J. Whalen

Total Neutron Cross Sections of Heavy Nuclei

Total neutron cross sections of the heavy and actinide nuclei /sup 181/Ta, /sup 197/Au, /sup 232/Th, /sup 233/U, /sup 235/U, /sup 238/U, /sup 239/Pu, and /sup 240/Pu were measured from 30 keV to 4.8 MeV. The objective of this work is to provide improved, accurate, and internally consistent total neutron cross-section data in the heavy-element and actinide region and to examine their systematics and nuclear model implications. 34 refs.

Neutron total and scattering cross sections of some even Mo isotopes and the optical model

Abstract Neutron total cross sections of 92 Mo, 96 Mo, 98 Mo and 100 Mo were measured at intervals of ⪅ 10 keV from 1.6 to 5.5 MeV with resolutions of ≈ 10 keV. Neutron elastic and inelastic scattering cross sections of these isotopes were measured from 1.8 to 4.0 MeV at intervals of 0.2 MeV. Neutron groups corresponding to the excitation of forty states were identified. The experimental results were examined in the context of optical and statistical nuclear models. It was concluded that the real part of the optical potential includes a term proportional to [( N -Z)/ A ] and suggested that the imaginary part of the potential was shell dependent with decreasing magnitude as N = 50 is approached. Comparison of measured and calculated inelastic neutron excitation cross sections suggested a number of J π assignments extending previous knowledge.

The optical model of few-MeV neutron elastic scattering from Z = 39 to 51 targets

Abstract Neutron differential-elastic-scattering cross sections of elemental Y, Zr, Nb, Mo, Rh, Pd, Ag, Cd, In, Sn and Sb were measured from ≈ 1.5 to 4.0 MeV, at intervals of ≲ 100 keV, with resolutions of ≈ 50 to 75 keV, and at ten or more scattering angles distributed between 20 and 160°. Complementary broad-resolution neutron total cross sections of elemental Y, Nb Rh, Pd, In, Sn and Sb were measured from ≈ 0.8 to 4.5 MeV at intervals of ≲ 50 keV. The experimental results were interpreted within the framework of the spherical optical-statistical model (OM). A “regional” OM parameter set, quantitatively describing the neutron-nucleus interaction in this mass-energy domain, was deduced from the observed cross sections. Characteristics of this “regional” OM potential are discussed, particularly the geometric, isospin and shell-dependent properties.

Fast-neutron cross sections of the even isotopes of molybdenum

Abstract The neutron total and scattering cross sections of 92 Mo, 94 Mo, 96 Mo, 98 Mo and 100 Mo were experimentally determined. Total neutron cross sections were measured from 0.1 to 1.5 MeV. Neutron elastic and inelastic scattering cross sections were measured from 0.3 to 1.5 MeV. The excitation of states in 94 Mo at 879±10 keV, in 96 Mo at 786±10 and 1161±20 keV, in 98 Mo at 743±10 and 795±10 keV, and in 100 Mo at 520±20, 700±10, 1070±20 and 1147±20 keV was observed. The experimental results were interpreted in the context of the optical-statistical model concepts inclusive of resonance width fluctuation, direct excitation, and isotopie-dependent potential effects and statistically assayed for evidence of intermediate resonance structure.

165Ho fast neutron cross sections

Total neutron cross sections of165 Ho were measured from 0.1 to 1.5 MeV with resolutions of ≲ 2.5 keV. The observed total cross sections varied slowly with energy and displayed no significant structure. Differential neutron elastic and inelastic scattering cross sections were determined at intervals of ≲50keV from 0.3 to 1.5 MeV. The inelastic excitation of states in165Ho at; 98, 214, 371, 460, 517, 586, 712, 824, 995, 1104 and 1143 keV was positively observed with probably identification of several additional states. The observed excited structure and the respective cross sections were correlated with known single-particle and collective states and with excited structure postulated from systematics. The measured cross sections were compared with calculated values based upon spherical and deformed optical-potentials, and compound-nuclear processes. Total cross sections were best described by a spherical potential while the differential elastic angular distributions were better represented by deformed-potential calculations. Resonance interference effects were found small and, at the energies of the present experiments, the contribution of direct processes was not large.

