Nuclear isovector valence-shell excitation of ${}^{202}\mathrm{Hg}$

Excited states of ${}^{202}\mathrm{Hg}$ have been studied via the ${}^{12}\mathrm{C}({}^{202}\mathrm{Hg},{}^{202}\mathrm{Hg}^{*})$ Coulomb excitation reaction at a beam energy of 890 MeV. The $\gamma$-ray transitions from the excited states of ${}^{202}\mathrm{Hg}$ were detected by the Gammasphere array. The intensities of the observed $\gamma$ rays determined the relative populations of the excited states which were used to extract the absolute $M1$ and $E2$ transition strength distributions for excited $2^{+}$ states of ${}^{202}\mathrm{Hg}$ up to 2 MeV. The measured absolute $B(M1;2_7^{+}\to 2_1^{+})$ strength of $0.18\left(8\right){\mu }_{\mathrm{N}}^2$ indicates that the $2_7^{+}$ level of ${}^{202}\mathrm{Hg}$ is the main fragment of the proton-neutron mixed-symmetry $2_{1,\mathrm{ms}}^{+}$ state. Upper limits for the $F$-spin mixing matrix elements of ${}^{202,204}\mathrm{Hg}$ are determined as well.

Figure 1

Doppler-corrected time-background-subtracted $\gamma$-ray spectra after projectile Coulomb excitation on a ${}^{\mathrm{nat}}\mathrm{C}$ target; (a) singles spectrum; (b) spectrum of $\gamma$ rays in coincidence with the $2_1^{+}\to 0_1^{+}$ transition. In both spectra the transitions relevant for this Rapid Communication are highlighted.

Figure 2

Experimental level scheme of ${}^{202}\mathrm{Hg}$ from this Rapid Communication. The thickness of the arrows corresponds to the intensities measured in the present Rapid Communication. The $2_1^{+}\to 0^{+}$ transition intensity is scaled down to fit into the figure. Newly observed transitions and levels are highlighted (red). The transition $2_7^{+}\to 2_1^{+}$ is also highlighted (blue) as the $2_7^{+}$ state is proposed to correspond to the dominant fragment of the $2_{1,\mathrm{ms}}^{+}$ state.

Figure 3

Angular distributions measured for the (a) 1354-, (b) 439-, and (c) 1747-keV transitions. The solid line are fits in (a) and (c) to a sum of Legendre polynomials and in (b) to a constant. The resulting $A_2/A_0$ and $A_4/A_0$ coefficients of the 1354-keV transition are compared to (d) an angular distribution ellipse calculated with the statistical tensor for the $2_7^{+}$ state. The numbers on the ellipse denote the multipole mixing ratio $\delta$ for the $2_7^{+}\to 2_1^{+}$ transition.

Figure 4

$M1$ strength distributions $B(M1;2_{\mathrm{i}}^{+}\to 2_1^{+})$ of (a) ${}^{202}\mathrm{Hg}$ and (b) ${}^{204}\mathrm{Hg}$. Upper limits are illustrated as arrow heads. The $y$ axes are divided into two parts with different scales.

Figure 5

$F$-spin mixing matrix elements $V_{\mathrm{mix}}$ of $N=80$ isotones and $Z=80$ isotopes as a function of $P$ with statistical (color) and systematical error (black).