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,
, the first burning stage in helium burning,
is well understood [1], one must also extract the cross section of
the
reaction at the Gamow peak (300 keV)
with high accuracy of approximately 
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.