Many-particle shell model calculation of electromagnetic transition rates and multipole moments in A = 30–34 nuclei

Abstract

Many-particle shell model wavefunctions have been used to calculate magnetic dipole and electric quadrupole transition probabilities and moments as well as log ft values for even-parity states in the A = 30–34 region. The calculations were performed: (i) for bare-nucleon g factors and charges; (ii) for effective g factors and charges obtained from a least-squares fit to experimental data; (iii) for effective single-particle matrix elements obtained from an analogous fit. For the magnetic dipole transitions and moments it appeared necessary to perform separate fits for the A = 30–32 and 33–34 regions. The final best fits for strong transitions are excellent. The average deviation between theory and experiment with three effective single-particle matrix elements for M1 transitions and effective charges for E2 transitions is about 30 %, only slightly larger than the average experimental error. Show cases are 31Si and 33S where the calculated lifetimes, branching ratios and mixing ratios (including the sign) all agree with the measured values within the experimental error. Poor fits, however, are obtained for transitions involving 1 + states and, more generally, states for which the experimental and theoretical spectroscopic factors are in disagreement. Strong M1 transitions generally have a pronounced singe-particle character (with one contribution in the matrix element predominating), whereas all E2 transitions have a collective character (many small contributions).