Nonelastic-scattering Cross Sections Research Articles

ENDF/B-VIIIβ4 benchmark test with iron and concrete shielding experiments using 40 and 65 MeV neutrons at QST/TIARA

The latest beta version of ENDF/B-VIII, ENDF/B-VIIIβ4 was released in February 2017 from the Cross Section Evaluation Working Group. We benchmarked the iron and concrete shielding experiments with 40 and 65MeV neutrons at QST/TIARA by using ENDF/B-VII.1, JENDL-4.0/HE and ENDF/B-VIIIβ4 to investigate whether the 56Fe and 16O data in ENDF/B-VII.1 were properly improved in ENDF/B-VIIIβ4 or not. The drastic overestimation in the calculated result with ENDF/B-VII.1 was resolved in that with ENDF/B-VIIIβ4 in the iron experiment with 40MeV neutrons, because of the revision of the non-elastic scattering cross section data of 56Fe in ENDF/B-VIIIβ4. However, the calculated result with ENDF/B-VIIIb4 significantly underestimated the measured one in the experiment with 65MeV neutrons. The drastic overestimation in the calculated results with ENDF/B-VII.1 still appeared in those with ENDF/B-VIIIβ4 in the concrete experiments with 40 and 65MeV neutrons, due to no improvement of 16O data particularly above 20MeV in ENDF/B-VIIIβ4. We figured out that the effect of the 16O data replacement was very large and those of 28Si and 27Al data replacements were also not so small. The official release of ENDF/B-VIII should be produced based on this study.

JENDL-4.0/HE Benchmark Test with Concrete and Iron Shielding Experiments at JAEA/TIARA

As a benchmark test of JENDL-4.0/HE released in 2015, we have analyzed the concrete and iron shielding experiments with the quasi mono-energetic 40 and 65 MeV neutron sources at TIARA in JAEA by using MCNP5 and ACE files processed from JENDL-4.0/HE with NJOY2012. As a result, it was found out that the calculation results with JENDL-4.0/HE agreed with the measured ones in the concrete experiment well, while they underestimated the measured ones in the iron experiment with 65 MeV neutrons more for the thicker assemblies. We examined the 56 Fe data of JENDL-4.0/HE in detail and it was considered that the larger non-elastic scattering cross sections of 56 Fe caused the underestimation in the calculation with JENDL-4.0/HE for the iron experiment with 65 MeV neutrons.

Theoretical Calculations and Analysis of n + 27Al Reaction

All cross sections of neutron-induced reactions, angular distributions, energy spectra, and double-differential cross sections are consistently calculated and analyzed for n + 27Al reactions at incident neutron energies below 200 MeV based on the nuclear theoretical models. The optical model; the unified Hauser-Feshbach theory and exciton model, which includes the improved Iwamoto-Harada model; and the distorted wave Born approximation theory are used. Theoretical calculated results are compared with the experimental data and the evaluated results in ENDF/B-VII and JENDL-3. The optical model potential parameters are obtained according to the experimental data of total and nonelastic scattering cross sections and elastic scattering angular distributions.

Novel Investigation of Iron Cross Sections via Spherical Shell Transmission Measurements and Particle Transport Calculations for Material Embrittlement Studies

We have carried out a multifaceted research project to improve our knowledge of the iron nonelastic scattering cross sections. Spherical shell transmission measurements were made using time-of-flight techniques with neutrons from the 15N(p,n)15O and D(d,n)3He source reactions. For the 15N(p,n)15O work, measurements were made with a proton energy of 5.1 MeV. Measurements were made from 3 to 7-MeV deuteron energy for the D(d,n)3He work. For both source reactions, the angular range was as large as 15 to 135 deg. Two shell thicknesses were used. Comparisons are given between Monte Carlo predictions and experimental data.Utilizing a new tallying option, the estimated total iron cross sections at energies corresponding to the peak of the spectra for the 0-deg experiments were calculated to within 1% of the data in the ENDF/B-VII library. A processing code was developed to adjust ENDF format files to obtain closer agreement between measurements and calculations. Sensitivity analyses were performed at energies corresponding to the 0-deg beam angle neutrons. Using cross sections where the nonelastic and elastic cross sections were adjusted while constraining the total cross section to be constant, differences between experiment and calculation were reduced by ~;40% for a pressure vessel calculation. Such fluence calculations with adjusted cross sections indicate possible underestimation of neutron fluence, and therefore more material damage.

