Exact shell-model and projected Hartree-Fock calculations for Mg

The results of a projected Hartree-Fock calculation are compared with those of an exact shell-model calculation for states of J ? 6 in the nucleus ²⁴Mg. The realistic Kuo interaction is used, and gives reasonable agreement with experiment.     

A selfconsistent description of 6Li in terms of four-body and two-body substructures

We present some results on the properties of ⁶Li described as 2p-2n and Ip-In substructures whose intrinsic wave functions are determined, in a shell-model basis, as those minimizing the g.s. energy of ⁶Li. The calculation is completely microscopic in the sense that antisymmetrization is fully taken into account and that we start from a bare nucleon-nucleon interaction. Very good agreement with experimental data on the ground state energy and electric form factor is achieved without any adjustable parameter. A relevant result seems to be the large 1s component of our intercluster wave function.     

The reactions 6, 7Li, 9Be, 10B(e,e′p) at 700 MeV and DWIA analysis

The proton spectral functions of ⁶Li, ⁷Li, ⁹Be and ¹⁰B obtained from the (e, e′p) reactions at 700 MeV are presented. The results were analyzed in the distorted-wave impulse approximation, using the shell-model single-particle wave functions consistent with the elastic electron scattering results. The observed Ip proton momentum distributions for the nuclei ⁶Li, ⁷Li and ⁹Be show significant disagreement with the shell-model momentum distributions. The occupation probabilities of the proton single-particle states are around 0.7, with a few exceptions.     

Calculation of nuclear reaction parameters with the generator coordinate method and their interpretation

Collisions between complex nuclei are described variationally in terms of the GCM with the aim of providing evidence that it is a manageable calculational procedure. The variational principle of Kohn and Kato is used to derive the expression for the K-matrix. The space of scattering states is spanned entirely by antisymmetrized products of shell-model wave functions describing separate clusters; the generator coordinate is the separation between the two shell-model potentials. Scattering boundary conditions are enforced by solving an integral equation for the channel GC amplitude in each open channel separately. The main part of evaluation of collision parameters is performed by calculating double integrals of a form factor between channel GC amplitudes. A theorem about a property of the form factors is proved which allows one to reduce the amount of work needed to calculate double integrals.Application of the method to elastic ³H to ⁴He scattering has shown the feasibility of the calculation.It is shown how an analysis of calculated scattering parameters and corresponding scattering states in terms of quasibound states enables one to make a consistent comparison with experiment and to extract some knowledge of the reaction mechanism.Finally a comparative list of the calculational procedures of the GCM and RGM for reactions is made.     

The beta-decay of 8He

A many-level, many-channel R-matrix formula is used to fit the measured ⁸He β-decay data, including the half-life, branching ratios and delayed neutron and triton energy spectra. Satisfactory fits are found with contributions from four 1⁺ levels of ⁸Li, at 0.98, 3.08, 5.15 and 9.06 MeV. The 32 reduced width amplitudes are taken from a shell-model calculation, with only two requiring adjustment. Gamow-Teller matrix elements obtained from the fits are in reasonable agreement with shell-model values.     

Continuum shell-model calculation for Pb

Results of a continuum shell-model calculation of the total photoabsorption cross section for ²⁰⁸Pb are presented and compared with the results of experiments and of bound-state calculations.     

Treatment of continua in the shell-model theory of nuclear reactions

It is shown that by a suitable choice of the bound- and continuum-state functions used to perform shell-model calculations, the continuum-continuum interaction may be minimized. Approximate expressions for the scattering matrix elements are derived that are easily evaluated by simple extensions of the conventional shell-model calculations for bound states. Numerical calculations are performed for neutron scattering from ¹²C within the framework of the deformed rotor model and compared with exact coupled-channel calculations.     

A study of the 91Zr(d,p)92Zr reaction using vector-polarized deuterons

Differential cross sections and vector analyzing powers were measured for the ⁹¹Zr($\text{d}$, d)⁹¹Zr and ⁹¹Zr($\text{d}$, p)⁹²Zr reactions at an incident deuteron energy of 12 MeV. Deuteron optical-model parameters were determined from an analysis of the elastic data. Comparison of the proton data to DWBA predictions showed that the DWBA does not quantitatively reproduce the measured analyzing powers, hence empirical analyzing power calibration curves were required to analyze the data. New spectroscopic information about the configurations of the excited states in ⁹²Zr has been determined and is compared to the results of previous experiments as well as a shell-model calculation. The results of this experiment are in quantitative agreement with the predictions of the shell-model calculation for most of the transitions although some discrepancies do exist.     

