We perform coincidence measurements between α particles and γ rays from a ${}^{233}\mathrm{U}$ source to determine the half-lives of the excited state in a ${}^{229}\mathrm{Th}$ nucleus. We first prove that the half-lives of 42.43- and 164.53-keV states are consistent with literature values, whereas that of the 97.14-keV state [93(7) ps] deviates from a previously measured value [147(12) ps]. The half-lives of 71.83- and 163.25-keV states are determined for the first time. Based on the obtained half-lives and the Alaga rule, we estimate the radiative half-life of the low-energy isomeric state $\left({}^{229m}\mathrm{Th}\right)$ to be $5.0\left(11\right)\times {10}^3$ s, which is one of the key parameters for the frequency standard based on ${}^{229}\mathrm{Th}$.

• Received 1 April 2021
• Accepted 9 July 2021

DOI:https://doi.org/10.1103/PhysRevC.104.024306