New transitions and feeding of theJπ=(8+)isomer inRe186

Abstract

The spallation neutron source at the Los Alamos Neutron Science Center Weapons Neutron Research facility was used to populate excited states in $^{186}\mathrm{Re}$ via $(n,2n\ensuremath{\gamma})$ reactions on an enriched $^{187}\mathrm{Re}$ target. Gamma rays were detected with the GErmanium Array for Neutron Induced Excitations spectrometer, a Compton-suppressed array of 18 HPGe detectors. Incident neutron energies were determined by the time-of-flight technique and used to obtain $\ensuremath{\gamma}$-ray excitation functions for the purpose of identifying $\ensuremath{\gamma}$ rays by reaction channel. Analysis of the singles $\ensuremath{\gamma}$-ray spectrum gated on the neutron energy range $10\ensuremath{\le}{E}_{n}\ensuremath{\le}25\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ resulted in five transitions and one level added to the $^{186}\mathrm{Re}$ level scheme. The additions include the placement of three $\ensuremath{\gamma}$ rays at 266.7, 381.2, and 647.7 keV which have been identified as feeding the $2.0\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{4pt}{0ex}}\mathrm{yr}$, ${J}^{\ensuremath{\pi}}=({8}^{+})$ isomer and yield an improved value of $148.2(5)\phantom{\rule{4pt}{0ex}}\mathrm{keV}$ for the isomer energy. These transitions may have astrophysical implications related to the use of the Re-Os cosmochronometer.