M. S. Fayache

Effects of the spin-orbit and tensor interactions on M1 excitations in light nuclei

Abstract The effects of varying the spin-orbit and tensor components of a realistic interaction on M1 excitation rates are studied in nuclei in the 0p and 1s-0d shells. Besides the total B(M1) strength also the spin and orbital parts are studied separately. The calculations are self-consistent in that the single-particle energies are obtained with the same interaction that is used between the valence nucleons. For most nuclei (with the possible exception of the upper half of the 1s-0d shell) a much better agreement with the experimental B(M1) rates is achieved by increasing the strength of the spin-orbit interaction relative to the free value. Weakening the tensor interaction relative to the free value in general also improves the comparison with the data, but the effects are less pronounced. Raising the 1s relative to the 0d single-particle level leads to an improved description of energies and B(M1) transition strengths of 1+ states. On a more subtle level, the strength of the spin-orbit interaction in the lower half of the sd shell as determined by the optimum description of M1 excitations leads to a splitting substantially larger than the experimentally observed difference E(J π = 3 2 1 + ) − E(J π = 5 2 1 + ) in 17O but this calculated splitting is in line with the (2l + 1) systematics. Also studied is how much of the M1 orbital and spin strengths lie in an observable region and how much are buried in the grass at higher energies. It is noted that for many nuclei the sum of orbital B(M1) plus the sum of the spin B(M1) strengths is very close to the sum of the total B(M1) strength; thus the summed cross terms are small, although they are not so individually.

Question of low-lying intruder states in 8 Be and neighboring nuclei

The presence of not yet detected intruder states in

Vanishing Gamow-Teller transition rate for A = 14 and the nucleon-nucleon interaction in the medium

^{8}Be

Non-scissors-mode behaviour of isovector magnetic dipole orbital transitions involving isospin transfer

e.g. a

Quadrupole-quadrupole interaction calculations which include N = 2 mixing

J=2^{+}

Orbital and spin magnetic dipole strength in a shell model calculation with ΔN = 2 excitations. 8Be

intruder at 9

The isospin-dependent quadrupole-quadrupole interaction used in shell model calculations – the effects of including ΔN = 2 excitations and a two-body spin-orbit interaction term

MeV

Systematics of the quadrupole-quadrupole interaction and convergence properties

excitation would affect the shape of the

The Question of Low-Lying Intruder States in

\beta ^{\mp }

^8Be

-delayed alpha spectra of