The Structure of 12C and Stellar Helium Burning

摘要

The rate of stellar formation of carbon at high temperatures (T3 GK) may increase beyond that which is expected from the Hoyle state at 7.654 MeV due to contributions from higher lying states in ¹²C. The long sought for second 2⁺ state predicted at 9–10 MeV excitation energy in ¹²C was predicted to significantly increase the production of ¹²C. An Optical Readout Time Projection Chamber (O-TPC) operating with the gas mixture of CO₂(80%) + N₂(20%) at 100 Torr with gamma beams from the HIgamma S facility of TUNL at Duke was used to study the formation of carbon (and oxygen) during helium burning. Preliminary measurements were carried out at beam energies: E = 9.51, 9.61, 9.72, 10.00, 10.54, 10.84 and 11.14 MeV. Extra attention was paid to separating the carbon dissociation events, ¹²C(gamma ,3lpha ), from the oxygen dissociation events, ¹⁶O(gamma ,lpha )¹²C. Complete angular distributions were measured giving credence to a newly identified 2⁺ state just below 10.0 MeV.