Thursday, March 10, 2016, 16:00
WHGA Auditorium
Thomas Elias Cocolios, KU Leuven
Abstract: Since the discovery of the large isomer shift in 185Hg 35 years ago [1], the study of changes in the nuclear charge radii in the region of Z=78-88 (platinum to radium) has been prolific [2]. The study of isotope shifts in atomic transitions has allowed the systematic study of the changes in the nuclear mean-square charge radii, although the extraction of the nuclear parameter from the atomic observable relies on an empirical description which has its limitations [3]. Interesting phenomena have nonetheless been addressed, like the onset of collective behaviour in the polonium isotopes [4], or the investigation of the region of reflexion asymmetry [5]. The typical approach is to compare the trend of long isotopic chains with respect to that of lead, which represents the magic shell closure, the spherical reference in the region [6].
This picture, however, is highly biased on the isotope that one may choose as the reference, as well as the freedom that is left by the systematic uncertainty on the atomic parameters. Furthermore, the offset placed between the different isotopic chains is often arbitrary for better display. A look at the charge radii on absolute scale is seldom considered. In particular, the lack of absolute charge radii beyond bismuth (Z=83) prevents the heaviest isotopes in the region of interest to be addressed. In this colloquium, I shall explore the absolute charge radii in the Z=82 region, and discuss whether additional observations can be made. Ideas for the measurement of absolute charge radii beyond Z=83 will also be presented.
[1] G. Ulm et al, Isotope shift of 182Hg and an update of nuclear moments and charge radii in the isotope range 181Hg-206Hg , Z. Phys. A 325 (1986) 247-259.
[2] P. Campbell, I.D. Moore & M.R. Pearson, Laser spectroscopy for nuclear physics, Progress in Part. and Nucl. Phys. 86 (2016) 127-180.
[3] B. Cheal, T.E. Cocolios & S. Fritzsche, Laser spectroscopy of radioactive isotopes: role and limitations of accurate isotope-shift calculations, Phys. Rev. A 86 (2012) 042501.
[4] T.E. Cocolios et al, Early onset of ground state deformation in neutron deficient polonium isotopes, Phys. Rev. Lett. 106 (2011) 052503.
[5] I. Budincevic et al, Laser spectroscopy of francium isotopes at the borders of the region of reflection asymmetry, Phys. Rev. C 90 (2014) 014317.
[6] H. De Witte et al, Nuclear charge radii of neutron-deficient lead
isotopes beyond N=104 mid shell investigated by in-source laser
spectroscopy, Phys. Rev. Lett. 98 (2007) 112502.