Identification of a possible proton two-quasiparticle band in ${}^{158}\mathrm{Sm}$

High-spin states in neutron-rich ${}^{158}\mathrm{Sm}$ have been reinvestigated by measuring the prompt $\gamma$ rays emitted in the spontaneous fission of ${}^{252}\mathrm{Cf}$. A new negative-parity band has been established up to spin 12. By comparison with the theoretical calculations, a two-quasiparticle state with $\pi 5/2\left[532\right]$ $\otimes$ $\pi 5/2\left[413\right]$ configuration has been proposed for the band head. The systematics of the two-quasiparticle states and bands in this region are discussed.

Figure 1

The level scheme of ${}^{158}\mathrm{Sm}$ in the present work. Band (2) from Ref. [6] is included for comparison.

Figure 2

Partial $\gamma \text{−}\mathrm{ray}$ coincidence spectrum (a) by gating on 167.5-keV transition in ${}^{158}\mathrm{Sm}$ and 707.1-keV transition in ${}^{90}\mathrm{Kr}$ fission partner, and (b) by gating on 167.5 and 1082.0 keV transitions in ${}^{158}\mathrm{Sm}$ from ${}^{252}\mathrm{Cf}$ SF data. The 212.7-keV transition has a strong contaminated component.

Figure 3

Comparison of the level energies for ${}^{158}\mathrm{Sm}$ with theoretical calculation. The band head energies have been taken as references.