Département de Physique Nucléaire

Laser spectroscopy studies provide charge radii, spins and nuclear moments, key ingredients to test and validate nuclear models. To perform laser spectroscopy on exotic nuclides, the highest efficiencies in combination with a high spectral resolution are required. The In-Gas Laser Ionization and Spectroscopy (IGLIS) technique whereby radioactive atoms stopped in a buffer gas cell and subsequently positioned in a supersonic gas jet produced by a de Laval nozzle are resonantly ionized using resonant, multistep laser ionization, fulfills these requirements.

In the last years IGLIS was employed within the gas cell at the LISOL facility (Leuven Isotope Separator On-Line) to measure magnetic moments of 57-59Cu [1] and 97-101Ag [2]. A typical spectral resolution of 5 to 10 GHz was obtained. The measurements were recently extended to the heavy mass region by resolving the hyperfine structure of neutron deficient actinium isotopes 212-215Ac. Carrying out laser ionization in the low-temperature and low-density supersonic gas jet formed using a ‘de Laval’ nozzle allows eliminating the pressure and Doppler broadening thus improving significantly the spectral resolution [3].

The in-gas jet laser ionization spectroscopy was recently proven in an on-line experiment measuring the short-lived 214,215Ac isotopes produced in the 22Ne(197Au,xn) reaction. A narrow bandwidth, high repetition rate laser system has been used to investigate the hyperfine structure of the 438 nm atomic transition in actinium. The data obtained reveal a total spectral resolution of ~400 MHz. The isotope shifts as well as the hyperfine A- and B- parameters, and thus magnetic dipole and electric quadrupole moments, could be extracted and a firm spin assignment for the N=126 215Ac (T1/2=0.17 s) and 214Ac was obtained. The results are compared to nuclear shell-model calculations.

By exploring the physical and technical limits of this new approach for laser spectroscopy studies at the newly commissioned laser laboratory at KU Leuven, the best performance in spectral resolution and ionization efficiency for the IGLIS-based setup [4] linked to the Superconducting Separator Spectrometer (S3 - GANIL) can be obtained. The reach of this new approach to study the atomic and nuclear physics properties of the heaviest elements will be discussed.

[1] Cocolios,- PRL 103 (2009) 102501; [2] Ferrer,- PLB 728 (2014) 191; [3] Kudryavtsev,- NIM 297 (2013) 7; [4] Ferrer,- NIMB 317 (2013) 570.