New transitions and feeding of the J π = ( 8 + ) isomer in Re 186

The spallation neutron source at the Los Alamos Neutron Science Center Weapons Neutron Research facility was used to populate excited states in Re-186 via (n, 2n gamma) reactions on an enriched Re-187 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 gamma-ray excitation functions for the purpose of identifying. rays by reaction channel. Analysis of the singles gamma-ray spectrum gated on the neutron energy range 10 <= E-n <= 25 MeV resulted in five transitions and one level added to the 186Re level scheme. The additions include the placement of three. rays at 266.7, 381.2, and 647.7 keV which have been identified as feeding the 2.0x10(5) yr, J(pi) = (8(+)) isomer and yield an improved value of 148.2(5) keV for the isomer energy. These transitions may have astrophysical implications related to the use of the Re-Os cosmochronometer.