Nuclear structure of light thallium isotopes as deduced from laser spectroscopy on a fast atom beam

Abstract

The neutron-deficient isotopes ' " Tl have been studied using collinear fast atom beam laser spectroscopy with mass-separated beams of 7&(10 to 4&( l0' atoms per second. By laser excitation of the 535 nm atomic transitions of atoms in the beam, the 6s 7s S1&2 and 6s 6p P3/2 hyperfine structures were measured, as were the isotope shifts of the 535 nm transitions. From these, the magnetic dipole moments, spectroscopic quadrupole moments, and isotopic changes in mean-square charge radii were deduced. A large isomer shift in '"Tl was observed, implying a larger deformation in the -, isomer than in the -'+ ground state. The " ' '' 'Tl isotopes have deformations that increase as the mass decreases. A deformed shell model calculation indicates that this increase in deformation can account for the drop in energy of the -' bandhead in these isotopes. An increase in neutron pairing correlations, having opposite and compensating effects on the rotational moment of inertia, maintains the spacing of the levels in the -, strong-coupled band. Results for ' Tl differ from previously published values, but are consistent with the 190, 192Tlm d

Nuclear moments and the change in the mean square charge radius of neutron deficient thallium isotopes

“…In Table 2 we neglect the hfsanomaly and quote the experimental errors. The magnetic moments of the light thallium isotopes have been discussed up to t94T1 in [6] and up to t89T1 in [4]. The present measurements complete the thallium chain to 188T1 as shown in Fig.…”

“…The comparison shows that the deformation values determined by the two methods are of the same order of magnitude but the systematic uncertainties are large both for the fig values from Qo due to the uncertainty in the coupling scheme and in the |/7-fl 2) from IS due to the uncertainty in the slope of the droplet model prediction [30]. Full symbols: this work, other data: [4], [20] The second possibility can be checked by a comparison with recent theoretical calculations by Sagawa et al [31] where explicitly mean changes of rms radii of different nuclear states are given. The calculated change in slope of the isotopical change in radius per neutron pair between the vi13/2 shell and the vp3/2 shell is given to be 0.0224 fm 2.…”

“…The increase of moments and the increase of deviation from the serniempirical values, Qs.e., is due to configuration mixing as discussed in [6]. The spin value 1--6 for the isomeres is excluded [4] and [6] here since the additivity rule yields moments of /~-2.0 n.m. which are in contradiction to the measured ones.…”

“…This value, which does not include Sternheimer corrections, was already used by [4]. For ease of comparison, and because the use of the semiempirical results seems doubtful due to the screening of the valence electrons and configuration mixing [11][12][13], we will adopt this value.…”

“…can be calculated from the known spin, #~ [5] and Afactor of 2~ [4]. With (H(0))=246.1(2)T calculated in that way the magnetic moments of the unstable isotopes can be calculated if the hfs-anomaly A1A42 is neglected.…”