M. T. McEllistrem

The scattering of 8.0 and 9.0 MeV neutrons by 27Al, 28Si, 31P and 32S

Abstract Measurements were made of the differential elastic and inelastic cross sections for neutrons scattered by silicon at 7.71 MeV; and aluminium, silicon, phosphorus and sulphur at 7.97 and 9.05 MeV. Natural scattering samples were used. Finite sample corrections were made for the elastic scattering data. The elastic cross sections have rms relative and absolute uncertainties of 2–5 % and 6–8 % respectively. The inelastic cross sections have rms relative and absolute uncertainties of 3–8 % and 6–10 % respectively. All measured elastic cross sections were compared to theoretical calculations obtained by adding the shape elastic contribution from the optical model to the compound elastic contribution from the statistical model with level-width-fluctuation corrections. Theoretical calculations of the inelastic scattering from the first excited states of 28 Si and 32 S were made by summing the statistical and direct interaction predictions. The measurements agree with the models for 32 S. For 28 Si, only the 9.05 MeV measurements were in agreement with the models. The particle-core coupling model was used to compute the direct interaction contributions to the inelastic cross sections of the low-lying levels of 27 Al and 31 P. These predictions do not adequately describe the inelastic scattering of neutrons by 27 Al and 31 P.

Differential cross sections for (d,α) and (d,t) reactions in Be9

The Be9(d,α)Li7 reaction to the ground and first excited states of Li7 has been studied in the energy range 0.4 MeV≦Ed≦2.4 MeV. The Be9(d, t)Be8 reaction has been studied from 0.86 MeV < Ed < 2.2 MeV. Total cross sections for the Be9(d, p)10 reaction are presented to relate previously published angular distribution data to other Be9+d reactions. The cross sections for the Be9(d,α)Li7 transitions are comparable over the entire energy range and excitation functions for the two transitions show no obvious indication of resonances. Angular distributions for the two transitions are nevertheless dissimilar over the entire energy range. The (d,α) cross sections are observed to be approximately three times as large as the (d, p) cross sections.

Levels of 51V and 55Mn via (n, n′γ) reactions

Abstract Differential cross sections for the production of gamma rays by inelastic neutron scattering in 51 V and 55 Mn have been measured. Gamma-ray branching ratios for the subsequent decay of excited levels have also been obtained. Measurements were made with pulsed-beam techniques for incident neutron energies from 1.0 to 3.1 MeV. Gamma-ray angular distributions and neutron inelastic scattering cross sections are compared with the predictions of the Hauser-Feshbach model. The comparison confirms spin assignments to excited levels of both nuclei. Those assigned are 0.320, 5 2 ; 0.930, 3 2 ; 1.609, 11 2 ; 1.813, 9 2 ; 2.409 ( 3 2 ) in 51 V and 0.126, 7 2 ; 0.983, 9 2 ; 1.289, 11 2 ; 1.527, 3 2 ; 1.884, ( 5 2 , 7 2 ) in 55 Mn. The first number of a pair indicates the excitation energy in MeV and the second the spin. Parentheses indicate tentative assignments. The branching ratios show that E2 transitions dominate in 51 V and M1 transitions dominate in 55 Mn.

Quadrupole moments and nucleon excitation strengths in even-A Sm isotopes

Abstract We present a coherent coupled-channel analysis of 7 MeV neutron and 16 MeV proton elastic and inelastic scattering from 148, 152, 154 Sm. The optical potential and nuclear deformation parameters are determined so as to fit not only these elastic and inelastic scattering data but also the low-energy neutron scattering properties and the total cross sections over a wide energy range. This analysis provides evidence of the same excitation strengths for both projectiles in the case of 152, 154 Sm, and of a smaller excitation strength for the proton than for the neutron in case of 148 Sm. Moreover the quadrupole moments of these deformed optical potentials are in good agreement with those extracted from Coulomb excitation measurements and from nuclear matter distribution calculations.

