Low energy measurements of the 12C(a,g) reaction with a bubble chamber

Hydrostatic helium burning in stars is dominated be the 3$\alpha$ and the 12C($\alpha,\gamma)$ processes. While the former is thought to be reasonably well understood, the latter has eluded even the most sensitive laboratory measurements. This reaction not only has a strong influence on the nucleosynthesis of most elements of the periodic table, but also determines the structure and evolution of subsequent stellar burning stages and explosive scenarios. We have devised a technique for measuring the 12C($\alpha,\gamma)$ reaction with a considerable improvement in sensitivity from previous experiments. Adopting ideas from dark matter search experiments with bubble chambers, we have found that a superheated water vessel would be sensitive to $\alpha$ particle and 12C recoils produced from a $\gamma$ ray impinging on 16O nuclei. The main advantage of the new target-detector system is a density as high as a factor of 10,000 over conventional gas targets. Also, the detector would be virtually insensitive to the $\gamma$ ray beam itself, thus allowing us to detect only the products of the reaction of interest.