Excited states of ${}^{148}$Nd studied via the ${}^{150}$Nd$(p,t){}^{148}$Nd reaction and the observation of possible low-spin two-phonon octupole states at $N=88$

Abstract

We report new data from a ${}^{150}$Nd$(p,t){}^{148}$Nd experiment performed at the John D. Fox Accelerator Laboratory of Florida State University. In total, 54 excited states of ${}^{148}$Nd were observed up to an excitation energy of 3500 keV. In this work, we focus on $0^{+}$ states and their band members. In contrast to previous work, the $0_3^{+}$ band is proposed as the candidate for the two-phonon octupole vibrational band. Supporting $spdf$ IBM-1 calculations are presented. To test the robustness of the IBM calculations, several observables were interrogated and are discussed in this publication. In addition, we make the case that neither the $0_2^{+}$ nor the $0_3^{+}$ states of the other $N=88$ isotones are likely good candidates for two-phonon octupole states. Based on our new data for ${}^{148}$Nd, we propose candidates in ${}^{150}$Sm and ${}^{152}$Gd. Using available $\gamma$-decay data for states with moderate spins in the yrast sequence and a comparison to IBM calculations, we also show how the staggering of the $B(E1)/B(E2)$ ratios in the yrast sequence can possibly be used to probe the appearance of bands with multiple octupole phonons.

Comments: 10 pages, 9 figures, accepted for publication in Physical Review C