In-source laser spectroscopy of polonium isotopes: From atomic physics to nuclear structure

The Resonance Ionization Laser Ion Source RILIS [1] at the CERN-ISOLDE on-line radioactive ion beam facility is essential for ion beam production for the majority of experiments, but it is also powerful tool for laser spectroscopy of rare isotopes. A series of experiments on in-source laser spectroscopy of polonium isotopes [2, 3] revealed the nuclear ground state properties of 191;211;216;218Po. However, limitations caused by the isobaric background of surface-ionized francium isotopes hindered the study of several neutron rich polonium isotopes. The development of the Laser Ion Source and Trap (LIST) [4] and finally its integration at ISOLDE has led to a dramatic suppression of surface ions. Meanwhile, the RILIS laser spectroscopy capabilities have advanced tremendously. Widely tunable titanium:sapphire (Ti:Sa) lasers were installed to complement the established dye laser system. Along with a new data acquisition system [5], this more versatile laser setup enabled rst ever laser spectroscopy of the radioactive element astatine [6]. Narrow bandwidth operation of the Ti:Sa lasers [7] facilitated the high resolution spectroscopy of infrared transitions. These advancements of the RILIS laser setup combined with the LIST technique paved the way for the continuation of the polonium campaign at CERN towards neutron-rich isotopes, including 217;219Po, through a suppression of surface ionized francium of up to four orders-of-magnitude. In this contribution, we present the recent results of the in-source laser spectroscopy of polonium [8]. The results of the analysis of the isotope shift and hyperne spectra of 217Po, obtained by the first in-LIST laser spectroscopy combined with precise scanning of the narrow bandwidth Ti:Sa laser, show how 217Po delineates the region of odd-even staggering reversal for the charge radii. To demonstrate the diverse applications of in-source laser spectroscopy at RIB facilities, we will conclude by presenting the high precision determination of the ionization energy of the polonium atom obtained from the ovserved Rydberg spectrum [8]. [1] V.N. Fedosseev et al., Rev. Sci. Instrum. 83, 02A903 (2012) [2] T.E. Cocolios et al., Phys. Rev. Lett., 106:052503 (2011) [3] M.D. Seliverstov et al., Phys. Lett. B 719, 362-366 (2013) [4] D.A. Fink et al., Nucl. Instrum. Meth. B 317, 417421 (2013) [5] R.E. Rossel et al., Nucl. Instrum. Meth. B 317, 557560 (2013) [6] S. Rothe et al., Nat. Commun. 4, 1835 (2013) [7] S. Rothe et al., Nucl. Instrum. Meth. B 317, 561564 (2013)