Low-lying dipole response in the unstable Ni70 nucleus

Le résumé fourni par la source

The Coulomb excitation of the neutron-rich nucleus $^{70}\mathrm{Ni}$ was measured in inverse kinematics at $260A\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ bombarding energy and with a $^{197}\mathrm{Au}$ target. The beam energy allowed us to study the dipole response around the neutron separation energy (up to about 12 MeV). The experiment was performed at the RIKEN Radioactive Isotope Beam Factory (RIBF). The $\ensuremath{\gamma}$ decay from the scattered $^{70}\mathrm{Ni}$ ions at around zero degree was measured with a scintillator detection system composed of large volume ${\mathrm{LaBr}}_{3}$:Ce detectors (${\mathrm{HECTOR}}^{+}$ array) and NaI(Tl) detectors (DALI2 array). Results were obtained for the $E1$ strength in the region where the dipole response is characterized by the presence of the pygmy dipole resonance. The measured $E1$ strength is found to be larger as compared with that of $^{68}\mathrm{Ni}$ below the neutron binding energy. The measured $E1$ strength as a function of energy is compared with available predictions based on relativistic and nonrelativistic approaches, and only in some cases does theory give a reasonable account of the data.

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