Gerald M. Hale

Energy levels of light nuclei A = 4

An evaluation of A = 5-7 was published in Nuclear Physics A708 (2002), p. 3. This version of A = 6 differs from the published version in that we have corrected some errors dis- covered after the article went to press. The introduction an d introductory tables have been omitted from this manuscript. Reference key numbers are in the NNDC/TUNL format.

A consistent set of neutron kerma coefficients from thermal to 150 MeV for biologically important materials

Neutron cross sections for nonelastic and elastic reactions on a range of elements have been evaluated for incident energies up to 150 MeV. These cross sections agree well with experimental cross section data for charged-particle production as well as neutron and photon production. Therefore they can be used to determine kerma coefficients for calculations of energy deposition by neutrons in matter. Methods used to evaluate the neutron cross sections above 20 MeV, using nuclear model calculations and experimental data, are described. Below 20 MeV, the evaluated cross sections from the ENDF/B-VI library are adopted. Comparisons are shown between the evaluated charged-particle production cross sections and measured data. Kerma coefficients are derived from the neutron cross sections, for major isotopes of H, C, N, O, Al, Si, P, Ca, Fe, Cu, W, Pb, and for ICRU-muscle, A-150 tissue-equivalent plastic, and other compounds important for treatment planning and dosimetry. Numerous comparisons are made between our kerma coefficients and experimental kerma coefficient data, to validate our results, and agreement is found to be good. An important quantity in neutron dosimetry is the kerma coefficient ratio of ICRU-muscle to A-150 plastic. When this ratio is calculated from our kerma coefficient data, and averaged over the neutron energy spectra for higher-energy clinical therapy beams [three p (68) + Be beams, and a d (48.5) + Be beam], a value of 0.94 +/- 0.03 is obtained. Kerma ratios for water to A-150 plastic, and carbon to oxygen, are also compared with measurements where available.

S-matrix and R-matrix determination of the low-energy {sup {bold 5}}He and {sup {bold 5}}Li resonance parameters

We study the low-energy 3/2{sup {minus}} and 1/2{sup {minus}} states of {sup 5}He and {sup 5}Li in a microscopic cluster model. The scattering phase shifts of Bond ({alpha}+n) and of Schwandt ({alpha}+p), respectively, are well reproduced. We determine the resonance parameters by localizing the poles of the analytically continued S matrix at complex energies. Our results differ from conventional R-matrix resonance parameters, that were extracted from experimental data using the definition of a resonance based on the positions and widths of reaction cross section peaks. However, they nicely agree with the results of an extended R-matrix method that works at complex energies. {copyright} {ital 1997} {ital The American Physical Society}

Extrapolation of α+ carbon reaction cross sections to astrophysical energies

Abstract R -matrix extrapolations that take into account the effects of subthreshold levels are reported for the α + 12,13 C reaction cross sections. The relatively low extrapolated value S E 1 (300 keV) = 20 keV-b for α + 12 C capture seems compatible with measurements of the β-delayed α-decay spectrum of 16 N, while the extrapolated 13 C( α , n ) 16 O S -factor is found to be nearly two orders of magnitude larger than the Caughlan-Fowler value.

Microscopic calculation of the 4He system

Abstract We report on a consistent, microscopic calculation of the bound and scattering states in the 4He system employing a realistic nucleon-nucleon potential in the framework of the resonating group model (RGM). We present for comparison with these microscopic RGM calculations the results from a charge-independent, Coulomb-corrected R-matrix analysis of all types of data for reactions in the A = 4 system. Comparisons are made between the phase shifts, and with a selection of measurements from each reaction, as well as between the resonance spectra obtained from both calculations. In general, the comparisons are favorable, but distinct differences are observed between the RGM calculations and some of the polarisation data. The partial-wave decomposition of the experimental data produced by the R-matrix analysis shows that these differences can be attributed to just a few S-matrix elements, for which inadequate tensor-force strength in the N - N interaction used appears to be responsible.

An International Evaluation of the Neutron Cross Section Standards

Work is reported here on the process and present results of an international evaluation of the neutron cross section standards. The evaluations include the H(n,n), 3He(n,p), 6Li(n,t), 10B(n,α), 10B(n,α1γ), 197Au(n,γ), 235U(n,f), and 238U(n,f) standard reactions as well as the 238U(n,γ) and 239Pu(n,f) reactions. This evaluation was performed to include new experiments on the standards that have been made since the ENDF/B-VI evaluation was completed and to improve the evaluation process. Evaluations have been completed for the 6Li(n,t), 197Au(n,γ) and 238U(n,γ) cross sections. Also below 20 MeV the H(n,n), 235U(n,f), 238U(n,f) and 239Pu(n,f) cross sections are completed. Many of the cross sections being evaluated are used in neutron dosimetry for fluence determination. The general trend observed for the evaluations is an increase in the cross sections for most of the reactions from fractions of a percent to several percent compared with the ENDF/B-VI results.

The [sup 3]He([rvec d],p)[sup 4 Breve; ]He reaction at low energies

Angular distributions of cross sections and complete sets of analyzing powers for the [sup 3]He([rvec d],p)[sup 4]He reaction have been measured at five energies between E[sub d]=60 and 641 keV. The energy dependence of the cross section was also measured from 245 to 685 keV, and the absolute cross section was determined at E[sub d]=426thinspkeV. The data have been included in an [ital R]-matrix analysis of the [sup 5]Li system. The bare-nuclear cross section derived from the [ital R]-matrix parametrization was used to determine the electron screening potential. [copyright] [ital 1999] [ital The American Physical Society]

He-4 can experiments serve as a database for determining the three-nucleon force?

We report on microscopic calculations for the {sup 4}He compound system in the framework of the resonating group model employing realistic nucleon-nucleon and three-nucleon forces. The resulting scattering phase shifts are compared with those of a comprehensive R-matrix analysis of all data in this system, which are available in numerical form. The agreement between calculation and analysis is very good in most cases. Adding three-nucleon forces yields large effects in many cases. For a few cases, the new agreement is striking. We relate some differences between calculation and analysis to specific data and discuss experiments necessary to clarify the situation. From the results, we conclude that the data of the {sup 4}He system might be well suited to determining the structure of the three-nucleon force.

Microscopic calculation of the spin-dependent neutron scattering lengths on3He

We report on the spin.dependent neutron scattering length on 3He from a microscopic calculation of p-3H, n-3He, and d-2H scattering employing the Argonne v18 nucleon-nucleon potential with and without additional three-nucleon force. The results and that of a comprehensive R-matrix analysis are compared to a recent measurement. The overall agreement for the scattering lengths is quite good. The imaginary parts of the scattering lengths are very sensitive to the inclusion of three-nucleon forces, whereas the real parts are almost insensitive.

R-matrix description of particle energy spectra produced by low-energy 3H + 3H reactions

An