Nuclear Seminar

¹⁸F(α,p)²¹Ne reaction as an alternative neutron source for r-process in Supernovae

Hye Young Lee
University of Notre Dame

Monday, August 28, 2006   4:00 p.m.   NSH 124
(Refreshments served prior to seminar in NSH 124)

 

Recent observations of the abundance distribution of heavy elements in metal poor old stars suggest an indication of the existence of more than one r-process site, proposing a different site for the synthesis of light r-process nuclei.  This led to a reexamination of previously proposed models for r-process sites which originally did not provide sufficient neutron flux for the production of the very heavy elements.  One of these models is the r-process nucleosynthesis in the supernova shock traveling through the He-rich shell of the pre-supernova star.  In this helium rich environment, a possible neutron source for the second r-process would be the reaction sequence of ¹⁴N(α,γ)¹⁸F(α,p)²¹Ne(α,n)²⁴Mg with rapid depletion of ¹⁴N.  The  statistical model predicted that the ¹⁸F(α,p) reaction can compete with the β⁺-decay at the high densities and temperature in the shock front.  Since ²¹Ne(α,n) has a positive Q-value, it has been identified as a stronger neutron source than ²²Ne(α,n).  The ¹⁸F(α,p)²¹Ne reaction and the inverse reaction ²¹Ne(p,α)¹⁸F have been measured in the energy range of the Gamow window.  Experimental results will be presented and compared with Hauser-Feshbach calculations.  The astrophysical implications of the new reaction rates will be discussed.