Level structure andγtransitions inHg202studied by the (n, γ) reaction

Several ($n, \gamma$) techniques at thermal and resonant neutron energies have been used to investigate the level scheme of ${}_{}{}^{202}{}_{}{}^{}\mathrm{Hg}$. Low and high energy ($n, \gamma$) spectra have been measured at the Brookhaven National Laboratory high flux beam reactor using Ge(Li) detectors. Two parameter coincidence spectra and $\gamma -\gamma$ angular correlation data were taken. Primary transitions from resonance capture in ${}_{}{}^{201}{}_{}{}^{}\mathrm{Hg}$ were studied with the fast chopper facility at BNL. The combination of these data led to the construction of a detailed level scheme up to about 2 MeV. Twenty-two excited states were found, most of which could be given spins or spin limits. As in ${}_{}{}^{200}{}_{}{}^{}\mathrm{Hg}$ a systematic behavior of the level population as a function of energy and spin was observed and could be used for spin assignments. Most of the levels, and in particular their $\gamma$ deexcitations, were not accurately known previously. Of special interest is the observation that the lowest excited $0^{+}$ state is at 1564 keV. Another $0^{+}$ state was discovered at 1643 keV. These findings shed new light on the "extra" $0^{+}$ state in ${}_{}{}^{200}{}_{}{}^{}\mathrm{Hg}$ at 1029 keV. The systematics of level energies and branching ratios in the Hg isotopes is treated and is found to be suggestive of significant nuclear structure differences as a function of neutron number. In particular, a comparison with model calculations for core-coupled states revealed extensive disagreements for ${}_{}{}^{202}{}_{}{}^{}\mathrm{Hg}$, in contrast to the rather satisfactory comparison found in ${}_{}{}^{200}{}_{}{}^{}\mathrm{Hg}$.