Truncation of the nuclear shell-model space using spectral strength distribution

A procedure, based on spectral distribution methods, is introduced to truncate a large shell-model matrix and to renormalize the matrix for the effects of the truncation. The basis states are selected depending on their contribution in the ground-state region and the renormalization is achieved by requiring that the strength distributions of each configuration in the truncated space to have the same widths as those in the full space. The calculation starts with a given effective Hamiltonian in the original space without having to introduce any free parameters due to truncation. Tests against full shell-model calculations in the ds shell are performed for energy levels of ²⁸Si and for electromagnetic transitions in the (ds)⁶T = 0 space.     

The reaction 26Mg(3He,n)28Si at 23 and 45 MeV

Angular distributions of neutron groups from the ²⁶Mg(³He, n)²⁸Si reaction have been measured at bombarding energies of 23.1 and 45.5 MeV. The experimental results are compared with DWBA and coupled-channel calculations. The zero-range DWBA calculation using shell-model two-nucleon spectroscopic amplitudes explains rather well most of the experimental data of the lowest four states in ²⁸Si, but it is necessary to take two-step processes into account to reproduce all of them satisfactorily. A strong neutron group observed at about 6.9 MeV in residual excitation is described as one composed of unresolved four groups, of which three are attributed to positive-parity states in ²⁸Si predicted in this energy region by the shell-model calculation and one to the 6.88 MeV 3⁻ state in ²⁸Si.     

Preliminary spectral distribution study in the lower f—p shell

The spectral distribution method is used to calculate binding energies for elements in the shell-model f—p shell using renormalized Sussex interaction matrix elements appropriate to a ⁴⁰Ca core. Comparison is made between Coulomb corrected empirical values and the results of the above calculation.     

Effects of proton pair vibrations in the low-lying spectrum of closed-shell nuclei: Structure of 48Ca

The importance of proton pair vibrations in the low-lying spectra of closed-shell nuclei with Z ≠ N is emphasized. Indications for the occurrence of these states in ⁴⁸Ca are obtained from a restricted shell-model calculation with both active neutrons and protons.     

On absolute values of α-decay rates

A possible way to remove the discrepancy between calculated and measured α-widths is discussed. The decay rates of ²¹²Po and ²¹⁰Po are computed with the help of shell-model wave functions for parent and daughter nucleus.     

The quasiparticle rpa as a model for gamow-teller ß-decay

The validity of the quasiparticle random-phase approximation is studied by comparing it with full shell-model calculations in the sd-shell. Phenomenological interactions relevant for the sd-shell have been applied, and Gamow-Teller ß⁺ strengths are calculated. It is found that in the QRPA, the ß⁺ strength is a factor of two higher than the shell-model result. The shell-model results are less sensitive to the particle-particle interaction strength than the QRPA. With u, v factors from the shell-model wavefunctions, the ß⁺ strength in the QRPA reproduces the shell-model result. This suggests that the QRPA does not contain enough ground-state correlations.     

Spectroscopy of 47K and proton core-excitations in 48Ca from the 48Ca(t, α)47K reaction

The ⁴⁸Ca(t, α)⁴⁷ K reaction has been measured at 33 MeV bombarding energy. Spectroscopic information has been extracted for 13 states in ⁴⁷K and 9 new levels have been observed in this nucleus. A comparison of Spectroscopic factors is made with a recent shell-model calculation and the presence of proton core-excitations in the ground state of ⁴⁸Ca is examined.     

Beta decay log ft values for transitional odd-mass nuclei

Using the wave functions yielded by the asymmetric rotor model with a decoupled odd nucléon with variable moment of inertia the absolute log ft values for some transitional odd-mass nuclei have been calculated. The dependence on the γ-deformation is important in a few cases. A great improvement is obtained in comparison with a pure spherical shell-model calculation.     

Structure of states and transition rates in the even-even <Emphasis Type="Italic">N</Emphasis> = 82 nucleus <Superscript>136</Superscript>Xe

The properties of the ¹³⁶Xe nucleus are theoretically investigated by using two different approaches: the two-quasiparticle RPA method and the shell-model calculation. The investigated characteristics include both the energy levels and the electromagnetic properties of ¹³⁶Xe. Comprehensive comparison with the experiment that includes all the currently available experimental data is performed.