J. Rekstad

On the recoil term in the particle-rotor model☆

Abstract The recoil term in the particle-rotor model is discussed in some detail. Expressions are given for the recoil term both in the absence and presence of pair correlations. It is concluded that the recoil term cannot be properly absorbed by other parts of the Hamiltonian and thus has to be explicitly evaluated.

An investigation of the Nilsson model potential in the spherical limit: Which values for the potential parameters κ and μ should be used to describe a particular nucleus?

Abstract Shell-model states have been investigated in various regions of the nuclear chart, and single particle level schemes based on the present experimental data from transfer reactions on target nuclei with either N or Z magic are established. These level schemes are used to evaluate the κ- and μ-parameters in the Nilsson model potential. A considerable shift is found in the single particle energies with mass, and it is necessary to allow a large variation in the μ-parameter in order to reproduce this effect. The μ-values deduced for neutron states deviate significantly from the parameters recommended in previous studies. Finally, parameter values to be used with the Nilsson model potential in actual calculations on nuclear properties are proposed.

Particle-rotor model description of the negative-parity states in the transitional 151Sm nucleus

The particle-rotor model has been used to calculate energy levels, spectroscopic factors and B(E2) values in the transitional 151Sm nucleus. Two aspects of the model are emphasized: (i) the recoil term in the particle-rotor Hamiltonian is interpreted as a many-body term and given explicit treatment and (ii) the potential parameters k and μ of the Nilsson potential are determined from the experimental single-particle energies in the spherical limit. The model is capable of giving a consistent description of the observed data.

Studies of single neutron holes in the transitional nuclei N = 83–89:: The 150, 148Nd(d, t) and 150, 148, 146Nd(3He, α) pick-up reactions

Abstract The level structures of the 145, 147, 149 Nd nuclei up to about 5 MeV excitation energy have been investigated with the ( 3 He, α) reaction at 24 MeV. Additional 17 MeV (d, t) data have been obtained for 147, 149 Nd. The angular distributions have been analyzed with standard DWBA calculations, and spectroscopic factors have been deduced. Two groups of states carrying h 11 2 single-particle strength may be associated with the 9 2 − [514] and 11 2 − [505] Nilsson orbitals. A considerable amount of high- l single-particle strength may be found in the continuum observed in the ( 3 He, α) spectra above 3 MeV in all the nuclei.

Studies of single-neutron holes in the transitional nuclei N = 83–89: The 142Ce(d, t)141Ce and 142Ce(3He, α)141Ce pick-up reactions

Abstract The level structure of 141 Ce up to 3.7 MeV excitation energy has been investigated by the (d, t) and ( 3 He, α) reactions using 17 MeV deuteron and 24 MeV 3 He beams respectively. The angular distributions have been analyzed with standard DWBA calculations and spectroscopic factors are deduced. The experimental information is compared to unified model calculations involving both one-particle and two-particle one-hole configurations with quadrupole and octupole vibrations of the underlying N = 82 and N = 84 core.

The 153Sm nucleus: An experimental and theoretical study

Abstract The level structure of 153Sm has been studied by means of the 150Nd(α, n)153Sm reaction. The experiment included measurements of the γ-γ coincidences and γ-ray yield as a function of projectile energy. The rotational band built on the 11 2 − [505] Nilsson orbital was observed up to spin 19 2 , and two ΔI = 2 bands of positive parity were identified with spins up to 19 2 and 21 2 , respectively. These bands are associated with the i 13 2 single-particle structure. The data obtained in the present work together with data available in the literature are compared to the result of a particle-rotor coupling calculation. The 153Sm nucleus is found to be a wellbehaved rotor. An appropriate single-particle level scheme for 153Sm is established.

Angular distributions of protons near resonance for the reaction 12C(d, pγ)13C obtained by shape studies of γ-ray lines

Abstract Angular distributions of protons from the reaction 12 C(d,pγ) 13 C have been obtained from the shape of the Doppler-shifted γ-ray lines. In particular, the 7 keV wide resonance at 1449 keV deuteron energy is studied. The distributions as a function of deuteron energy show interference effects which can be explained only by contributions from at least 4 other resonances, or from a direct reaction. The interference is clearly demonstrated by expressing the angular distributions in terms of Legendre polynomials, and studying the different terms in the distributions as functions of beam energy.

Studies of single-neutron holes in the transitional nuclei N = 83–89: The 148, 150, 152Sm(3He, α) pick-up reactions

Abstract The level structures of the 147, 149, 151 Sm nuclei up to about 5 MeV excitation energy have been investigated by means of the ( 3 He, α) reaction with a 24 MeV 3 He beam. The angular distributions have been analyzed with standard DWBA calculations and spectroscopic factors have been deduced. Two groups of states carrying h 11 2 single-particle strength are associated with the 11 2 − (505) and 9 2 − (514) Nilsson orbitals. A considerable high- l single-particle strength is found in the continuum spectra observed above 3 MeV excitation in all the nuclei.

A study of levels in 141Nd with the (d, t) AND (3He, α) reactions

Abstract The level structure of 141Nd up to 4 MeV excitation has been investigated by the (d, t) and (3He, α) reactions with beams of 17 MeV deuterons and 24 MeV 3He particles. The angular distributions have been analyzed with standard DWBA calculations and spectroscopic factors are deduced. The (lg −1 7 2 ) and 1h −1 11 2 states are severely fragmented in this N= 81 nucleus.

The particle-rotor model with pairing in the s-d shell: An analysis of the 23Na nucleus

Abstract The effect of pair correlations in a particle-rotor model description of s-d shell nuclei has been investigated. The BCS approximation is found to be appropriate provided thata sufficient number of orbitals are included in the pairing calculations. The 23 Na nucleus is studied in detail, and most of the available experimental data can be described within the framework of the particle-rotor model with pairing included.