The standard $\gamma$-ray energy calibration source ${}^{152}\mathrm{Eu}$ is well known based on the 13.5 y decay of its ground state. However, in addition to this decay ${}^{152}\mathrm{Eu}$ also has two relatively long-lived isomeric states: a 9 h $J^{\pi }=0^{-}$ state at $E^{*}=46$ keV and a 96 min $J^{\pi }=8^{-}$ state at $E^{*}=148$ keV. Here we report a new measurement of the half-lives of both of these isomeric states. Excited states in ${}^{152}\mathrm{Eu}$ were populated following the ${}^{154}\mathrm{Sm}\left(p,3n\right)$ reaction using a 25 MeV proton beam from the K-150 cyclotron at the Cyclotron Institute of Texas A&M University. Post irradiation, $\gamma$ rays from the de-excitation of the long lived isomeric states were measured using the six BGO shielded high-purity germanium (HPGe) clover detectors that are part of the STARLiTeR array. The half-life of the $J^{\pi }=8^{-}$ isomer ${}^{152m_2}\mathrm{Eu}$ was obtained by measuring the decrease in intensity of the 90 keV $\gamma$ ray from the cascade to the ground state. The half-life of this state was measured to be 95.8(4) min which is in agreement with and significantly more precise than the previously measured value of 96(1) min. In a manner similar to the ground state the second long-lived isomer ${}^{151m_1}\mathrm{Eu}$, the $J^{\pi }=0^{-}$ state at 46 keV, $\beta$ decays to excited states in ${}^{152}\mathrm{Gd}$ and ${}^{152}\mathrm{Sm}$. The half-life of this state was measured to be 9.39(7) h using five $\gamma$-ray transitions.

• Received 12 November 2014
• Revised 28 January 2015

DOI:https://doi.org/10.1103/PhysRevC.91.024322