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

Abstract

Several ($n, \ensuremath{\gamma}$) techniques at thermal and resonant neutron energies have been used to investigate the level scheme of $^{202}\mathrm{Hg}$. Low and high energy ($n, \ensuremath{\gamma}$) spectra have been measured at the Brookhaven National Laboratory high flux beam reactor using Ge(Li) detectors. Two parameter coincidence spectra and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$ 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 $^{200}\mathrm{Hg}$.NUCLEAR REACTIONS $^{201}\mathrm{Hg}(n, \ensuremath{\gamma})$, $E=\mathrm{thermal}, 43, 70.9, \mathrm{and} 210$ eV. Measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ $\mathrm{coin}(\ensuremath{\bigominus})$ in $^{202}\mathrm{Hg}$. $^{202}\mathrm{Hg}$ deduced levels, transitions, $J$, $\ensuremath{\pi}$.