Neutron total, scattering and inelastic Gamma-ray cross sections of yttrium at few MeV energies

Neutron total, scattering and (n; n′,γ) cross sections of elemental yttrium (89Y) were measured in the few-MeV region. The neutron total-cross-section measurements were made with broad resolutions from ≈0.5 to 4.2MeV in steps of ≲0.1 MeV. Neutron elastic- and inelastic-scattering cross sections were measured from ≈1.5 to 4.0 MeV, at incident-neutron energy intervals of ≈50keV and at ten or more scattering angles distributed between 20 and 160 degrees using neutron detection. Inelastic-scattering cross sections were also determined using the (n; n′,γ) reaction at incident energies from 1.6 to 3.8 MeV at intervals of 0.1 MeV. Gamma-rays and/or inelastically-scattered neutrons were observed corresponding to the excitation of levels at: 909.0±0.5, 1,507.4 ±0.3, 1,744.5±0.3, 2,222.6±0.5, 2,530±0.8, 2,566.4±1.0, 2,622.5±1.0, 2,871.9 ±1.5, 2,880.6±2.0, 3,067.0±2.0, 3,107.0±2.0, 3,140.0±2.0, 3,410.0±2.0, 3,450.0±2.0, 3,504.0 ±1.5, 3,514.0±2.0, 3,556.0±2.0, 3,619.0±3.0, 3,629.0±3.0 and 3,715.0±3.0 keV. The experimental results are discussed in terms of the spherical-optical-statistical, coupledchannels, and core-coupling models, and in the context of previously reported excitedlevel structure.

Neutron total and scattering cross sections of 6Li in the low-MeV range☆

Abstract Neutron total cross sections of 6Li are measured at intervals of ≲ 10 keV from ≈ 0.1 to 4.8 MeV with precisions of ≈ 1 to 3 %. Differential elastic scattering cross sections are measured at intervals of ≲ 100 keV from 1.5 to 4.0 MeV at 10 or more scattering angles distributed between ≈ 20 and 160 deg. Differential inelastic scattering cross sections are measured at selected angles in the energy range 3.5 to 4.0 MeV. The experimental results are analyzed in terms of R-matrix theory and the model parameters used to deduce the 6 Li(n ,α) cross sections. The implications of the measurements and their interpretation on the level structure of 7Li and the reaction mechanisms are discussed.

The Interaction of Fast Neutrons with Nickel-60

Neutron total cross sections of /sup 60/Ni were measured with broad resolution from approx. 0.5 to 5.0 MeV at intervals of less than or equal to 50 keV. Differential elastic neutron scattering cross sections were measured from 1.5 to 4.0 MeV at intervals of less than or equal to 50 keV over the scattered neutron angular range from approx. 20 to 160/sup 0/. Differential cross sections for the inelastic neutron excitation of states at 1.342 +- 0.013, 2.168 +- 0.012, 2.304 +- 0.026, 2.509 +- 0.022, 2.636 +- 0.019, and 3.164 +- 0.041 MeV were also measured. The experimental results are interpreted in terms of optical-statistical and coupled-channel models, including consideration of compound nucleus fluctuations and direct-vibrational processes.

Total, scattering and γ-ray-production cross sections for few-MeV neutrons on 54Fe

Abstract Cross sections for the following neutron interactions were obtained for 54 Fe in the few-MeV incident-energy range with resolutions of 50–100 keV: total interaction from ∼0.5 to 4 MeV, elastic scattering from 1.2 to 4 MeV, inelastic scattering from 2 to 4 MeV for excitation energies up to 3 MeV, and inelastic-scattering γ-ray production from 1.4 to 3.6 MeV for transitions corresponding to the deexcitation of levels up to 3 MeV. The results are mutually consistent within experimental errors. A spherical optical-statistical model describes the energy-averaged behavior of these experiments reasonably well, although slight evidence for direct-reaction strength is exhibited by the angular distributions of neutrons scattered to the 1.408 MeV, 2 + , level.

Fast-neutron total and scattering cross sections of58Ni

Neutron total cross sections of58Ni were measured at 25 keV intervals from 0.9 to 4.5 MeV with 50–100 keV resolutions. Attention was given to self-shielding corrections to the observed total cross sections. Differential elastic- and inelastic-scattering cross sections were measured at 50 keV intervals from 1.35 to 4.0 MeV with 50–100 keV resolutions. Inelastic excitation of levels at 1.458±0.009, 2.462+-0.010, 2.791±0.015, 2.927+-0.012 and 3.059+-0.025 MeV was observed. The experimental results were interpreted in terms of optical-statistical and coupled-channels models.