Electromagnetic transitions in (1f 7/3)±3 nuclei. Mean lives of the low-lying levels of53Mn

The mean lives of three low-lying levels of53Mn at excitation energies of 1.29 MeV (3/2-1), 1.44 MeV (11/2-) and 1.62 MeV (9/2-) have been measured using the Doppler-shift attenuation method with p-γ coincidences in the50Cr(α, pγ)53Mn reaction. The following values have been obtained for the three levels, respectively:τ m =(0.87±0.22), (1.15 ± 0.38) and (0.56 ± 0.15) ps. Branching and multipole mixing ratios in agreement with other recent experimental data have also been obtained. Combining these results we find that M1 transitions between states assumed to belong to the basic (πf 7/3)-3 multiplet are retarded by factors ranging between 50 to 100, while E2 transitions are enhanced by factors of the order of 10. This is in agreement with the behaviour of51V (with (1 f 7/2)3 configuration) supporting the basic shell-model features of nuclei with a48Ca core. © 1972 Società Italiana di Fisica.