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Study of nuclei near proton shell closure $Z=82$ is important, as interplay between different shapes has been observed in this region. The proton Fermi level for Tl lies near the $3s_{1/2}$ orbital, but highly shape driving $h_{9/2}$ and $i_{13/2}$ Nilsson orbitals intrude in this region at moderate deformation, the neutron Fermi level also lies near $i_{13/2}$ orbital, above $N=100$. The interplay of these orbitals is responsible to induce different shapes which are manifested in different band structures. The shape of Tl isotopes varies from near spherical in neutron rich $^{202,204}$Tl [1,2] to different deformed structures in neutron deficit Tl isotopes. Triaxial shapes in odd-A and odd-odd isotopes are manifested as Chiral and t-bands in $^{193,194,195,198}$Tl [3,4,5,6]. Magnetic Rotational (MR) bands were observed in $^{194,197}$Tl [7,8]. On the other hand, $^{189,191}$Tl have prolate-oblate shape coexistence [9,10]. However, not much is known for odd-odd $^{190,192}$Tl which seem to be the transitional ones between axial and non-axial shapes in Tl isotopes.
To study the high spin states of $^{190,192}$Tl nuclei, they were populated using the fusion evaporation reaction with $^{30}$Si and $^{16}$O beams from BARC-TIFR Pelletron LINAC facility and K-130 cyclotron at VECC in India, respectively. The INGA setup with up to 17 clover HPGe detectors were used to detect the prompt gamma rays. $\gamma-\gamma$ coincidence relations, DCO ratio and polarization measurements have been used to construct the levelschemes and firm assignments of spin-parity. The levelscheme of $^{190}$Tl have been significantly extended, with the observation and placement of several new $\gamma$-rays, which forms different band structures in this nucleus. An MR band has been identified for the first time in this nucleus [11] and the evidence of a possible chiral band has been observed. In $^{192}$Tl, definite spin-parity and configuration of different bands have been assigned, providing a clear understanding of their underlying structures. Details will be presented in the conference.
This work is supported by Department of Atomic Energy, Govt. of India.
References:
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[11] Snigdha Pal, et al., Eur. Phys. J. A 61, 205 (2025).