T. Engeland

Core excitation in O18

Abstract The low-lying even-parity energy levels of O 18 are calculated within the shell model. Core excitations from the double closed O 16 system have been taken explicitly into account using the SU 3 coupling scheme. The resulting energy spectrum shows nice agreement with experiments for nearly all states below 6 MeV excitation energy. The branching ratio for the E2 transitions from the first 2 + (1.98 MeV) to the ground state and from the second 0 + (3.63 MeV) to the first 2 + are well described in the calculation even if the absolute values are somewhat too small.

Nuclear structure of light nuclei using the selectivity of high energy transfer reactions with heavy ions

Abstract We present data obtained by bombarding light nuclei with beams of 11B, 12C and 14N at energies of about 10 MeV/nucleon. Reactions involving transfers of various numbers of nucleons were investigated and the spectra of the detected ions correspond to a wide range of excitation energies in the residual nuclei. The results characteristically show only a few strong peaks in each spectrum and the cross sections exhibit many of the features of direct reactions. We explain the apparent high degree of selectivity in terms of the interplay of reaction mechanisms and the structure of the strongly populated states. Firstly, it is shown that a simple semiclassical model of the reaction process indicates that states of the final nucleus with high spin are greatly favoured. On the other hand, it is demonstrated that the shell-model gives a reasonably complete explanation for the occurence of such high spin states at the appropriate excitation energies. These shell-model states are found to be dominated by configuration with the structure of a multi-nucleon cluster, in the ground state of its internal motion, orbiting the core nucleus so that the centre of mass motion of the cluster carries all the excitation quanta.

The weak coupling model applied to the nuclei with A = 16–19: (II). Gamma transitions and spectroscopic factors

Abstract We have formulated particle-hole states according to the weak coupling model where the particle and hole wave functions are respectively eigenfunctions of the particle-particle and hole-hole parts of the Hamiltonian. Previously the energy levels were found to be well given by this model and here we make an extensive comparison between theoretical predictions and experi- mental data on γ-transitions and spectroscopic factors for the nuclei with A = 16–19. Some discrepancies are found, particularly for the 3p-3h states in 16 O, but on the whole the agreement is good and confirms the validity of the weak coupling model.

An application of the weak coupling model to the negative-parity states of the A = 15 nuclei

Abstract The negative-parity states forA = 15 have been investigated in a weak coupling model. Based on particles in the sd shell and holes in the p-shell the final eigenstates are found to be admixtures of Op-1h, 1p-2h Th = 0 and 1p-2h Th = 1 configurations. Good agreement is obtained with the experimental energy levels below 11 MeV. The correspondence between levels in 15N and 15O is discussed.

A weak coupling calculation for the positive parity states of the A = 15 nuclei

Abstract A calculation of the positive parity states for A = 15 has been performed in a weak coupling approach. Based on particles in the sd shell and holes in the p-shell the final eigenstates are found to be admixtures of 1p−2h T h = 0, 1p−2h T h = 1 and 3p−4h configurations. Good agreement is obtained with the experimental energy levels below 10 MeV. In 15 O an additional 5 2 + state is predicted at 8–9 MeV excitation energy. The wave functions are compared with the structure informations obtained from direct reactions. The electromagnetic decay properties are investigated and in most cases we find good agreement with experiment.

Effective interactions and the nuclear shell-model

This review aims at a critical discussion of the interplay between effective interactions derived from various many-body approaches and spectroscopic data extracted from large scale shell-model studies. To achieve this, our many-body scheme starts with the free nucleon-nucleon (NN) interaction, typically modelled on various meson exchanges. The NN interaction is in turn renormalized in order to derive an effective medium dependent interaction. The latter is in turn used in shell-model calculations of selected nuclei. We also describe how to sum up the parquet class of diagrams and present initial uses of the effective interactions in coupled cluster many-body theory.

EFFECTIVE INTERACTIONS AND SHELL MODEL STUDIES OF HEAVY TIN ISOTOPES

Abstract We calculate the low-lying spectra of heavy tin isotopes from A = 120 to A = 130 using the 2s1d0g 7 2 0h 11 2 shell to define the model space. An effective interaction has been derived using 132Sn as closed core employing perturbative many-body techniques. We start from a nucleon-nucleon potential derived from modern meson exchange models. This potential is in turn renormalized for the given medium, 132Sn, yielding the nuclear reaction matrix, which is then used in perturbation theory to obtain the shell model effective interaction.

Extended Shell Model Calculation for even N = 82 Isotones with a Realistic Effective Interaction

Abstract The shell model within the 2s1d0g 7 2 0h 11 2 shell is applied to calculate nuclear structure properties of the even Z = 52−62, N = 82 isotones. The results are compared with experimental data and with the results of a quasiparticle random-phase approximation (QRPA) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the Q -box method whereas for the QRPA the effective interaction is defined by the G-matrix.

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.

Application of realistic effective interactions to the structure of the Zr isotopes

We calculate the low-lying spectra of the zirconium isotopes