Threshold effects in the 40Ar(d, p)41Ar reaction☆

Abstract An anomaly attributed to isospin coupling has been observed in the excitation functions of the 40Ar(d, p)41 Ar reaction to the fourth excited level of 41Ar. The anomaly was observed near the threshold of the 40Ar(d, n)41K reaction to the analogue of the 41 Ar level. The position of the (d, n) threshold was measured by observing protons ( p ) from the subsequent decay of 41K. A narrow anomaly is also observed in the excitation functions of the p0 and p2 groups at about the expected threshold energy of the (d, n0) reaction to the ground state analogue, which may be evidence for coupling of other than just analogue channels.

27Al(n, n′γ) reactions and the 3002 keV level

Abstract The neutron inelastic scattering cross sections to the 2980 and 3002 keV levels of 27Al have been seperately determined from the (n, n′γ) reactions to those levels and the known branching ratios for their decay. The cross sections are well reproduced by Hauser-Feshbach formalism calculations. The angular distribution of γ-rays from the 3002 keV level is consistent only with J = 7 2 or 9 2 assinged to the level and supports the recent 9 2 assignment. The excitation energies of observed levels are 843, 1013, 2213, 2730, 2980 and 3002 keV, all ±1 keV.

Erratum: 2 1 + → 0 1 + transition strengths in Sn nuclei [Phys. Rev. C 76 , 021302(R) (2007)]

In our previous work [1], we presented a new lifetime measurement for the 21 state in 112Sn, as determined through the Doppler-shift attenuation method following the (n, n′γ ) reaction [2]. Here, the theoretical F (τ ) value with which one compares the measured F (τ )exp should be modified by an additional term to correct for the recoil velocity distribution when scattering at a neutron energy, En, well above the energy threshold, Elevel [2]. For an angular distribution approximately isotropic in the center of mass, the total F (τ ) is given by

Ground state reorientation effects in elastic scattering cross sections

Abstract Elastic scattering cross sections are shown to be quite sensitive to ground state reorientation amplitudes and cross sections. These effects are dramatically evident when comparing scattering from even-even nuclei with that from high-spin odd- A nuclei, and may affect choices of potentials for odd versus even nuclei. Neutron scattering data from 235 U and 238 U are analyzed via coupled channels methods. The diffraction minima in elastic scattering from 235 U are found to be dominated by reorientation cross sections. The majority of this reorientation is shown to follow from second order virtual nuclear excitations rather than proceeding through amplitudes for direct ground state reorientation.

Fermionic-bosonic couplings in a weakly deformed odd-mass nucleus, {sub 41}{sup 93}Nb

A comprehensive level scheme of {sup 93}Nb below 2 MeV has been constructed from information obtained with the {sup 93}Nb(n,n{prime}{gamma}) and the {sup 94}Zr(p,2n{gamma}{gamma}){sup 93}Nb reactions. Branching ratios, lifetimes, transition multipolarities, and spin assignments have been determined. From M1 and E2 strengths, fermionic-bosonic excitations of isoscalar and isovector characters have been identified from the weak couplings of the {pi}1g{sub 9/2} {circle_times} {sub 40}{sup 92}Zr and {pi}2p{sub 1/2}{sup -1} {circle_times} {sub 42}{sup 94}Mo configurations. A microscopic interpretation of such excitations is obtained from shell-model calculations, which use low-momentum effective interactions.

Study of 0+ States in Deformed Nuclei

In recent 160Gd(p,t) reaction studies the existence of more than ten 0+ states in 158Gd below 3.0 MeV was revealed. We have examined 158Gd with the (n,n′γ) reaction at neutron energies up to 3.5 MeV to confirm the identification of these states and to determine their lifetimes through DSAM measurements. Gamma‐ray excitation function and angular distribution measurements have been performed and γ − γ coincidences have been measured with the KEGS array of detectors. Moderately strong decays are observed from some of these 0+ states.