P.A. Smith

The (3He, n) reaction on tellurium isotopes

Abstract The 122, 124, 125, 126, 128, 130Te(3He, n) reactions have been studied at an incident energy of 25.4 MeV using the University of Colorado 9 m neutron time-of-flight facility. Angular distributions of neutrons have been measured for all targets over the angular range 0°–22°. In addition to the ground state transitions relatively strong L = 0 transitions to excited levels in the region of 2.0 MeV are observed in all residual nuclei. The experimental results are compared to zero-range DWBA predictions. Pairing model calculations are able to account for the strongly excited low-lying Jπ = 0+ states observed.

The (3He, n) reaction on N = 82 targets and even isotopes of neodymium

Abstract Angular distributions of neutrons from the ( 3 He, n) reaction were measured at 25.4 MeV over the angular range 0°–22° for the N = 82 targets 136 Xe, 138 Ba, 139 La, 142 Nd and 144 Sm. In addition, measurements were carried out for the targets 144, 146, 148, 150 Nd spanning the transition from spherical to permanently deformed ground states. For each even A , N = 82 target, transitions to excited states were observed with considerable L = 0 and L = 2 strength. Weak transitions to excited states were observed for the 144 Nd and 139 La targets. Only the ground state transition was observed for the other targets. A careful search was made for the 0 + vibrational states excited in the (t, p) reaction at 0.747 MeV in 150 Sm and 0.686 MeV in 152 Sm, but these were not populated with measurable strength in the ( 3 He, n) reaction. The Q -value for the 144 Sm( 3 He, n) 146 Gd(g.s.) reaction was measured to be 0.977±0.030 MeV, yielding a ground state mass of 145.91832±0.00003 amu for 146 Gd.

A systematic investigation of the (α, 2nγ) reaction on medium-heavy nuclei

Abstract Exclusive neutron spectra and angular distributions have been measured for 28–35 MeV (α, 2nγ) reactions on various nuclei in the 80 ≦ A ≦ 210 region. Pre-equilibrium processes dominate the 35 MeV (α, 2nγ) reaction mechanism in much of this region. Analysis of systematic variation in the neutron spectrum parameters shows that the reaction mechanism is strongly correlated with the target neutron excess parameter ( N − Z / A . Analysis of the γ-decay of the entry states shows that well-defined incident angular momentum windows exist for the pre-etjuilibrium (α, 2nγ) reaction. These features are discussed in terms of various models for the reaction mechanism.

Decay pathways and entry-state population in (α, xnγ) and (3He, xnγ) reactions on 150Nd

Abstract Exclusive neutron spectra and angular distributions have been measured by n-γ coincidence techniques for (α, x n γ) and ( 3 He , x n γ) reactions on 150 Nd in the 25–44 MeV range. The results show that pre-equilibrium processes dominate low-energy light-ion induced reactions at certain beam energies. Analysis of the yrast γ-ray cascades in the residual nuclei shows that a well-defined minimum entry-state spin exists in final nuclei populated by pre-equilibrium processes. This in turn implies the existence of a minimum classical impact parameter for these reactions. These results are discussed in terms of phenomenological models of the reaction mechanisms.

The energy dependence of the 54Fe(p, t) reaction

Abstract Cross sections are presented for the 54 Fe(p, t) 52 Fe reaction studied at 25.2 MeV. These data, along with published data on the same reaction at 45, 51.9 and 80 MeV, have been used to examine the energy dependence of the (p, t) reaction. Single-step distorted-wave calculations carried out both in zero range and exact finite range fail to satisfactorily account for the observed energy dependence. The procedures followed in incorporating a finite range two-nucleon transfer program, calculated in momentum space, into DWUCK5 are outlined.

Semi-microscopic analysis of multi-nucleon transfer and the 40Ca(α, p)43Sc reaction☆

Abstract A semi-microscopic model for analyzing multi-nucleon transfer reactions in the distorted-wave Born approximation is presented. This model, which is shown to be compatible with other semi-microscopic models, employs cluster form factors. The cluster spectroscopic factors are calculated using shell-model wave functions. Data from the 40Ca(α, p)43Sc reaction are presented and used to test the model. The relative cluster spectroscopic factors for a number of levels are found to be in agreement with those calculated using wave functions in an ( f 7 2 ) 3 basis.

The proton shell closure at 14C

Abstract Data for the 14 C( 3 He, d) 15 N and 14 C(t, 4 He) 13 B reactions are compared to DWBA calculations to measure the spectroscopic factors for p 1 2 and p 3 2 proton transitions. Good fits are found for the stripping data, as well as to similar stripping data on 12 C. These results lower the previous value for proton p 3 2 hole strength in 14 C by a factor of two, indicating that the neutron closure of the p-shell has provided a very good proton closed shell at 14 C. Stripping results to low-lying positive parity states in 15 N are interpreted within a Nilsson scheme, which reproduces the experimental results, but which requires a large deformation for the s-d orbitals.

A study of the121,123Sb(p, d) reactions

Levels of120,122Sb have been observed using the121,123Sb(p, d) reactions atEp= 26.2 MeV. Thirty-two levels of120Sb and thirty-four levels of122Sb are observed below 2.0 MeV excitation with an energy resolution better than 25 keV FWHM. Experimental angular distributions were compared to DWBA calculations in order to extractl-transfers and spectroscopic factors. Strong mixing between the 3s1/2, 2d3/2, 2d5/2, and 1g7/2 neutron orbitals is observed in both nuclei. Nuclear Reactions:121,123Sb(p, d),E=26.2 MeV; measuredσ(Ed,θ).120,122Sb deduced levels,l,J,π, spectroscopic factors. Enriched targets, magnetic spectrometer.

A study of the 90Zr(3He, t) reaction at 43.4 MeV

Abstract Low-lying states of 90 Nb have been investigated using the 90 Zr( 3 He, t) reaction at 43.4 MeV. In addition to the well-known π( P 1 2 ) v (g 9 2 ) −1 and π(g 9 2 ) v (g 9 2 ) −1 particle-hole states, many other levels were observed. The angular distributions for the ( g 9 2 ) 2 states are investigated using DWBA calculations using collective, OPEP, and independent tensor and spin-isospin potentials.

A method for determining the neutron multiplicity for gamma rays from (particle, xnγ) reactions

Abstract A technique is presented for identifying γ rays from specific (particle, x n γ ) reactions by measuring the time-of-flight of the outgoing neutrons. Gamma rays associated with different neutron multiplicities are shown to be coincident with different parts of the neutron time-of-flight spectrum.