A.B. Smith

Neutron scattering and models: iron

Abstract Differential elastic and inelastic neutron-scattering cross sections of elemental iron are measured from 4.5 to 10 MeV in increments of ≈ 0.5 MeV. The measurements are made at ≳ 40 scattering angles distributed between ≈ 17° and 160°, with emphasis on elastic scattering and inelastic scattering due to excitation of the yrast 2 + state. The measured data is combined with earlier lower-energy results from this laboratory, with recent high-precision ≈ 9.5–15 MeV results from the Physikalisch. Technische Bundesanstalt and with selected values from the literature to provide a detailed neutron-scattering data base extending from ≈ 1.5 to 26 MeV. This data is interpreted in the context of spherical-optical and coupled-channels (vibrational and rotational) models, and the physical implications are discussed. Deformation, coupling, asymmetry and dispersive effects are explored. A good description of the interaction of neutrons with iron is achieved over the energy range ≲ 1.5–26 MeV, avoiding the dichotomy between high- and low-energy interpretations found in previous work in this mass region.

Fast neutron scattering near shell closures: Scandium

Neutron differential elastic- and inelastic-scattering cross sections are measured from approximately=1.5 to 10 MeV with the detail necessary to define the energy-averaged behaviour of the scattering processes. Neutrons corresponding to excitations of 465+or-23, 737+or-20, 1017+or-34, 1251+or-20, 1432+or-23 and 1692+or-25 keV are observed. It is shown that the observables are reasonably described with a conventional optical-statistical model having energy-dependent geometric parameters. These model parameters are consistent with systematic behaviours previously reported from this laboratory. The energy dependencies are alleviated when the model is extended to include the contributions of the dispersion relationship. There is no indication of anomalous behaviour of the neutron interaction with 45Sc, five nucleons from the doubly closed shell at 40Ca.

Fast-neutron scattering at Z = 50: tin☆

Abstract Neutron-elastic- and -inelastic-scattering cross sections of elemental tin were measured from ≈ 1.5 to 10 MeV. Below 3 MeV, ten angular intervals were used distributed between ≈ 20° and 160°, and the incident-energy increments were ≈ 0.1 MeV. From 3 to 4 MeV, 20 angular intervals, distributed over the same angular range, were used, and the energy increments were ≈ 0.2 MeV. From 4.5 to 10 MeV the measurements were made at ⩾ 40 ngular intervals distributed between ≈ 10° and 160°, and at energy increments of ≈ 0.5 MeV. Inelastically scattered neutron groups corresponding to average excitations of ≈ 1.15 and ≈ 2.27 MeV were observed. The exprimental results were combined with elemental and isotopic values from the literature, to form a comprehensive data base extending to 24 MeV for physical interpretations using optical-statistical coupled-channels models, with attention to isospin and collective effects. These physical interpretations were compared with present and previously reported results and with physical concepts.

Fast-neutron interaction with collective cadmium nuclei

Abstract Differential neutron-scattering cross sections of elemental cadmium are measured from ∼ 1.5 to 10 MeV. From ∼ 1.5 to 3.0 MeV the measurements are made at ∼ 100 keV incident-neutron energy intervals and at 10 scattering angles distributed between ≈ 20° and 160°. From 3 to 4 MeV the measurements are made at ∼ 200 keV intervals and 20 angles. Above 4 MeV the interval is ∼ 0.5 MeV with ⩾ 40 differential values at each energy, distributed between ∼ 18° and 160°. Differential cross sections for the excitation of observed “levels” at 0.0 (elastic), 0.589±0.047, 1.291±0.066 and 1.839±0.057 MeV are determined, with attention to the direct excitation of the yrast 2+ levels of the even isotopes, and of the 3 2 + and 5 2 + levels of the odd isotopes. Optical-statistical, dispersive-optical and coupled-channels interpretations are carried out and comparisons made with “global” parameters. Consideration is given to the fundamental nature of the real potential in the vicinity of the Fermi surface with implications on the equation of state and the reduced mass.

Neutron scattering and models: chromium

Neutron elastic-scattering cross sections of elemental chromium are measured from 4.5 - 10 MeV in steps of MeV and at scattering angles distributed between and . Concurrently cross sections for the inelastic neutron-excitation of the yrast (1.434 MeV) level in are determined. The experimental results are combined with lower-energy values previously reported from this group and with results from the literature to form an extensive scattering database which is interpreted in the context of spherical-optical and coupled-channels models. The physical implications of the measurements and models are discussed including; deformation, coupling, dispersive and asymmetry effects.

