Discovery of particle unstable $^{69}$Br

Two-proton capture on $^{68}$Se through $^{69}$Br provides a possible mechanism to bypass the waiting point at $^{68}$Se during explosive hydrogen burning processes on neutron stars. This two-proton capture rate, however, depends exponentially on the $^{69}$Br proton separation energy. We have determined the proton separation energy for $^{69}$Br to be -785+34-40 keV by a direct measurement of the p+$^{68}$Se decay products.\footnote{A M Rogers, W G Lynch, M A Famiano, M S Wallace, F Amorini, D Bazin, R J Charity, F Delaunay, R T de Souza, J Elson, A Gade, D Galaviz, S Hudan, J Lee, S Lobostov, S Lukyanov, M Matos, M Mocko, M B Tsang, D Shapira, L G Sobotka, G Verde, arXiv:1009.2950.}$^,$\footnote{Supported NSF Grant Nos. PHY-0216783, PHY-0606007, PHY-0822648, and PHY-0855013, and DoE Grant Nos. DE-FG02-87ER-40316 and DE-AC02-06CH11357.} This extracted value is less bound than that obtained from Coulomb displacement energy calculations and the known masses for $^{69}$Se and $^{68}$Se. The influence of our value for the proton separation energy for $^{69}$Br on rp-process occurring in Type 1 X-ray bursts is examined in a one-zone burst model.