with respect to the elastic lines and the resolved inelastic lines related to single levels or level groups, and normalized to n-p scattering. The angular distributions for the 6Li and 7Li elastic and inelastic neutron scattering were obtained also. The angle-integrated cross sections were derived for elastic scattering from 6Li and for the sum of elastic and 0.478-MeV state inelastic scattering from 7Li. Inelastic scattering cross sections were obtained for the 2.186-MeV state in 6Li and the 4.652-MeV state in 7Li. Meanwhile, based on the unified Hauser-Feshbach and exciton model, the calculated results of the DDXs for n + 6,7Li were compared with measurements.

Measurement and analysis of the energy–angular distribution of secondary neutrons for 9Be at 5.9 and 6.4 MeV incident neutrons

The energy-angle double-differential neutron emission cross-sections of beryllium have been measured using the time of flight technique for 5.9 and 6.4 MeV incident neutrons, respectively, at 10 laboratory angles between 25° and 150°. The measured results are compared with model calculations based on the LUNF code and those of other authors and the ENDF/B-VII data. The estimation of the inelastic scattering neutron cross-sections leaving 9Be ∗ at the low-lying level states are also theoretically analyzed by the LUNF code. The experimental and calculated results indicated that the lowest (1.68 MeV) level still contributes to the ( n, 2 n) reaction with cross-sections of several 10 mb. The angular distributions and the angle-integrated elastic scattering cross-sections are also presented in comparison with other ones, these being in good agreement with the ENDF/B-VII data.

Measurement of the 28Si(n,p), 29Si(n,p) and 30Si(n,α) Cross Sections between 6.9 and 14.0 MeV

Neutron activation cross sections of 28Si(n, p)28Al, 29Si(n, p)29Al and 30Si(n, α)27Mg were measured in the energy region from 7 to 14 MeV. The measurements were performed with a D(d, n)3He neutron source and were carefully corected for disturbing neutrons from the D(d, np) breakup reaction. The corrections are based on a detailed measurement of the double-differential neutron emission cross sections of the neutron source reaction. The present work is the only experiment which covers the neutron energy range from 7 to 13 MeV of the 29Si(n, p)29Al and 30Si(n, α)27Mg reaction, and that from 9 to 12.5 MeV of the 28Si(n, p)28Al reaction.

Measurements of double-differential neutron emission cross-sections of 238U and 232Th for 2.6, 3.6 and 11.8 MeV neutrons

Double-differential neutron emission cross-sections (DDXs) of 238U and 232Th were measured for 2.6, 3.6 and 11.8 MeV incident neutrons using a time-of-flight (TOF) method at the Tohoku University 4.5 MV Dynamitron accelerator facility. In DDXs for En=2.6 MeV, discrete structures by vibrational level groups are visible clearly around excitation energy (Ex) around 0.75 and 1.15 MeV, while inelastic scattering to continuum-levels become dominant at En=3.6 MeV for both nuclei. For En=11.8 MeV, continuum structures with strong forward peaking are dominant with some discrete structures at around 0.7–4.0 MeV excitation energy for both of 238U and 232Th. Partial cross-sections for the elastic and inelastic scattering processes were also derived from the DDX data.

Measurements of Double-Differential Neutron Emission Cross Sections of 6Li, 7Li and 9Be for 11.5 MeV and 18.0 MeV Neutrons

Double-differential neutron emission cross sections (DDXs) of 6Li, 7Li and 9Be were measured for 18.0 MeV and 11.5 MeV incident neutrons produced by the T(d, n) and 15N(d, n) reactions respectively, using the Tohoku University Dynamitron time-of-flight (TOF) spectrometer. The data were obtained at 13 laboratory angles, and angular-differential cross sections (ADXs) of elastic and inelastic scattering neutrons were derived from the DDXs. For 11.5 MeV neutrons, we obtained the neutron emission spectra over the secondary neutron energies by newly employing the double TOF method as well as the conventional one. In the measurements at 18.0 MeV, we achieved better energy resolution than in our previous studies by using a neutron detector that has a larger solid angle and a thinner tritium target. The experimental results of DDXs and ADXs were compared with our previous results and the evaluated data given in JENDL-3.2, JENDL Fusion File and ENDF/B-VI. It is found that the JENDL data reproduce the experimental ones very well.

Measurements of Double-Differential Neutron Emission Cross Sections of 6Li, 7Li and 9Be for 11.5 MeV and 18.0 MeV Neutrons.

Measurements of Double-Differential Neutron Emission Cross Sections of 6Li, 7Li and 9Be for 11.5 MeV and 18.0 MeV Neutrons.

