Electric dipole response of $^{50,52}$Ca

The low-energy electric dipole excitation-mode, sometimes called as pygmy dipole resonance (PDR), located at $6 \sim 10$~MeV was extensively studied. However, its structure is not yet clear. The recent theoretical work showed that the PDR strengths are enhanced at $^{48-54}$Ca [1], and it is due to the occupation of low angular-momentum orbit by the valence neutrons. To investigate the evolution of PDR in these Ca isotopes experimentally, the relativistic Coulomb excitation of $^{50,52}$Ca was performed.

 

 The experiment was performed at RIKEN RIBF. The incoming $^{50,52}$Ca beams were impinged on Pb and C targets. The outgoing charged-particles and neutrons were measured by SAMURAI spectrometer and neutron detectors, respectively. The neutron detectors were the combination of NEBULA and the NeuLAND demonstrator. The de-excitation gamma-ray from the reaction residue was measured by the CsI(Na) array CATANA and LaBr$_3$ detectors.

In this talk, we will report on the dipole response of $^{50,52}$Ca close to the one-neutron separation energy.

 

[1] T. Inakura et al., Phys. Rev. C 84, 021302(R) (2011).