Neutron scattering from elemental uranium and thorium

Differential neutron-scattering cross sections of elemental uranium and thorium are measured from {approx} 4.5 to 10.0 MeV in steps of {approx} 0.5 MeV. Forty or more differential values are obtained at each incident energy, distributed between {approx} 17{degree} and 160{degree}. Scattered-neutron resolutions are carefully defined to encompass contributions from the first four members of the ground-state rotational band (0{sup 2} g.s., 2{sup +}, 4{sup +} and 6{sup +} states). The experimental results are interpreted in the context of coupled-channels rotational models, and comparisons made with the respective ENDF/B-VI evaluated files. These comparisons suggest some modifications of the ENDF/B-VI {sup 238}U and {sup 232}Th evaluations.

Neutron interaction with doubly-magic 40Ca

Abstract Differential neutron elastic- and inelastic-scattering cross sections of elemental calcium are measured from ≈ 1.5 to 10 MeV with sufficient detail to determine their energy-averaged behavior in the highly fluctuating environment. These results, combined with values previously reported in the literature, are assessed in the contexts of optical-statistical, dispersive-optical, and coupled-channels models, applicable to the energy domain 0–30 + MeV, with particular emphasis on the lower energies where the processes are sensitive to the dispersion relationship. The interpretations define the energy dependencies of the potential parameters (resolving prior ambiguities), suggest that previous estimates of the prominent low-energy (n, p) and (n, α) reactions are too large, reasonably describe observables to at least 30 MeV, and provide a vehicle for extrapolation into the bound-state regime that gives a good description of hole- and particle-state binding energies. The resulting real-potential parameters are consistent with global trends.

Fast-neutron scattering from vibrational palladium nuclei

Abstract Differential neutron elastic-scattering cross sections are measured from ≈ 1.5 to 10 MeV in sufficient energy and angle detail to define the energy-average behavior. Concurrently, neutron inelastic-scattering cross sections are measured from ≈ 1.5 to 8 MeV. Inelastically-scattered neutron groups are observed corresponding to excitations of: 306 ± 14, 411 ± 47, ≈ 494, 791 ± 20, 924 ± 20, 1156 ± 24, 1358 ± 35, 1554 ± 47 and 1706 ± 59 keV, with additional tentative groups at 1938 and 2059 keV. Particular attention is given to the inelastic excitation of the 2+ yrast states of the even isotopes. This broad data base is examined in the context of optical-statistical and coupled-channels models. The resulting model parameters are consistent with systematic trends in this vibrational mass region and provide a suitable vehicle for many applications.

Elemental ABAREX -- a user's manual.

ELEMENTAL ABAREX is an extended version of the spherical optical-statistical model code ABAREX, designed for the interpretation of neutron interactions with elemental targets consisting of up to ten isotopes. The contributions from each of the isotopes of the element are explicitly dealt with, and combined for comparison with the elemental observables. Calculations and statistical fitting of experimental data are considered. The code is written in FORTRAN-77 and arranged for use on the IBM-compatible personal computer (PC), but it should operate effectively on a number of other systems, particularly VAX/VMS and IBM work stations. Effort is taken to make the code user friendly. With this document a reasonably skilled individual should become fluent with the use of the code in a brief period of time.

Neutron scattering and models: Titanium

Differential neutron elastic-scattering cross sections of elemental titanium were measured from 4.5 {r_arrow} 10.0 MeV in incident energy increments of {approx} 0.5 MeV. At each energy the measurements were made at forty or more scattering angles distributed between {approx} 17 and 160{degree}. Concurrently, differential neutron inelastic-scattering cross sections were measured for observed excitations of 0.975 {+-} 0.034, 1.497 {+-} 0.033, 2.322 {+-} 0.058, 3.252 {+-} 0.043, 3.700 {+-} 0.093, 4.317 {+-} 0.075 and 4.795 {+-} 0.100 MeV. All of the observed inelastically-scattered neutron groups were composites of contributions from several isotopes and/or levels. The experimental results were used to develop energy-average optical, statistical and coupled-channels models.