Speaker
Description
The lanthanide elements, being located around the Z = 64 “sub-magic” proton subshell closure and all crossing the N = 82 neutron shell gap, offer a unique testing ground for nuclear theory. Benchmark cases range from strongly pronounced odd-even-staggering of charge radii vanishing in isomers (around Sm-141) [1], abrupt transitions from spherical to strongly deformed nuclei (for N < 75) [2], to possible octupole deformation (around Eu-154) [3]. Additionally, pushing towards the proton drip line will elucidate the phenomenon of proton emission amongst others in the thulium and lutetium isotopic chains [4,5].
Extensive studies in this region at ISOL facilities are heavily jeopardized by strong prevalent ion beam contamination. This is due to significant surface ionization rate of the lanthanides themselves and the neighboring cesium and barium isobars, often even presenting radiation protection issues in the experimental hall. Fast beam collinear high resolution laser spectroscopy additionally suffers from thinning of level population if charge exchange to atomic form is employed, due to the large quantity of atomic states in the complex electronic structure with open f shells. The latter also effectuates rich and dense hyperfine structure spectra caused by high angular momenta of the involved states, necessitating sufficient experimental resolution.
ISOLDE’s novel specialized laser ion source PI-LIST (Perpendicularly illuminated Laser Ion Source and Trap) [6] tackles these obstacles by utilizing surface ionization contamination suppression in the ion source in combination with strongly reduced Doppler broadening in a crossed laser / atom beam interaction geometry. Its first-time experimental utilization in 2022 on actinium proved achievable resolution in the order of 100 MHz, while extensive off-line work on lanthanide laser ionization schemes in the community [7,8] paves the way to its broad application in this region.
This year, a campaign to measure extractable yields of lanthanides from a tantalum foil target with a PI-LIST was launched [9]. Follow-up experimental proposals entail, e.g., nuclear structure investigations on the praseodymium isotope chain which to date exhibits the scarcest experimental data in this part of the nuclear chart [10]. Additionally, a tailored resonance ionization laser scheme is being developed for this purpose.
References
[1] V S Letokhov et al 1992, J. Phys. G 18 1177
[2] G A Leander et al 1982, Phys. Lett. B 110.1, 17-20
[3] G D Alkhazov et al 1990, Z. Physik A 337, 257–259
[4] O Klepper et al 1982, Z. Physik A 305.2, 125-130
[5] S Hofmann et al 1982, Z. Physik A 305.2, 111-123
[6] R Heinke et al 2023, NIM B 541, 8-12
[7] R Heinke et al 2021, Front. Med. 8
[8] D Studer et al 2020, Eur. Phys. J. A 56, 69
[9] K Chrysalidis et al 2022, CERN-INTC-2022-042, INTC-I-246
[10] N Frömmgen et al 2019, Hyperfine Interact 240, 66
