$\gamma$-ray spectroscopy of ${}^{150}\mathrm{Sm}$ through the $\beta$ decay of ${}^{150}\mathrm{Pm}$ ($T=2.7$ h) and ${}^{150}\mathrm{Eu}^m$ ($T=12.8$ h)

The ${}^{150}\mathrm{Sm}$ nucleus, populated through the $\beta$ decays of ${}^{150}\mathrm{Eu}^m$ and ${}^{150}\mathrm{Pm}$, was investigated by means of $\gamma -\gamma$ coincidence and $\gamma -\gamma$ angular correlation studies using an array of 20 Compton-suppressed Ge detectors. The study particularly focuses on the determination of weakly populated levels and weak decay branches between established levels. A weakly populated state at 1603 keV is established to have spin-parity $0^{+}$ from the angular correlation data; a second weakly populated state at 1786 keV is confirmed to have spin-parity $0^{+}$ on a similar basis.

Figure 1

Scaled down $\gamma$-ray singles spectra from ${}^{150}\mathrm{Pm}$ and ${}^{150}\mathrm{Eu}^m$. The ${}^{150}\mathrm{Eu}^m$ source had several weak impurities, the strongest of which is ${}^{90}\mathrm{Nb}$.

Figure 2

The 334 keV $\gamma$-ray gated $\gamma$-coincidence spectrum for ${}^{150}\mathrm{Pm}$ and ${}^{150}\mathrm{Eu}^m$ illustrating the increased complexity of ${}^{150}\mathrm{Pm}$ due to its higher $Q$ value.

Figure 3

Example $\gamma -\gamma$ angular correlations from ${}^{150}\mathrm{Eu}^m$ supporting the spin zero assignments for the 1603.24 and 1786.54 keV levels. The dashed line is the theoretical value for a 0-2-0 transition (corrected for the angular size of the detector), and the solid line is the best fit of the $a2$ and $a4$ angular correlation parameters to the data.

Figure 4

Determining the experimental value for $\delta$ from the experimental values of $a_2$ and $a_4$ in the 712–334 keV (2-2-0) $\gamma$ cascade. The value of $\delta$ is determined by locating where the $a_2$ and $a_4$ experimental values cross the theory curves at a consistent value of $\delta$. Both experiments yielded consistent results arriving at $\delta =-4.45\left(43\right)$ and $\delta =-4.40\left(27\right)$ for ${}^{150}\mathrm{Eu}^m$ and ${}^{150}\mathrm{Pm}$ respectively. Uncertainties in the experimental values are indicated with the lighter gray bar.

Figure 5

Partial decay scheme of ${}^{150}\mathrm{Sm}$ and the gates supporting the 272.81(4) keV transition between the 1046.15 and 773.37 keV levels.