On the C-12 Hoyle state gamma decay

The gamma-decays of C-12 excited levels (the Hoyle state 0(+) at 7.65 MeV and the 9.64 MeV 3(-)) are essential for its production in the universe. We present here a new attempt to precisely measure such gamma-decay probabilities. The measurement was performed at INFN-LNS in Catania using the 4 pi CHIMERA multidetector. In order to measure these low probability decay-channels we performed 4-fold coincidence measurements. The C-12 target nuclei were excited by using a beam of 64 MeV alpha-particles produced by the Superconducting Cyclotron (CS) of INFN-LNS. The scattered alpha-particles and the C-12 recoils were detected and identified by Delta E-E and ToF methods using CHIMERA telescopes. The two emitted gamma -rays in the decay chain were detected and identified by using the second stage of the telescopes, CsI(Tl) scintillators, by means of fast-slow and rise time techniques. Kinematics and energy-momentum conservation laws were used to constrain the data analysis. Also the 3-alpha decay channel probability was measured. Such a simultaneous measurement of all known decay channels was useful to reduce the systematic errors. Preliminary results of the data analysis are reported.