Yrast states of 216Rn and the extent of a region of possible static intrinsic reflection asymmetry.

Abstract

We report the results of a study of the yrast excitation spectrum for $^{216}\mathrm{Rn}$ via the $^{208}\mathrm{Pb}$${(}^{14}$C,\ensuremath{\alpha}2n${)}^{216}$Rn reaction. Measurements of \ensuremath{\gamma}-\ensuremath{\gamma} coincidences, \ensuremath{\gamma}-ray angular distributions, and \ensuremath{\gamma}-x-ray coincidences were made. We propose a level spectrum up to ${J}^{\ensuremath{\pi}}$${=(10}^{+}$) which does not exhibit the alternating parity structure observed in several isotopes of radium and thorium. From an examination of information on $^{216}\mathrm{Rn}$ and the neighboring nuclei, we can tentatively determine that the radon isotopes of masses 216 to 222 and the N=128 isotones $^{216}\mathrm{Ra}$ and $^{218}\mathrm{Th}$ define a lower mass boundary of a region beyond which static intrinsic reflection asymmetric shapes may exist in the nuclear ground states.