High-spin level scheme of doubly odd ${}^{128}$I

High-spin states in the odd-odd ${}^{128}$I have been studied experimentally using the ${}^{124}$Sn(${}^7$Li, 3n$\gamma$)${}^{128}$I reaction at beam energies of 28 and 32 MeV. A level scheme built on the known $T_{1/2}=175$ ns, ($6^{-})$ isomer has been established. The low-lying states in the level scheme have been proposed to be associated with the $\pi d_{5/2}\otimes \nu h_{11/2}$ and $\pi g_{7/2}\otimes \nu h_{11/2}$ two-quasiparticle excitations. The strongly populated negative-parity states, forming a bandlike structure, have been assigned to be based on the $\pi g_{7/2}\otimes \nu h_{11/2}$ configuration. The $\pi h_{11/2}\otimes \nu h_{11/2}$ multiplet $9^{+}$, ${10}^{+}$, and ${11}^{+}$ members have been identified according to the systematics of the corresponding level structures observed in the lighter odd-odd iodine isotopes. The two-quasiparticle configuration assignments are supported by the nucleon pair approximation and empirical shell-model calculations.

Figure 1

Total projection spectra at 32-MeV (upper panel) and 28-MeV (lower panel) beam energies.

Figure 2

Level scheme of ${}^{128}$I deduced from the present work.

Figure 3

Typical coincidence spectra with gates on the 117.8-, 641.2-, and 239.0-keV transitions. The square denotes transition belonging to ${}^{128}$I but not assigned to the level scheme.

Figure 4

Typical coincidence spectra with gates on the 345.4-, 887.3-, and 402.7-keV transitions. The squares denote transitions belonging to ${}^{128}$I but not assigned to the level scheme.

Figure 5

Low energy $\gamma$-rays detected by the planar detector in coincidence with the 756.5-, 764.7-, and 117.8-keV transitions.

Figure 6

Comparison of experimentally observed low-lying states in ${}^{128}$I with the nucleon pair approximation calculations.

Figure 7

Level spacing systematics for the $\pi g_{7/2}\otimes \nu h_{11/2}$ bands in doubly odd ${}^{122-128}$I (Ref. [34] and present work).

Figure 8

Comparison of the experimental $9^{+}$, ${10}^{+}$, and ${11}^{+}$ members of the $\pi h_{11/2}\otimes \nu h_{11/2}$ multiplet with those calculated by the empirical shell model (SM) and nucleon pair approximation (NPA).

Figure 9

(a) Energy systematics of the ${10}^{+}$ states in doubly odd ${}^{118-128}$I and the $11/2^{-}$ states based on the proton (neutron) $h_{11/2}$ orbital in odd-$Z$ ($N$) ${}^{117-127}$I (${}^{117-127}$Te and ${}^{119-129}$Xe); (b) systematics of level structures and $\gamma$-transition energies in the vicinity of the ${10}^{+}$ states in odd-odd ${}^{124-128}$I. The data are from Refs. [4, 12, 27, 34] and the present work.