Lifetimes of the Low-EnergyM1Transitions inLa137andKr83

Abstract

Using conventional time to pulse-height techniques, the lifetimes of the low-lying levels in ${\mathrm{La}}^{137}$ and ${\mathrm{Kr}}^{83}$ have been measured, despite the low $\gamma$-ray energies (10 and 9.3 keV) and the large internal conversion coefficients (130 and 11). The results of 89±4 and 147±4 nsec, respectively, correspond to retardation factors of 370 and 45 over the single-particle model predictions for those $M1\mathrm{}$ transitions.