Refined theoretical values of field and mass isotope shifts in thallium to extract charge radii of Tl isotopes.

Electronic factors for the field and mass isotope shifts in the 6p 2P3/2 → 7s 2S1/2 (535 nm), 6p 2P1/2 → 6d 2D3/2 (277 nm), and 6p 2P1/2 → 7s 2S1/2 (378 nm) transitions in neutral thallium were calculated within the high-order relativistic coupled cluster approach. These factors were used to reinterpret previous experimental isotope shift measurements in terms of charge radii of a wide range of Tl isotopes. Good agreement between theoretical and experimental King-plot parameters was found for the 6p 2P3/2 → 7s 2S1/2 and 6p 2P1/2 → 6d 2D3/2 transitions. It was shown that the value of the specific mass shift factor for the 6p 2P3/2 → 7s 2S1/2 transition is not negligible compared with the value of normal mass shift in contrast to what had been suggested previously. Theoretical uncertainties in the mean square charge radii were estimated. They were substantially reduced compared with the previously ascribed ones and amounted to less than 2.6%. The achieved accuracy paves the way for a more reliable comparison of the charge radii trends in the lead region.

First results on Ge resonant laser photoionization in hollow cathode lamp.

In the framework of the research and development activities of the SPES project regarding the optimization of the radioactive beam production, a dedicated experimental study has been recently started in order to investigate the possibility of in-source ionization of germanium using a set of tunable dye lasers. Germanium is one of the beams to be accelerated by the SPES ISOL facility, which is under construction at Legnaro INFN Laboratories. The three-step, two color ionization schemes have been tested using a Ge hollow cathode lamp. The slow and the fast optogalvanic signals were detected and averaged by an oscilloscope as a proof of the laser ionization inside the lamp. As a result, several wavelength scans across the resonances of ionization schemes were collected with the fast optogalvanic signal. Some comparisons of ionization efficiency for different ionization schemes were made. Furthermore, saturation curves of the first excitation transitions have been obtained. This investigation method and the setup built in the laser laboratory of the SPES project can be applied for the photo-ionization scheme studies also for the other possible radioactive elements.