An important aspect for understanding the structure of nuclei far from stability relies on our ability to be able to explain the evolution of collectivity with proton and neutron number. The region that lies just above the Z=50 closed shell in the vicinity of N=Z exhibits interesting collective properties of quadrupole and octupole character.
Octupole correlations in nuclei are generated by the interaction between orbitals of opposite parity near the Fermi surface, which differ by three units of angular momentum. This situation is expected to occur when the number of protons or neutrons is close to 56, 88 and 136. Nuclei in the region with N=Z=56 are very unique since for them octupole correlations are predicted to happen both for protons and neutrons. In this mass region the Fermi surface for both protons and neutrons lies between the d5/2 and the h11/2 orbitals. The strongest octupole collectivity has been predicted for the very light Xe and Ba isotopes with N ≈ Z ≈ 56. Octupole transition probabilities have been determined for the nucleus 114Xe [1], being the deduced B(E3) transition matrix elements for the 3− → 0+ and 5− → 2+ transitions, 77(27) and 68(17) W.u. respectively, i.e., about the largest measured transition moments hitherto.
With the present experiment, we aimed to address specific aspects of the collectivity development when approaching the N=Z line in even lighter Xe isotopes by performing a precise lifetime measurement of the 5- state in 112Xe, which theoretically is expected to present a larger octupole collectivity than 114Xe. In addition, we investigate the quadrupole degree of freedom through the lifetime of the 2+ and 4+ measured for the first time.
The experiment was performed during summer 2018 at the AGATA-NEDA+NW- DIAMANT setup installed at the GANIL laboratory, with the CSNSM “OUPS” plunger device. The 112Xe nuclei was populated in a compound nucleus reaction with a 58Ni beam impinging on a 58Ni 1 mg/cm2 target in the 2 proton 2 neutron evaporation channel.
A 197Au degrader with a thickness of 5 mg/cm2 was installed in the plunger device to degrade the reaction products energy without stopping them, in order to maximize the sensibility.
The detection on at least a neutron in NEDA+NW [2] in coincidence with a g-ray in AGATA [3,4] was used as trigger while the information of DIAMANT will be used off-line for identification of the channels.
In this contribution, we will report on the status of the analysis and preliminary findings.
J.J. Valiente Dobón