Grant: Subatomic Physics Envelope - Project

Gamma rays from radioactive 22Na produced in stellar events are a highly sought-after target for space-based astronomy missions. Some models of Classical Novae (accretion in a white-dwarf binary system) predict the creation of prolific amounts of 22Na in the ejecta, leading to a potential observable in the characteristic 1.275 MeV gamma ray emitted. This gamma ray would then be a direct test of nova models, and a powerful tool in gamma-ray astronomy. The model predictions depend on the nuclear reaction-rate libraries for all reaction which produce or destroy 22Na in the stellar environment, the destruction of 22Na via radiative proton-capture, 22Na(p,g)23Mg being one of the most important. The value of this rate having a strong influence on the final amount of synthesized 22Na. Recently a new excited state was discovered in 23Mg which will contribute significantly to the reaction rate. This could alter the model predictions by a large amount. An experiment proposal at TRIUMF-ISAC to implant radioactive 22Na targets has already been initiated, resulting in two low-activity targets which are now being tested at the University of Washington, Seattle. We propose to use the intense low-energy proton beam there to measure the strength of the new 22Na(p,g)23Mg resonance directly, providing a new reaction rate for the nova models. An experimental beam-line has already been commissioned at UoW along with a joint TRIUMF-UoW built chamber. The present implanted radioactive targets will be enough to perform initial resonance strength measurements, but in order to complete the experiment we require to implant more targets of higher activity. This proposal is a joint collaboration between the University of Washington Center for Experimental Nuclear Physics and Astrophysics (CENPA) and the DRAGON group at TRIUMF. The DRAGON group are providing essential manpower and expertise to this experiment, lead by myself and Prof Alejandro Garcia of CENPA.