The n-p scattering angular distribution was measured with 14.9 MeV incident neutrons using the traditional time-of-flight technique with neutron-gamma discrimination. The scattering angle varied from 20o to 65o (laboratory system) in 5o incremental steps. The efficiency of the neutron detectors was measured in the energy range 2–9 MeV relative to the 252Cf-standard, and was calculated using Monte Carlo methods in the 2–14 MeV energy range. Two methods of analysis were applied for experimental and simulated data: a traditional approach with a fixed threshold, and a dynamic threshold approach. The present data agree with the ENDF/B-VII evaluation for the shape of n-p angular distribution within about 1.5%.

A new approach to neutron detector efficiency detemination has been taken. A neutron detector has been calibrated with a 252Cf source at low energy. The calibration can be extended to energies above 8 MeV with accelerator-based neutron sources. This techniques uses the fact that the cross section for a symmetric reaction with nucleus of atomic number A yielding a final nucleus with atomic number (2A−1) and a neutron A+A→(2A−1)+n. This reaction must be symmetric about 90∘ in the center-of-mass system. The laboratory energies for the neutrons at the paired energies differ substantially. Thus, an efficiency known at one of the two angles can be used to determine the efficiency to higher energies or, for a negative Q, to lower neutron energies.

The relative differential cross section for the elastic scattering of neutrons by protons was measured at an incident neutron energy E{sub n}=14.9 MeV and for center-of-mass scattering angles ranging from about 60 deg. to 180 deg. Angular distribution values were obtained from the normalization of the integrated data to the n-p total elastic scattering cross section. Comparisons of the normalized data to the predictions of the Arndt et al. phase-shift analysis, those of the Nijmegen group, and with the ENDF/B-VII.0 evaluation are sensitive to the value of the total elastic scattering cross section used to normalize the data. The results of a fit to a first-order Legendre polynomial expansion are in good agreement in the backward scattering hemisphere with the predictions of the Arndt et al. phase-shift analysis, those of the Nijmegen group, and to a lesser extent, with the ENDF/B-VII.0 evaluation. A fit to a second-order expansion is in better agreement with the ENDF/B-VII.0 evaluation than with the other predictions, in particular when the total elastic scattering cross section given by Arndt et al. and the Nijmegen group is used to normalize the data. A Legendre polynomial fit to the existing n-p scattering data in the 14 MeV energymore » region, excluding the present measurement, showed that a best fit is obtained for a second-order expansion. Furthermore, the Kolmogorov-Smirnov test confirms the general agreement in the backward scattering hemisphere and shows that significant differences between the database and the predictions occur in the angular range between 60 deg. and 120 deg. and below 20 deg. Although there is good overall agreement in the backward scattering hemisphere, more precision small-angle scattering data and a better definition of the total elastic cross section are needed for an accurate determination of the shape and magnitude of the angular distribution.« less

The relative differential cross section for the elastic scattering of neutrons by protons was measured at an incident neutron energy ${E}_{n}=14.9$ MeV and for center-of-mass scattering angles ranging from about ${60}^{\ifmmode^\circ\else\textdegree\fi{}}$ to ${180}^{\ifmmode^\circ\else\textdegree\fi{}}$. Angular distribution values were obtained from the normalization of the integrated data to the $n$-$p$ total elastic scattering cross section. Comparisons of the normalized data to the predictions of the Arndt et al. phase-shift analysis, those of the Nijmegen group, and with the ENDF/B-VII.0 evaluation are sensitive to the value of the total elastic scattering cross section used to normalize the data. The results of a fit to a first-order Legendre polynomial expansion are in good agreement in the backward scattering hemisphere with the predictions of the Arndt et al. phase-shift analysis, those of the Nijmegen group, and to a lesser extent, with the ENDF/B-VII.0 evaluation. A fit to a second-order expansion is in better agreement with the ENDF/B-VII.0 evaluation than with the other predictions, in particular when the total elastic scattering cross section given by Arndt et al. and the Nijmegen group is used to normalize the data. A Legendre polynomial fit to the existing $n$-$p$ scattering data in the 14 MeV energy region, excluding the present measurement, showed that a best fit is obtained for a second-order expansion. Furthermore, the Kolmogorov-Smirnov test confirms the general agreement in the backward scattering hemisphere and shows that significant differences between the database and the predictions occur in the angular range between ${60}^{\ifmmode^\circ\else\textdegree\fi{}}$ and ${120}^{\ifmmode^\circ\else\textdegree\fi{}}$ and below ${20}^{\ifmmode^\circ\else\textdegree\fi{}}$. Although there is good overall agreement in the backward scattering hemisphere, more precision small-angle scattering data and a better definition of the total elastic cross section are needed for an accurate determination of the shape and magnitude of the angular distribution.

