The 26gAl(ρ,γ)27Si Reaction at DRAGON

Aluminium 26


The astrophysically important 26gAl(p,γ)27Si radiative proton capture reaction was recently investigated using the ISAC-DRAGON facility at TRIUMF. In this experiment, an intense radioactive 26gAl beam produced at the ISAC radioactive beam facility was used in conjunction with a windowless H2 gas target at the DRAGON facility to investigate narrow resonances which are believed to dominate the rate of this reaction in explosive stellar environments such as novae and supernovae explosions. The 188 keV resonance in 27Si was investigated over a 3 week running period, during which approximately 250 runs were taken. From the data collected, the thick target yield of the reaction will be determined, which will then be used to calculate an experimental value for the resonance strength, a value that can be used in astrophysical models attempting to describe the reactions occurring in explosive stellar nucleosynthesis. The purpose of this project was to work on determining two quantities critical to the calculation of the thick target yield and resonance strength: the normalized beam particles on target over the run, and the BGO gamma array detection efficiency. Two methods of beam normalization were used and refined in the analysis of the experimental runs, and validated one another, showing agreement within 8%. BGO efficiency was evaluated using GEANT simulations for a number of different angular distributions and thresholds, to provide averaged efficiency values. Further work on incorporating angular distributions of emitted gamma radiation into the GEANT simulation is ongoing, and will improve the accuracy of efficiency calculations.

Author: Crawford, H.