Seminar Details

The Beta-Delayed Proton and Gamma Decay of 27P for Nuclear Astrophysics

Ellen McCleskey, Texas A&M University
Monday, April 22, 12:30 PM - JINA Pizza Lunch
Biomedical & Physical Sciences Bldg., Rm. 1400

The main creation site of 26Al is currently under debate. Recently, Wolf-Rayet stars have been suggested as the main source of 26Al, but contributions from AGB stars, classical novae and core collapse supernovae are also expected. As well as the site, the reactions for its creation or destruction are not completely known. When 26Al is created in novae, the reaction chain is: 24Mg(p,γ)25Al(β+v)25Mg(p,γ)26Al, but this chain can be by-passed by another chain: 25Al(p,γ)26Si(p,γ)27P and it can also be destroyed directly. Another way to by-pass it is through 26mAl(p,γ)27Si* which is dominated by resonant capture. We find and study these resonances by an indirect method, through the β-decay of 27P. A clean and abundant source of 27P was, for the first time, produced and separated with the Momentum Achromat Recoil Spectrometer (MARS) at the Texas A & M Cyclotron Institute. Gamma-rays and β-delayed protons emitted from states above the proton threshold in the daughter nucleus 27Si were measured in order to identify and characterize the resonances. This experiment involved the search for very low energy protons, typically below 200 keV. In silicon detectors, this region is usually dominated by the betabackground. This led to the design of a detector that was less sensitive to the betas but still maintained good energy resolution (10-15 keV FWHM at 200 keV) and the efficiency of the original silicon setup for protons. To meet these requirements, a GEM technique was employed, specifically, a Micro Pattern Gas Amplifier Detector (MPGAD) was used with P10 gas, dubbed the AstroBox. After a series of short test runs, it was found that the beta-background was reduced to around 100 keV and the resolution was approximately 10 keV at 200 keV.