Magnesium 23

First direct measurement of the 23Mg(p,γ)24Al reaction

Magnesium 23NovaePeer ReviewedScience

The lowest-energy resonance in the 23Mg(p,γ)24Al reaction, which is dominant at classical nova temperatures, has been measured directly for the first time using the DRAGON recoil spectrometer. The experiment used a radioactive 23Mg beam (mixed within a significantly stronger 23Na beam) of peak intensity 5×107 s-1, at the ISAC facility at TRIUMF. We extract values of ER=485.7-1.8+1.3keV and ωγ=38-15+21 meV from our data (all values in the center-of-mass frame unless otherwise stated). In addition, the experiment prompted a recalculation of the Q value for this reaction based on a revision of the 24Al mass. The effect on the uncertainties in the quantities of ejected 22Na and 26Al from oxygen-neon classical novae is discussed.

Author: Erikson, L. et al.
Journal: Physical Review C

Experimental developments for the study of explosive nucleosynthesis in stars

Aluminium 26Magnesium 23PStellar

For several years now, the -SNS collaboration has been working to place a small neutrino detector at the Spallation Neutron Source at Oak Ridge National Lab. If successful, the experiment may produce the needed neutrino-nucleus cross sections on solid targets such as iron and aluminum. These reaction probabilites are of great interest for a number of reasons, including: neutrino astronomy, explosive nucleosynthesis, and nuclear structure.

However, success for this project requires a very efficient cosmic ray detector to exclude backgrounds. The system would need to be 99% efficient while remaining affordable in a difficult financial climate for basic science. The first half of this thesis addresses a prototype cosmic ray veto based on extruded scintillator with embedded wave-length-shifting fibers. This approach has been successfully used before, and may provide the performance needed for this project. However, our results suggest some additional research and  development would be required to meet the requirements for the -SNS experiment.

The second half of this thesis relates to experimental work to study the resonance strength of the 23Mg(p,)24Al reaction. For this purpose a radioactive ion beam experiment has been conducted at TRIUMF using the DRAGON experiment. This reaction is thought to play an important role during explosive nucleosynthesis such as novae and X-ray bursts. If so, then accurate knowledge of this break-out reaction would help explain the isotopic abundances around that mass range in the universe.

Our results suggest the rate of this reaction at astrophysically relevant energies is lower than predicted and might further exclude explosive binary systems as the production site for such elements as 26Al.

Author: Luke E. Erickson