The Astrophysical $^{187}$Re/$^{187}$Os Ratio: Measurement of the $^{187}$Re(n,2n)$^{186m}$Re Destruction Cross Section

We have continued a program to measure (n,2n) reaction cross sections on $^{187}$Re with an emphasis on population of the $^{186m}$Re isomer with half-life 2 x 10$^{5}$ y. We produced 12 MeV quasi-monoenergetic neutrons with the TUNL Tandem Van de Graaf accelerator and a deuterium gas cell, and we measured the $^{187}$Re(n,b)Y cross sections using activation techniques. While various reaction channels were populated in the activation, our emphasis is on the (n,2n) reaction channels, where $^{186}$Re is populated. Of specific interest is the population of $^{186m}$Re, which has an extremely long lifetime, which complicates the measurement intended. This data is intended to reduce uncertainties in the $^{187}$Re/$^{187}$Os cosmochronometer.