Directional Correlation of the Gamma Rays inGd154

Abstract

Directional correlation measurements have been carried out on five cascades involving the gamma rays in ${\mathrm{Gd}}^{154}$. The results of these measurements in conjunction with the work of Juliano and Stephens, and Cork et al, show the existence of two rotational bands and possibly the start of two more such bands. The nature of these bands are explained in terms of the Bohr-Mottelson model for spheroidal nuclei. The levels are characterized by the quantum numbers ($K, I, \pi$) and are listed in order of increasing energy. The ground state rotational band consists of the ground state (0, 0, +) and the first and second excited states of (0, 2, +) and (0, 4, +), respectively. The 0.998-Mev and 1.130-Mev levels are assigned to a second rotational band with $K=2\mathrm{}$ and spin and parity values 2+, 3+, respectively. The assignment of quantum numbers to the 1.400-Mev level can be made as either (2, 2, ±) with the mixture of (99.5±0.25% $D$, 0.5±0.25% $Q$) for the 1.277-Mev gamma ray, or (3, 3, ±) with the mixture of (85±2% $D$, 15±2% $Q$) for the 1.277-Mev gamma ray. The state at 1.723 Mev is best characterized by the quantum numbers (2, 2, -) with the mixture of (99.7±0.3% $E1\mathrm{}$, 0.3±0.3% $M2\mathrm{}$) for the 0.725-Mev gamma ray, or (3, 3, -) with the mixture of (78.5±6% $E1\mathrm{}$, 21.5±6% $M2\mathrm{}$) for the 0.725-Mev gamma ray.