Calculation and evaluations for n+ 63,65,nat.Cu reactions

All cross sections of neutron induced reactions, angular distributions, energy spectra and double differential cross sections are consistently calculated and analyzed for n+ 63,65,nat.Cu reactions at incident neutron energies below 200 MeV based on the nuclear theoretical models. The optical model, preequilibrium and equilibrium reaction theories, the distorted wave Born approximation theory are used. Theoretical calculated results are compared with existing experimental data and the evaluated results in ENDF/B-VII and JENDL-3 libraries. The optical model potential parameters are obtained according to the experimental data of total, nonelastic scattering cross sections and elastic scattering angular distributions.

Calculation and Evaluations for n + 54,56,57,58,natFe Reactions

All cross sections of neutron-induced reactions, angular distributions, energy spectra and double-differential cross sections are consistently calculated and analyzed for 54,56,57,58,natFe at incident neutron energies below 200 MeV based on the nuclear theoretical models, which are the optical model, preequilibrium and equilibrium reaction theories, and the distorted wave Born approximation theory. Theoretical calculated results are compared with existing experimental data and the evaluated results in ENDF/B-VII and JENDL-3. The optical model potential parameters are obtained according to the experimental data of total and nonelastic-scattering cross sections, and elastic-scattering angular distributions.

Calculation and Analysis of n + 180,182,183,184,186,natW Reactions in the En ≤ 250 MeV Energy Range

According to the experimental data of total, nonelastic scattering cross sections and elastic scattering angular distributions of tungsten and its isotopes, a set of neutron optical model potential parameters is obtained. All of the reaction cross sections, angular distributions, energy spectra, γ-ray production cross sections, γ-ray production energy spectra, and the double-differential cross section for neutron, proton, deuteron, triton, helium, and alpha emission are calculated and analyzed for n + 180,182,183,184,186,natW at incident neutron energies from 0.1 to 250 MeV based on the nuclear model theory, which combines the optical model, the unified Hauser-Feshbach theory and exciton model, and the coupled channel theory. Theoretical calculations are compared with existing experimental data and other evaluated data from ENDF/B6.8 and JENDL-3.3.

A New Investigation of Iron Cross Sections via Spherical-Shell Transmission Measurements and Particle Transport Calculations

We are engaged in a multi-year project to study neutron scattering interactions in iron, the principal objective of which is to investigate the well-known deficiency that exists in reactor pressure vessel neutron fluence determinations. Specifically, we are using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight measurements of the scattered neutrons, in an effort to precisely determine specific energy regions over which deficiencies in the non-elastic scattering cross section for neutron scattering in iron appear to exist. The analysis of the experimental data involves correlating the data with theoretical calculations of neutron transport through the iron spheres in order to evaluate the degree to which the calculated neutron spectra predict the measured spectra relative to different types of particle interactions. In doing so, we have developed new methodologies for performing neutron transport calculations that will be useful to a range of transport problems. Preliminary results show good agreement between the experimental data and the calculated distribution of neutron flight times over much of the data range, except for the contribution due to breakup neutrons.

New Particle Transport Methods for Design and Optimization of Spherical-Shell Transmission Measurements

This paper discusses new particle transport methods developed for accurate investigation of iron non-elastic scattering cross sections using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight spectroscopy of the scattered neutrons. New calculational techniques based on the deterministic and Monte Carlo methods have been developed for design and optimization of the experiment, and for identification and reduction of experimental uncertainties. The new methods include a new tallying option for the MCNP code and new quadrature sets for the 3-D parallel Sn code PENTRAN. The new tallying option is used to determine the optimum source energy versus target thickness, and among the new quadrature sets, the Pn-Tn with ordinate-splitting technique has resulted in accurate flux distributions as compared to Monte Carlo prediction.

