$\gamma \gamma$ angular-correlation analysis of ${}^{200}$Hg after cold-neutron capture

We report on a $\gamma \gamma$ angular-correlation experiment investigating ${}^{200}$Hg after cold-neutron capture. The experiment was performed using eight high-purity germanium detectors mounted on an array installed at the PF1B neutron beam line of the research reactor of the Institut Laue-Langevin in Grenoble, France. The geometry of the array allows $\gamma \gamma$ angular-correlation analyses that can be used for the determination of level spins and multipole mixing ratios in ${}^{200}$Hg. We present multipole mixing ratios for secondary $\gamma$ rays and investigate the nature of the ${}^{200}$Hg neutron-capture state by analyzing the observed primary $\gamma$ rays of this nucleus.

Figure 1

Partial level scheme of ${}^{200}$Hg used for the discussion of the multipolarity of the $1225.4$-keV transition depopulating the 1593-keV level. The red branch on the right-hand side shows the newly placed, second component of the 1225-keV doublet. $\gamma$ transition and level energies are given in keV.

Figure 2

(a) A ${\tan }^{-1}\delta$ plot for the $\gamma$-ray cascade $1593\to 368\to 0$ keV. We compare an initial state of spin $J_1=2,1,0$ with our data by varying the multipole mixing ratio $\delta$ of the $1225.4$-keV transition from ${\delta }_1=\tan (-90{}^{\circ })$ to $\tan (+90{}^{\circ })$. The data support the spin $J_1=2$ assignment and are in agreement with ${\delta }_1=-0.09\left(15\right)$. (b) A ${\tan }^{-1}\delta$ plot for the $1254\to 368\to 0$ keV $\gamma$-ray cascade. The global minimum for the spin $J_1=2$ assumption is in agreement with ${\delta }_1=-1.72\left(12\right)$ and is similar to the published multipole mixing ratio for the $1225.4$-keV $1593\to 368$ keV transition in Ref. [19]. The ${\tan }^{-1}\delta$ plot in this figure looks similar to the one shown in Fig. 2 of Ref. [19].

Figure 3

(a) Angular-correlation plot of a cascade including a primary $\gamma$-ray transition $8028\to 1570\to 0$ keV. We compare an initial state of spin $J_1=0$ with one having $J_1=1$. Our experimental values are in very good agreement with the $J_1=0$ assumption. (b) Comparison between a hypothetical $M2$ primary $\gamma$-ray transition in the $0^{-}\to 2^{+}\to 0^{+}$ cascade and the $1^{-}\to 2^{+}\to 0^{+}$ cascade assuming an $E1$ primary $\gamma$ ray. Our data favor the $J_1=1$ hypothesis.