Summer report on the 26Al(ρ,γ)Si reaction at DRAGON

Aluminium 26

The 26Al(ρ,γ)27Si reaction has begun at DRAGON, the Detector of Recoils And Gammas Of Nuclear reactions. The experiment is done in inverse kinematics, meaning an aluminum ion produced and accelerated is incident on a hydrogen gas target. The resulting mix of beam ions and 27Si then moves through the DRAGON, which separates the two, allowing silicon recoils to hit the end detectors.

In order to suppress the leaky beam incident of the end detectors, a coincidence measurement is made. For the 26Al(ρ,γ) experiment, however, futher methods of suppression were examined. An ion chamber was used to aid in element separation, and suppression were examined. In order to understand these options, a number of simulations were completed. Also of importance to the experiment was an understanding of the composition of the incoming beam. Certain contaminents of mass 26 were expected to be present in the beam, notably magnesium, sodium and a metastable state of aluminum which would not react in the same way as the ground state. New hardware and analysis was required to look for these contaminents. Also, some programs were written in FORTRAN to aid with the data analysis.

The reaction is of astrophysical interest as 26Al decays via a characteristic gamma-ray which can be readily observed. The 26Al(ρ,γ)27Si reaction is the only direct 26Al destruction process besides β-decay. The reaction rate is currently known to within a factor of four, far from the 20% uncertainties required for consistent astrophysical modelling. Of increasing interest is the extent of 26Al in explosive stellar environments, such as novae and supernovae, environments which the DRAGON facility was made to examine.

In this report, a brief overview of DRAGON will be given, then the results of the various simulations and contamination measurements, and, finally, some preliminary results from the experiment.

Author: Andeson, M.