Double-differential neutron emission cross sections of 14-MeV neutron induced reactions on Na and Pb

The energy and angular distribution of secondary neutrons from the interaction of 14-MeV neutrons with sodium and natural lead were investigated. Absolute double-differential neutron emission cross sections were measured for reaction angles from 30\ifmmode^\circ\else\textdegree\fi{} to 150\ifmmode^\circ\else\textdegree\fi{} in steps of 15\ifmmode^\circ\else\textdegree\fi{} in the secondary neutron energy range 2--14 MeV using the time-of-flight facility at the Institut f\"ur Radiumforschung und Kernphysik, Vienna. Systematic uncertainties in these measurements could be reduced to less than 3--5% (depending on secondary neutron energy) resulting in total uncertainties of less than 5% for a large part of the studied range in angle and energy for Pb and of less than 8% for Na. These results agree with previous measurements within the relatively large uncertainties of the latter. The measured cross sections were compared to the results of statistical model calculations using the quantum mechanical theory of Feshbach, Kerman, and Koonin for preequilibrium emission and also with calculations based on the exciton model and the Kalbach-Mann systematics for the shape of the angular distributions. For compound nucleus decay, the Hauser-Feshbach model was used in both cases. Very good agreement was found with both predictions in the case of lead; in the case of sodium, noticeable discrepancies do show the limits of applicability of any statistical model for light nuclei.

Gradual absorption of fast neutrons in niobium

Single- and double-differential neutron-emission cross sections for niobium, at bombarding neutron energies of 7, 14, 20 and 26 MeV, have been adequately explained in terms of direct reactions accompanied by gradual absorption into successive compound states of increasing complexity which develop towards the compound nucleus.

Measurements of Double-Differential Neutron Emission Cross Sections of Nb, Mo, Ta, W and Bi for 14 and 18 MeV Neutrons

Measurements of Double-Differential Neutron Emission Cross Sections of Nb, Mo, Ta, W and Bi for 14 and 18 MeV Neutrons

A compact post-acceleration beam chopper for a 4.5 MV Dynamitron pulsed neutron generator

A post-acceleration beam chopper (PACS) has been installed for a 4.5 MV Dynamitron accelerator to improve the energy resolution of neutron time-of-flight (TOF) experiments by shortening the duration of the ion beam pulses. The PACS sweeps the accelerated ion pulses across a chopping slit and eliminates the tails of the beam pulses. It operates sinusoidally at a frequency of 8 MHz with a maximum voltage of 10 kV peak to peak in synchronization with the accelerated ion pulses. The high voltage generator of the PACS was constructed of commercially available amplifiers and components, which realized easy maintenance and low cost. The PACS proved to be very effective to improve the pulse shape and has been applied for double-differential neutron emission cross section measurements.

Measurements of Double-Differential Neutron Emission Cross Sections of Nb, Mo, Ta, W and Bi for 14 and 18 MeV Neutrons.

Double-differential neutron emission cross sections have been measured for Nb, Mo, Ta, W and Bi at 14 MeV incident energy, and for Nb and Bi at 18 MeV using Tohoku University Dynamitron TOF spectrometer. The experimental results indicated problems in current evaluations both for energy spectra and angular distributions. Angle-integrated neutron emission spectra and angular distributions of secondary neutrons were analyzed, respectively, by the statistical multi-step model code EXIFON and the systematics by Kalbach-Mann and by Kalbach. The energy spectra were reproduced successfully by EXIFON except for Bi, and the angular distributions were followed by the systematics over wide range of outgoing energy and target mass if the emission spectra calculated by EXIFON were employed for generation of angular distributions.

Neutron emission cross sections on 93Nb and 209Bi at 20 MeV incident energy

Double-differential neutron emission cross sections at 20 MeV incident energy have been studied for monoisotopic samples of 93Nb and 209Bi. Time-of-flight spectra were taken at several angles between 15° and 153° using a beam-swinger spectrometer. The data are averaged over 0.5 MeV energy bins and compared with quantum-mechanical, statistical multistep calculations.

Requirements and status of fast neutron cross sections for nuclear fusion

This paper discusses some of the requirements of fast neutron cross sections for the development of tokamak fusion reactor technology and their current status. While considerable progress has been achieved in knowledge of fast neutron scattering and reaction cross sections of fusion reactor materials, much work needs still to be done particularly on double-differential neutron emission and neutron activation cross sections, in particular (n,α) cross sections. Particular consideration has been given to the work of Professor Csikai and co-workers who have rendered essential contributions to the measurement and analysis of 14 MeV neutron cross sections of importance to fusion.