First identification of a magnetic rotational band in 190Tl

The excited states of 190 Tl nucleus have been studied experimentally by populating them in the fusion-evaporation reaction 165 Ho( 30 Si, 5n) 190 Tl using 157-MeV beam, delivered from the BARC-TIFR pelletron LINAC facility. The de-excited γ γ -rays were detected using the INGA array with 17 Compton-suppressed clover HPGe detectors connected with a digital data acquisition system. A new positive parity band with a sequence of M1 transitions has been observed in 190 Tl and identified as a Magnetic Rotational (MR) band. This band been described under the framework of Semi-Classical Model (SCM). The band is assigned a four quasiparticle configuration π i13/2 π i 13 / 2 ⊗ ⊗ ν (i13/2)⁻¹(p3/2)⁻² ν ( i 13 / 2 ) - 1 ( p 3 / 2 ) - 2 . Shears mechanism with Principal Axis Cranking (SPAC) model calculations have been performed, which well reproduces the experimentally measured B(M1)/B(E2) values. The Total Routhian Surface calculations suggest a small deformation with non-collective alignment of the angular momentum, corresponding to an oblate shape for the band.