Measuring the Radiative Width of the Hoyle State in $^{12}$C

Helium burning is possibly the most important burning phase for stellar nucleosynthesis. The two main products are carbon, produced via the 3$\alpha $ reaction, and oxygen by $^{12}$C($\alpha $,$\gamma )^{16}$O. The 3$\alpha $ reaction represents the start of heavy element production in stars. The fortuitous resonance formed by $^{8}$Be and an alpha particle allows the creation of $^{12}$C$^{\ast }$ (the Hoyle state at 7.65 MeV). Overwhelmingly $^{12}$C$^{\ast }$ decays by emitting an alpha particle, followed by the break up of $^{8}$Be into two alpha particles. Fortunately, there is a small radiative decay branch (approximately 4 x 10$^{-4})$ which allows the excited $^{12}$C$^{\ast }$ nucleus to decay to its ground state. A new measurement of the ratio of the radiative width to the total width has been performed by the Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory STARS/LIBERACE Collaboration. Our current results and experimental method will be presented. This work was sponsored by UC-LLNL under Contract No. W-7405-Eng-48 and Grant Nos. DE-FG-05NA25929, DE-FG52-06NA26206, and DE-FG02-05ER41379.