First spectroscopic information from even-even nuclei in the region “southeast” of Sn132 : Neutron-excitation dominance of the 21+ state in

Handing Wang¹,

N. Aoi²,

Satoshi Takeuchi³

et al.

Abstract

The neutron-rich nucleus 132 Cd has been studied at the RIKEN Radioactive Isotope Beam Factory using in-beam γ -ray spectroscopy with two-proton removal reactions from 134 Sn. A γ -ray transition was observed at 618(8) keV and was assigned to the 2 + 1 → 0 + g.s. decay. The 2 + 1 state provides the first spectroscopic information from the even-even nuclei located in the region "southeast" of the doubly magic nucleus 132 Sn. The properties of nuclei with a few valence particles and/or holes outside a doubly magic core are essential for a fundamental understanding of the detailed structure of the atomic nucleus. In particular, exotic nuclei around 132 Sn have received much attention because 132 Sn contains the conventional proton and neutron magic numbers of 50 and 82, respectively, and lies relatively far from the line of β stability. Thus, it provides a key region to explore the possible modification of nuclear structure approaching the neutron drip line. Spectroscopic information from nuclei beyond 132 Sn is, however, very limited owing to difficulties in accessing this exotic region of the nuclear chart on the experimental forefront. Recent experimental results include spectroscopy of the N = 82 isotones located "south" of 132 Sn down to 128 Pd (Z = 46) [1][2][3], and the Z = 50 tin isotopes located in the "east" side up to 138 Sn (N = 88) [4][5][6]. However, experimental information in the "southeast" of 132 Sn is scarce. γ decays from the excited states of the odd-odd nucleus 132 In were reported recently [7]. No spectroscopic study has been performed for even-even nuclei in this region.The present Rapid Communication reports on the identification of the first 2 + state of 132 Cd (Z = 48,N = 84), located "southeast" of 132 Sn (see Fig. 1 measurements of 2 + 1 states for the even-even nuclei closest to 132 Sn in its surrounding quadrant, which is the first such instance among doubly magic nuclei that lie off the line of β stability. Such completeness enables us to investigate the proton and neutron contributions to the excitation.In this region, the 2 + 1 states in even-even nuclei reveal interesting phenomena in their neutron excitations. For the tin isotopes 134,136,138 Sn, the low-lying excited states can be described well by excitations of the valence neutrons outside the 132 Sn core [5,6]. Also, in the "northeast" quadrant, the neutron excitation dominance of the 2 + 1 → 0 + g.s. transition in 136 Te was reported [8] from the reduction in both the 2 + 1 excitation energy [E x (2 + 1 )] and the transition probability [B(E2)] relative to the N = 80 isotope ( 132 Te). Information on the 2 + 1 state is thus crucial for understanding the role of neutrons in the low-lying excitations in this region. It is, therefore, intriguing to extend such studies to the unexplored southeast quadrant, where the nuclei are even more neutron rich, in order to investigate the neutron contributions in the low-lying excitations of these exotic systems.The experiment was carried out at the Radioactive Isotope Beam Factory (RIB...

Observation of a μs isomer in In8549134 : Proton-neutron coupling

“…However, from the experimental point of view, excited states in this region are challenging to access due to low production rates. Indeed, the only reports of characteristic γ rays were presented very recently, emitted from excited states in 132 Cd [8] and 132 In [9]. In the latter case, γ rays allowed the observation of most of the member states of the π 0g −1 9/2 ⊗ ν1 f 7/2 multiplet in 132 In; all of the other expected multiplets in this nucleus remain unobserved.…”