Speaker
Description
The rapid neutron capture process, r-process, is responsible for the production of more than half of the elements heavier than iron. However, the physical conditions and astronomical sites of the r-process have not yet been determined. The lack of experimental data on the properties of the involved exotic nuclei is a significant source of uncertainty. In particular, the difficulty of directly measuring neutron capture reactions for short-lived nuclei hinders the determination of neutron capture rates in the r-process. The area near $^{132}$Sn (Z = 50, N = 82) is a critical region in the r-process. A drastic decrease in the neutron capture rate when crossing the neutron magic number 82 is expected for the compound neutron capture due to the large energy gap after the shell closure. Due to a lack of experimental data, there are large uncertainties in neutron capture rates for this region, which result in large ambiguities in r-process conditions and the calculation of final elemental abundances.
The neutron capture rates can usually be determined with the knowledge of $\gamma$-emission probabilities of the neutron unbound states. However, the low $\gamma$-emission probabilities and usually low $\gamma$-ray detection efficiencies have been experimental obstacles. At the OEDO-SHARAQ beamline in RIKEN RIBF, an alternative method to identify experimental $\gamma$-emission probability was developed, in which the heavy reaction residues are identified with the SHARAQ spectrometer, and the $\gamma$-emission probability can be obtained based on the number of heavy residues with increased neutron numbers. The $^{130}$Sn(d,p) reaction measurement in inverse kinematics was performed using a $^{130}$Sn secondary beam to identify the $\gamma$-emission probabilities in $^{131}$Sn with this method, alongside $^{130}$Te and $^{124}$Sn beams for reference reactions. The kinetic energies of the secondary beams were degraded to about 20 MeV/u. We identified Sn isotopes with A = 129, 130, and 131, which correspond to two, one, and zero neutron emissions after the reaction, respectively, and the $\gamma$-emission probability near the one-neutron separation energy of $^{131}$Sn was explored. Experimental details and preliminary results, including those for the reference isotopes, will be presented.