Role of boundary conditions at the anode in the development of an electric field induced avalanche in a gas at low pressure

A dc glow discharge configuration was investigated that includes a flat semitransparent anode situated between two symmetrically positioned cathodes. The transparency of the anode increases the electron path length for ionizing collisions. This leads to a significant increase in the number of free electrons in the discharge volume. The simplicity of the discharge configuration makes it possible to model the electron avalanche in its early stage with proper boundary conditions and without the use of adjustable parameters in both elastic and nonelastic scattering cross sections. The results obtained for hydrogen indicate that the number of free electrons in the discharge can be increased by several orders of magnitude in comparison with a similar discharge configuration but with an opaque anode.

Measurement and Analysis of Fission Rate Distributions of 237Np and 238U in a Polyethylene System with a 65 MeV Neutron Source

Fission rates of 237Np and 238U in a polyethylene (CH2) system were measured with a 65MeV quasi monoenergetic neutron source. Relative fission rate distributions dependent on polyethylene thickness up to about 70 cm were obtained for both nuclides with the experimental error within 7%. The present experiment was analyzed by the NMTC/JAERI code that has been employed for designing accelerator-driven transmutation systems. The fission rates of both 237Np and 238U calculated by the NMTC/JAERI did not agree with the experimental ones. The C/E values for both were about 2.0 at 71.8cm of polyethylene thickness when both experimental and calculated values were normalized to 1.0 at 0.0 cm of polyethylene thickness. A sensitivity analysis of the NMTC/JAERI was performed by changing cross sections and angular distributions of hydrogen and carbon and by employing three options of the intra-nuclear cascade/evaporation calculation of the NMTC/JAERI. The disagreement of the NMTC/JAERI calculation with the experimental values was partially improved by increasing the nonelastic-scattering cross section of carbon and by broadening the elastic-scattering angular distribution of carbon.

Measurement and Analysis of Fission Rate Distributions of 237Np and 238U in a Polyethylene System with a 65 MeV Neutron Source.

Fission rates of 237 Np and 238 U in polyethylene (CH 2 ) system were measured with a 65 MeV quasi monoenergetic neutron source. Relative fission rate distributions dependent on polyethylene thickness up to about 70 cm were obtained for both nuclides with the experimental error within 7%. The present experiment was analyzed by the NMTC/JAERI code that has been employed for designing accelerator-driven transmutation systems. The fission rates of both 237 Np and 238 U calculated by the NMTC/JAERI did not agree with the experimental ones. The C/E values for both were about 2.0 at 71.8cm of polyethylene thickness when both experimental and calculated values were normalized to 1.0 at 0.0 cm of polyethylene thickness. A sensitivity analysis of the NMTC/JAERI was performed by changing cross sections and angular distributions of hydrogen and carbon and by employing three options of the intra-nuclear cascade/evaporation calculation of the NMTC/JAERI. The disagreement of the NMTC/JAERI calculation with the experimental values was partially improved by increasing the nonelastic-scattering cross section of carbon and by broadening the elastic-scattering angular distribution of carbon.

Fast-Neutron Total and Elastic- and Nonelastic-Scattering Cross Sections of Elemental Nickel

Neutron total cross sections of elemental nickel were measured from 1.3 to 4.5 MeV, at intervals of ∼50 keV, with resolutions of 30 to 50 keV and to accuracies of 1 to 2.5%. Neutron differential-el...

On the non-elastic cross section of 14.2 MeV neutrons

Non-elastic scattering cross sections for 14.2 MeV neutrons have been measured for the elements O, Al, Cu, Cd, Sn, W and Pb employing the modified sphere transmission technique. Essentially it involves the simultaneous measurement of neutron transmission at different bias levels of the detector providing scope for better experimental accuracy. An automatic search routine was used to calculate an optical model fit to the data. An average set of parameters was obtained by analysing non-elastic as well as differential elastic cross-section data together.

