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Radiative decay of the second excited state of C-12

  • Mak, H.B.
  • Evans, H.C.
  • Ewan, G.T.
  • Mcdonald, Arthur B.
  • Alexander, T.K.
Publication Date
Oct 01, 1975
DOI: 10.1103/PhysRevC.12.1158
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The branching ratio ΓradΓ for the electromagnetic decay of the 7.655 MeV second excited state of C12 has been measured by detecting the C12(0.0 MeV) recoils in coincidence with α particles from the C13(He3, α2)C12 (7.655 MeV) reaction at EHe3=4.00 MeV. Coincidence events were identified by means of time-of-flight, energy, and kinematic constraints. Thus, of all the C12 nuclei formed in the second excited state, only those decaying to the C12 ground state by either γ-ray or positron-electron pair emission were selected. Hence the experiment provides a direct measurement of ΓradΓ, where Γrad=Γγ+Γe±, and gives ΓradΓ=(4.15±0.34)×10−4, which is in good agreement with other recent measurements, and suggests that the previously accepted value of ΓradΓ=(2.9±0.3)×10−4 may be too low. The significance of this result is discussed with respect to helium burning rates in stars. NUCLEAR REACTIONS C13(He3, α), E=4.0 MeV; measured α-C12 coin. C12 level deduced ΓradΓ. Enriched target.


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