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The neutron-deficient mercury isotopes ($Z=80$) around $N=104$ represent one of the most prominent examples of shape coexistence [1]. This region has been extensively studied using various experimental techniques, such as laser spectroscopy [2,3], decay spectroscopy studies [4,5] and Coulomb excitations [6,7]. These studies point to the coexistence of two classes of states with strong mixing between the low-lying members in $^{182,184}$Hg [1,5-7]. In particular, the presence of $E0$ components in the $I^π \rightarrow I^π$ ($I \neq 0$) transitions has been interpreted as a fingerprint for mixing [1].
In order to study the properties of the low-lying states in mercury isotopes around N=104, the $\beta$ decay of $^{182,184,186}$Tl to excited states in $^{182,184,186}$Hg has been measured at the ISOLDE Decay Station (IDS). The conversion electrons have been measured for the first time at IDS by employing the newly developed SPEDE spectrometer [8], which provided an energy resolution of 7 keV for an electron energy around 250 keV. Compared to the previous study [5], an order of magnitude higher statistics was collected, which resulted in a significant decrease of statistical uncertainties in branching ratios and conversion coefficients.
In $^{182}$Hg the existence of the low-energy 16-keV $2^+_1 \rightarrow 0^+_2$ transition was proven and its strength was determined to be in agreement with the Coulomb excitation study [7]. In addition, other experimental observables such as branching ratios and conversion coefficients, are in a good agreement with the previous measurements [5,7]. The results are compared to the two-state mixing model and a reasonable agreement is obtained.
[1] K. Heyde, J.L. Wood, Rev. Mod. Phys 83, 1467 (2011).
[2] B.A. Marsh et al., Nature Physics 14, 1163 (2018).
[3] S. Sels et al., Phys. Rev. C 99, 044306 (2019).
[4] J. Wauters et al., Phys. Rev. C 50, 2768 (1994).
[5] E. Rapisarda et al., J. Phys. G 44, 074001 (2017).
[6] N. Bree et al., Phys. Rev. Lett 112, 162701 (2014).
[7] K. Wrzosek-Lipska et al., Eur. Phys. J. A 55, 130 (2019).
[8] P. Papadakis et al., Eur. Phys. J. A 54, 42 (2018).