Improved Limit on Direct α Decay of the Hoyle State
Abstract
The current evaluation of the triple-α reaction rate assumes that the α decay of the 7.65 MeV, 0+ state in C12, commonly known as the Hoyle state, proceeds sequentially via the ground state of Be8. This assumption is challenged by the recent identification of two direct α-decay branches with a combined branching ratio of 17(5)%. If correct, this would imply a corresponding reduction in the triple-α reaction rate with important astrophysical consequences. We have used the B11(He3,d) reaction to populate the Hoyle state and measured the decay to three α particles in complete kinematics. We find no evidence for direct α-decay branches, and hence our data do not support a revision of the triple-α reaction rate. We obtain an upper limit of 5×10-3 on the direct α decay of the Hoyle state at 95% C.L., which is 1 order of magnitude better than a previous upper limit.
- Publication:
-
Physical Review Letters
- Pub Date:
- May 2012
- DOI:
- 10.1103/PhysRevLett.108.202501
- Bibcode:
- 2012PhRvL.108t2501K
- Keywords:
-
- 23.60.+e;
- 21.60.-n;
- 26.20.Fj;
- 27.20.+n;
- Alpha decay;
- Nuclear structure models and methods;
- Stellar helium burning;
- 6<
- =A<
- =19