Speaker
Description
Neutron deficient nuclei in the A=80 mass region present a rich-nuclear structure where subshell effects give rise to sudden shape changes, from highly deformed nuclides in the N≤40 region to spherical isotopes near N=50. Systematics of low-lying states and transitions in neutron-deficient strontium isotopes show a steady reduction in excitation energies and a corresponding increase in reduced transition probabilities as one look to more neutron-deficient isotopes. The reduced transition probability ratio B is found to increase towards the axial rotor limit for more deformed neutron-rich nuclei. A significant deviation from this trend is found for ${}^{82}$Sr [1], with the ratio rising above the vibrational limit, indicating that more complex phenomena is occurring at low excitation energies. Shape coexistence and triaxial degrees of freedom may explain this deviation as both phenomena are common in the A=80 region.
Shape effects in ${}^{82}$Sr have been investigated through the safe multi-step Coulomb excitation using the TIGRESS spectrometer at TRIUMF [2], with the aim of measuring B(E2) and spectroscopic quadrupole moments $Q{}_{s}$. This was done by impinging ${}^{82}$Sr nuclei onto ${}^{196}$Pt and ${}^{208}$Pb targets. The Coulomb excitation code GOSIA [3] was used to extract multiple E2 matrix elements, from which the B(E2) and $Q{}_{s}$ values were determined and, using Kumar-Cline sum rules [4][5], deduced the intrinsic shape invariant quantities, establishing the deformation and axial symmetry of the nucleus. In this presentation, the results of the analysis will be presented and compared with the triaxial rotor empirical model to determine the nuclear axial asymmetry or triaxiality γ [6], and beyond mean-field calculations.
References
1. Evaluated Nuclear Structure Data File (ENSDF), NNDC
2. G. Hackman and C. E. Svensson, Hyperfine Int. 225 (2014) 241
3. D. Cline et al., Gosia User Manual for Simulation and Analysis of Coulomb Excitation Experiments, http://www.pas.rochester.edu/~cline/Gosia/Gosia_Manual_20120510.pdf, Rochester, NY, US, 2012
4. K. Kumar, Phys. Rev. Lett. 28 (1972) 249
5. D. Cline, Ann. Rev. Nucl. Part. Sci. 36 (1972) 249
6. E. A. Lawrie and J. N. Orce, Atom. Data Nucl. Data Tables 164 (2025) 101730