Speaker
Description
A sudden ground-state shape transition is known to occur at $N=60$ for Sr and Zr isotopes, accompanied by dramatic changes in their energy spectra [1]. In contrast, in Mo isotopes with $A\approx100$ the ground-state shape evolution appears to be more gradual, in accordance with the moderate change in $E_x(2_1^+)$ and mean-squared charge radii across $N=60$ [1]. At the same time, the energy of the first excited $0^+$ state in Mo decreases dramatically with increasing neutron number and reaches its minimum in $^{100}$Mo ($N=58$) at 695 keV. The appearance of low-energy $0^+$ states, connected via enhanced E0 transitions, typically implies the presence and mixing of competing configurations characterized by distinct nuclear shapes. Indeed, a recent low-energy Coulomb-excitation study [2] revealed that the triaxial ground state of $^{100}$Mo coexists with a prolate-deformed $0_2^+$ level. However, to this date, little is known about the higher-lying $0^+$ states.
To study the properties of nuclei in this unique region, a $\beta$-decay experiment was carried out at the TRIUMF-ISAC facility. A radioactive ion beam mixture of $^{100}$Rb and $^{100}$Sr was used, and the population of excited states in $A=100$ isotopes ranging from $^{100}$Sr to $^{100}$Mo was observed. The powerful GRIFFIN array [3] coupled to a tape station allowed us to explore the level structure of several nuclei. Within this work, the level scheme of $^{100}$Mo was studied with the aim of observing low-intensity $\gamma$-ray transitions and establishing spins of excited states that have remained undetermined to date.
Results concerning newly discovered structures in $^{100}$Mo will be presented, including a candidate $2^+$ member of a band built on the $0_3^+$ state, hinting at a possible multiple-shape coexistence scenario. Selected finding will be highlighted, including the identification of a new $0^+$ state in $^{100}$Mo via $\gamma$-$\gamma$ angular correlations.
[1] P.E. Garrett et al., Prog. Part. Nucl. Phys. 124 (2022) 103931.
[2] K. Wrzosek-Lipska et al., Phys. Rev. C 86, 064305 (2012).
[3] A.B. Garnsworthy et al., Nucl. Instrum. Methods Phys. Res., Sect. A, 918 (2019).