Open Questions in Stellar Helium Burning Studied With (Real and Virtual) Photons

Moshe Gai

Laboratory for Nuclear Sciences, Dept. of Physics, 2152 Hillside Rd. University of Connecticut, Storrs, CT 06269-3046


(gai@uconn.edu, http://www.phys.uconn.edu)

The outcome of helium burning is the formation of the two elements, carbonand oxygen [1,2,3]. The ratio of carbon to oxygen at the end of helium burning is very crucial for understanding the final fate of a progenitor star and the nucleosynthesis of heavy elements in a Type II supernova. While an oxygen rich star is predicted to end up as a black hole, a carbon rich star leads to a neutron star [2]. In addition, Type Ia supernovae are used as standard candles for measuring cosmological distances, and it is essential to understand helium burning, the initial stage of SNIa [4]. Since the triple alpha-particle capture reaction, $^{8}Be(\alpha,\gamma)^{12}C$, the first burning stage in helium burning, is well understood [1], one must also extract the cross section of the $^{12}C(\alpha,\gamma)^{16}O$ reaction at the Gamow peak (300 keV) with high accuracy of approximately $15\%$ or better. This goal has not been achieved [5,6,7], despite repeated strong statements that appeared in the literature. We propose to construct a TPC for use with high intensity photon beams extracted from the HIGS-TUNL facility at Duke University to study the 16o reaction, the time reverse of the 12ag reaction. This work is in progress.