High-spin states in ${}^{133}\mathbf{Cs}$ and the shell model description

The high-spin states in ${}^{133}\mathrm{Cs}$, populated using the reaction ${}^{130}\mathrm{Te}({}^7\mathrm{Li},4n)$ with 45-MeV beam energy, have been extended up to an excitation energy of 5.265 MeV using the Indian National Gamma Array. The observed one- and three-quasiparticle bands in ${}^{133}\mathrm{Cs}$, built on the $\pi h_{11/2},\pi g_{7/2}$, $\pi d_{5/2}$; and ${\left(\pi g_{7/2}\pi d_{5/2}\right)}^1\otimes \nu h_{11/2}^{-2}$ configurations, respectively, have similar structure as seen in the lighter odd-$A$ Cs isotopes. The experimental level scheme has been compared with the large-scale shell model calculation without truncation using the $jj55pna$ interaction, showing a good agreement for both positive- and negative-parity states.

Figure 1

Level scheme of ${}^{133}\mathrm{Cs}$. Transitions marked with an asterisk are new.

Figure 2

Spectra obtained by (a) sum of double gates of 191/L and 324/L keV, L depicting the list gate of transitions as shown; (b) double gating on 713/L; and (c) sum of double gates on the transitions shown. The newly observed transitions have been marked with an asterisk.

Figure 3

Spectra obtained by sum of double gates on various transitions.

Figure 4

(a) Evolution of the $5/2^{+}$, $7/2^{+}$, and $11/2^{-}$ bandheads as a function of neutron number for the odd-$A$ ${}^{127-137}\mathrm{Cs}$ isotopes denoted by indices (i)–(vi): (i) ${}^{127}\mathrm{Cs}_{72}$, (ii) ${}^{129}\mathrm{Cs}_{74}$, (iii) ${}^{131}\mathrm{Cs}_{76}$, (iv) ${}^{133}\mathrm{Cs}_{78}$, (v) ${}^{135}\mathrm{Cs}_{80}$, and (vi) ${}^{137}\mathrm{Cs}_{82}$. The bandhead energies and their half-life (wherever known) are also quoted. Comparison is given of the bands built on (b) $5/2^{+}$, (c) $7/2^{+}$, and (d) $11/2^{-}$ states in the same isotopes [3, 8, 21, 22, 23]. The excitation energies corresponding to $J^{\pi }=0^{+}$, $2^{+}$, and $4^{+}$ states of even-$A$ ${}^{126-136}\mathrm{Xe}$ isotopes are shown by red circles.

Figure 5

Evolution of the dipole band as a function of neutron number for the odd-$A$ ${}^{127-133}\mathrm{Cs}$ isotopes denoted by indices (i-iv): (i) ${}^{127}\mathrm{Cs}_{72}$ [8], (ii) ${}^{129}\mathrm{Cs}_{74}$ [24], (iii) ${}^{131}\mathrm{Cs}_{76}$ [22], and (iv) ${}^{133}\mathrm{Cs}_{78}$ (present work).

Figure 6

Comparison between experiment and shell model calculations for the positive-parity yrast, dipole, and negative-parity bands in ${}^{133}\mathrm{Cs}$.

Figure 7

Comparison between experiment (black filled circles) and shell model calculations for the $7/2^{+}$, $11/2^{+}$, and $15/2^{+}$ states of the positive-parity yrast bands in ${}^{133,135,137}\mathrm{Cs}$. There are two expressions for each state: the first expression shows the dominant angular momentum decomposition and the second expression shows the largest wave-function partition corresponding to the dominant angular momentum decomposition. A detailed explanation of these expressions is given in the text.