Observation of double pygmy resonances in $^{195,196}$Pt and enhanced astrophysical reaction rates

Abstract

Our measurements of $^{195,196}$Pt $γ$-strength functions show a double-humped enhancement in the $E_γ= 4-8$ MeV region. For the first time, the detailed shape of these resonances is revealed for excitation energies in the quasicontinuum. We demonstrate that the corresponding neutron-capture cross sections and astrophysical reaction rates are increased by up to a factor of 2 when these newly observed pygmy resonances are included. These results lend credence to theoretical predictions of enhanced reaction rates due to such pygmy resonances and hence are important for a better understanding of r-process nucleosynthesis.

5 pages, 4 figures