Revisiting the role of n-p residual interaction and the Newby shift in K = 0 bands in the odd-odd actinides

Abstract.

We present an analysis of all the known $K=0$ bands in the deformed odd-odd actinide nuclei using the two quasiparticle plus rotor model to obtain the values of Newby shift. The Newby shift so obtained is expected to be free from the Coriolis mixing effects. A total of 11 bands of ²³⁸Np, ²³⁴Pa, ^240-244Am and ²⁵⁰Bk have been analyzed. We find that the staggering pattern in all the cases is properly reproduced. We also examine the validity of an empirical rule to obtain the sign of the Newby shift. We find that for the 8 cases when $\Omega_{n} = \Omega_{p} \neq 1/2$, the rule predicts correct sign but the rule does not work in rest of the 3 cases when $\Omega_{n} = \Omega_{p} =1/2$. As an important outcome of our study, we propose the spin parity assignments and level energies of the $K=0$ and $K=5$ G-M partner bands in ²⁴⁰Am, $\{5/2[523]_{p}\otimes 5/2[622]_{n}\}$. We resolve the tentative nature of the assignments and present a unique level scheme. Also, we predict the band-head energy of $K=0$ bands in four cases, namely three $K=0$ bands of ²³⁸Np and one $K=0$ band of ²⁴⁰Am , where the band-head energy is not known experimentally. These results may be useful for future experiments.