A new method employing a 12 inch × 12 inch γ-summing single NaI crystal was developed for cross-section measurements of astrophysically relevant capture reactions on medium-mass nuclei. The response function of such a $4\pi$ detector enables the summing of all capture events. As a result, a single peak, the so-called sum peak, arises in the spectra. Its intensity can be used to obtain cross sections of capture reactions with unknown multiplicities. The method enables to first determine these multiplicities, which are then used to derive the corresponding efficiency of the sum peak by means of Monte Carlo simulations. Cross sections are finally obtained from the sum-peak intensity with an average uncertainty of $\approx 15\%$. The method was first applied to the ${}^{62}\mathrm{Ni}$($\alpha ,\gamma$)${}^{66}\mathrm{Zn}$ reaction. The results obtained are in excellent agreement with those reported in literature. The new method proposed here was then employed to determine cross sections of 25 capture reactions in the Ni–Sb region. The cross sections measured for the ${}^{103}\mathrm{Rh}$($p,\gamma$)${}^{104}\mathrm{Pd}$ reaction are also presented. A very good agreement between the cross sections measured in the present work and the corresponding predictions of the Hauser-Feshbach theory was found.

• Received 27 September 2006

DOI:https://doi.org/10.1103/PhysRevC.76.015802