The Coriolis-coupled bands in 231Pa and the decay of 231Th

A re-investigation of the 231Th decay scheme has been performed with magnetic and semiconductor spectrometers. The Q-value of the decay was determined to be Qsub(β)=389+-2keV. For 231Pa the measurements suggest spins and parities of 3/2+, 3/2-, and 5/2-for the 318.0, 320.2, and 351.8 keV levels, respectively. Half-lives of 274+-10 ps and 45.1+-1.3 ns were found for the 58.6keV(7/2-) and the 84.2keV(5/2+) levels. Calculations, in which the Nilsson model was extended to include Coriolis coupling of the isub(13/2) orbitals and two N=4 orbitals, successfully explain the peculiar structure of the positive-parity rotational bands in 231Pa. From these calculations and from the value of the ground state quadrupole moment, derived from the rotational transition probability B(E2,58.6keV), the deformation parameters were determined to be (epsilon 2, epsilon4)=(0.164, -0.100). (Auth.)