High- K decays and lifetime measurements in 172Hf

Abstract

The known level scheme of 172Hf has been extended with three new collective rotational bands. Many new transitions have also been observed which link the known bands into the lower-spin states, thereby permitting unambiguous spin and parity assignments to be made for the first time. In particular seven low-intensity γ-ray transitions have been established which link the K = 12 intrinsic state into a series of lower- K states. The half-life of the K = 12 state has been determined to be less than 2 ns and reduced hindrance factors have been calculated for each of the new decay transitions. In apparent conflict with the K-selection rule, most of these new decays have small reduced hindrance factors. The reasons for this apparent breakdown in the K-selection rule are discussed in terms of a mixing between states of both low- and high- K. In addition the mean lifetimes of the states in four of the collective rotational bands have been determined using the Doppler shift attenuation method. The deformations extracted from these measurements are in good agreement with predictions from theoretical Total Routhian Surface calculations based on the proposed configuration assignments.