Neutron Cross-Section Measurements ofC12between 14 and 25 MeV

Measurements of the elastic and nonelastic cross sections for neutrons on $^{12}\mathrm{C}$ have been made over the energy range between 14 and 25 MeV using a spherical shell of scattering material surrounding a stilbene detector. In addition to the known peak in the elastic scattering at 19.5-MeV neutron energy, another has been found at 15.8 MeV. The widths of these peaks at half-maximum are 2.0 and 0.5 MeV, respectively. No resonance structure in the nonelastic scattering cross section was found. With specially designed scatterers, the differential elastic scattering was measured at angles which correspond to the zeros of the first four Legendre polynomials, viz., at 90\ifmmode^\circ\else\textdegree\fi{}, 54.8\ifmmode^\circ\else\textdegree\fi{}, 39.2\ifmmode^\circ\else\textdegree\fi{}, and 30.5\ifmmode^\circ\else\textdegree\fi{}. The excitation function of elastic scattering at these angles showed a similar resonance structure in each case, the weakest being at 90\ifmmode^\circ\else\textdegree\fi{}. Inelastic neutron scattering to the first excited state of $^{12}\mathrm{C}$ was determined between 14 and 21 MeV by measuring the 4.43-MeV $\ensuremath{\gamma}$ rays produced by the decay of this state. A very small peak was found at 15.8 MeV and a broader rise near 19 MeV. The low level of resonant effects in the nonelastic channels suggests that the resonances observed in the elastic cross section are caused by single-particle states, and the differential measurements indicate that they are caused by $p$ waves.

Nonelastic Scattering Cross Section for 8-20 Mev Neutrons

Measurements of the nonelastic scattering cross section for neutrons with energies of 8.2, 9.8, 15.5, 17.0, 18.5, and 20.0 Mev have been made in Cu, Ag, Sn, Pb, and Bi. Cross sections were determined from transmissions through spherical shells. Neutrons of 8.2 and 9.8 Mev were obtained from the reaction ${\mathrm{Be}}^{9}(\ensuremath{\alpha}, n){\mathrm{C}}^{12}$ and the higher energy neutrons from the reaction ${\mathrm{T}}^{3}(d, n){\mathrm{He}}^{4}$. Biased scintillation detectors were used so that lower energyneutrons were not counted. The results show that the nonelastic cross sections decrease slowly with increasing neutron energy, in contrast to the cross sections for elastic scattering which show broad maxima at 7, 13, 13, 18, and 18 Mev, respectively, for Cu, Ag, Sn, Pb, and Bi. The ratio of the nonelastic cross sections to the elastic cross sections vary from a maximum value of 1.05\ifmmode\pm\else\textpm\fi{}0.05 to a minimum value of 0.71\ifmmode\pm\else\textpm\fi{}0.05 in the energy range which was covered.

Nonelastic Scattering Cross Sections for Fast Neutrons

Nonelastic Scattering Cross Sections for Fast Neutrons

Nonelastic Scattering Cross Sections for Fast Neutrons

Measurements have been made of the nonelastic cross sections of neutrons in Be, C, Al, Ti, Cr, Fe, Ni, Cu, Ag, Sn, Pb, and Bi. These cross sections include all processes except elastic scattering. The experiments have been carried out with monoenergetic neutrons of 3.5, 4.7, 7.1, 12.7, and 14.1 Mev. The neutrons were produced with a Van de Graaff accelerator using the nuclear reactions: ${\mathrm{T}}^{3}(p, n){\mathrm{He}}^{3}$, $\mathrm{D}(d, n){\mathrm{He}}^{3}$, and ${\mathrm{T}}^{3}(d, n){\mathrm{He}}^{4}$. Cross sections were determined from transmissions through spherical shells which were 3.8 cm in radius and 2 cm thick. A new type of neutron detector which gives energy information about neutrons and is insensitive to $\ensuremath{\gamma}$ radiation was placed at the center of the spherical shell and was used as a biased detector of neutrons. The results of these experiments show that the nonelastic neutron cross section for 12.7- and 14.1-Mev neutrons is nearly geometrical and is closely approximated by $\ensuremath{\sigma}=\ensuremath{\pi}{(R+\ensuremath{\lambda})}^{2}$, where $R=1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}{A}^{\frac{1}{3}}$. The nonelastic cross sections are roughly constant in the energy range 5 to 14 Mev; below about 5 Mev the cross sections begin to decrease.The elastic cross sections can be obtained by subtracting the nonelastic cross sections from the total cross sections. The variations with energy of the nonelastic and elastic cross sections are quite different.Data with 12.7-Mev neutrons and low counter bias, give the relative number of $\ensuremath{\gamma}$ rays given off per inelastic collision of these neutrons. The number of $\ensuremath{\gamma}$ rays decreases rapidly with increasing atomic number and there are less than 5% as many $\ensuremath{\gamma}$ rays from Bi as from Al, Ti, Cr, and Fe.