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Excited states in the N ¼ 102 isotones 166 Gd and 164 Sm have been observed following isomeric decay for the first time at RIBF, RIKEN. The half-lives of the isomeric states have been measured to be 950(60) and 600(140) ns for 166 Gd and 164 Sm, respectively. Based on the decay patterns and potential energy surface calculations, including β 6 deformation, a spin and parity of 6 − has been assigned to the isomeric states in both nuclei. Collective observables are discussed in light of the systematics of the region, giving insight into nuclear shape evolution. The decrease in the ground-band energies of 166 Gd and 164 Sm (N ¼ 102) compared to 164 Gd and 162 Sm (N ¼ 100), respectively, presents evidence for the predicted deformed shell closure at N ¼ 100. In the exploration of the nuclear landscape, it is evident that the neutron-rich side of stability contains a vast unknown territory, where approximately half of all the bound nuclides remain to be identified. Furthermore, this is the domain of rapid-neutron-capture (r process) nucleosynthesis, which is poorly understood and yet is key to the creation of chemical elements from iron to uranium (Z ¼ 26-92) in stellar environments [1]. With the advent of the current generation of radioactive-beam facilities, it is now possible to address some of the open questions PRL 113, 262502 (2014) P H Y S I C A L

The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116;120;124 Sn below the neutron separation energy by means of three independent experimental methods. The γ-ray strength functions (GSFs) extracted from primary γ-decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance.

Abstract. Neutron-rich 160,161,162 Sm isotopes have been populated at the RIBF, RIKEN via β decay for the first time. β-coincident γ rays were observed in all three isotopes including γ rays from the isomeric decay of 160