The relative differential cross section for the elastic scattering of neutrons by protons was measured at an incident neutron energy E-n = 14.9 MeV and for center-of-mass scattering angles ranging from about 60 degrees to 180 degrees. Angular distribution values were obtained from the normalization of the integrated data to the n-p total elastic scattering cross section. Comparisons of the normalized data to the predictions of the Arndt et al. phase-shift analysis, those of the Nijmegen group, and with the ENDF/B-VII.0 evaluation are sensitive to the value of the total elastic scattering cross section used to normalize the data. The results of a fit to a first-order Legendre polynomial expansion are in good agreement in the backward scattering hemisphere with the predictions of the Arndt et al. phase-shift analysis, those of the Nijmegen group, and to a lesser extent, with the ENDF/B-VII.0 evaluation. A fit to a second-order expansion is in better agreement with the ENDF/B-VII.0 evaluation than with the other predictions, in particular when the total elastic scattering cross section given by Arndt et al. and the Nijmegen group is used to normalize the data. A Legendre polynomial fit to the existing n-p scattering data in the 14 MeV energy region, excluding the present measurement, showed that a best fit is obtained for a second-order expansion. Furthermore, the Kolmogorov-Smirnov test confirms the general agreement in the backward scattering hemisphere and shows that significant differences between the database and the predictions occur in the angular range between 60 degrees and 120 degrees and below 20 degrees. Although there is good overall agreement in the backward scattering hemisphere, more precision small-angle scattering data and a better definition of the total elastic cross section are needed for an accurate determination of the shape and magnitude of the angular distribution.

The reported data are given for the mean angles measured rather than for the central angles. The data are normalized to the most recent Evaluated Nuclear Data File evaluated angle-integrated elastic-scattering cross section and refitted with a Legendre polynomial expansion.

The relative angular distribution of the scattering of neutrons by protons was measured at E-n = 14.9 MeV neutron energy for center-of-mass scattering angles ranging from 60 degrees to 180 degrees. Absolute angular distribution values were obtained by normalizing the measured line shape to the accurately known n-p total cross section. Initial assessment indicates a somewhat better agreement of the data with the predictions of Arndt and Nijmegen than with the ENDF/B-VII.0 evaluation.

We have developed lithium glass detector arrays to measure the energy spectra of neutrons below 1 MeV. The use of a calibrated neutron source spectrum allows measurement of neutron spectra from 0.070 to 14 MeV. The angular distribution and the neutron energy spectra are reported for the Be(d,n) and Be(p,n) neutron source reactions .The applications of these reactions to Boron Neutron Capture Therapy (BNCT) and neutron radiography are discussed.

Relative measurements of the cross section for scattering of neutrons by protons have been made at 10 MeV neutron energy for center-of-mass neutron scattering angles from 60' to 180'. The measurements were made using the Ohio University Accelerator Laboratory's tandem Van de Graaff accelerator with the D(d,n) reaction as the neutron source. The data are in good agreement with predictions from the phase shift analyses of Arndt, the groups of Nijmegen and Bonn, and the ENDF/B-V evaluation. The ENDF/B-VI evaluation does not appear to have the same angular dependence as the data. KEYWORDS: hydrogen cross section, neutron cross section standard, hydrogen angular distribution standard

The relative cross sections for scattering of neutrons by protons have been measured at ${E}_{n}=10 \mathrm{MeV}$ for center-of-mass neutron scattering angles from $60\ifmmode^\circ\else\textdegree\fi{}$ to 180\ifmmode^\circ\else\textdegree\fi{}. Absolute differential cross section values were obtained by normalizing the angle-integrated relative angular distribution to the $n\ensuremath{-}p$ total cross section. The angular distribution exhibits a backward enhancement consistent with an exchange component of the $n\ensuremath{-}p$ interaction at this energy. The relative shape of the angular distribution is in good agreement with the prediction of the charge-dependent Bonn and Nijmegen potential models and with the Arndt phase-shift analysis. Better agreement is found with the evaluated nuclear data files (ENDF)/B-V than with the ENDF/B-VI evaluation.

The level density of {sup 29}Si has been studied over an excitation energy range of 3 to 22 MeV. Three techniques were used to derive level density values from experimental data. In the region of resolved levels, results were obtained from level counting while neutron resonance data were used in the region of slightly overlapping levels near the neutron binding energy. At the highest excitation energies, characterized by strongly overlapping levels, Ericson theory was employed to deduce level densities by examining energy-dependent fluctuations in cross sections. Three reactions yielding the same compound nucleus, {sup 29}Si, were investigated. Partial cross sections from {sup 28}Si(n,p), {sup 28}Si(n,{alpha}), and {sup 27}Al(d,n){sup 28}Si reactions were measured with good experimental resolution and statistical accuracy. From these cross sections, level densities were extracted using the two independent methods proposed by Ericson. Reasonable agreement was found among level densities derived from the two Ericson methods. Values obtained are also fairly consistent with those of various predictions and theoretical models. {copyright} {ital 1997} {ital The American Physical Society}

Alpha-particle production cross sections and spectra produced by neutron bombardment of 59Co are measured at 30, 60, 90, and 135 deg over the neutron energy range from 5 to 50 MeV. A source of neutrons continuous in energy is provided by the Los Alamos Weapons Nuclear Research Facility spallation neutron source facility. Comparison of the measurements with results of calculations including sequential reaction Hauser-Feshbach calculations and pre-equilibrium processes indicates that the majority of the alpha particles result from compound nuclear reactions. The degree of agreement of calculation with experimental data for the cross section as a function of neutron energy and on the alpha-particle emission spectra depends on the selection of nuclear level densities and optical model parameters.