Lifetime measurement for the isomeric state in ${}^{213}\mathrm{Th}$

The isomeric state in ${}^{213}\mathrm{Th}$ was re-investigated via the reaction ${}^{40}\mathrm{Ar} + {}^{176}\mathrm{Hf}$ at the gas-filled recoil separator Spectrometer for Heavy Atoms and Nuclear Structure. The digital pulse readout technique was employed to record the signals, which enables the feature of dead-time-less data acquisition. Based on the $\mathrm{evaporation}\mathrm{residue}\text{−}\gamma \text{−}\alpha$ correlation analysis, the half-life of $13/2^{+}$ isomer in ${}^{213}\mathrm{Th}$ was measured to be $T_{1/2}=8.30\left(82\right)\mu \mathrm{s}$. The half-life fits in with the systematics of $N=123$ isotones.

Figure 1

(a) Total $\alpha$-particle energy spectrum detected at the focal plane. (b) Two-dimensional plot of the correlation between the $\gamma$ rays and $\alpha$ particles. Maximum searching times for the $\mathrm{ER}\text{−}\gamma$ and $\mathrm{ER}\text{−}\alpha$ pairs are $8\mu \mathrm{s}$ and 0.8 s, respectively.

Figure 2

(a) Delayed $\gamma$ transitions observed within $1.4\mu \mathrm{s}$ after the recoil implants were detected, and the recoil implants were identified by measuring the known $\alpha$ particles from their ground states. (b) and (c) are the same as (a) but the searching time windows were set to be $\mathrm{\Delta }t\left(\mathrm{ER}\text{−}\gamma \right)<8$ and $40\mu \mathrm{s}$, respectively. The $\gamma$ peaks associated with the deexcitation of ${}^{213m}\mathrm{Th}$ are labeled as red stars. The inset of panel (a) shows the level schemes of ${}^{213,214}\mathrm{Th}$ obtained from Ref. [3]. The measured half-life of the isomeric state in ${}^{213}\mathrm{Th}$ deduced from our paper is indicated by the red color.

Figure 3

The fits to the half-life for the isomer in (a) ${}^{213}\mathrm{Th}$, (b) ${}^{214}\mathrm{Th}$, and (c) ${}^{215}\mathrm{Th}$. The data correspond to the sum of the $\gamma$ rays associated with the deexcitation of isomeric states. For further discussions see the text.

Figure 4

Comparison of the decay of isomeric $13/2^{+}$ states in $N=123$ isotones. The indicated half-lives are taken from Ref. [19] for ${}^{207}\mathrm{Po}$, Ref. [20] for ${}^{209}\mathrm{Rn}$, Ref. [21] for ${}^{211}\mathrm{Ra}$, and this paper for ${}^{213}\mathrm{Th}$.