A new laser technique developed by a collaboration involving GANIL has allowed for the first study of the structure of different isotopes of actinium. Resonant ionization spectroscopy in a gas will allow for the study of very heavy radioactive nuclei produced in small quantities by SPIRAL2 (one nucleus every ten seconds).
Using several lasers appropriately tuned in energy makes it possible to selectively extract one or more electrons from atoms (i.e. to photo-ionize them). Nuclear physicists use this method to prepare ultra-pure ion beams. They can now use it to probe the structure of very exotic nuclei, even when they are only present in very low quantities.
By accelerating stable neon nuclei (Z = 10) on a thin gold target (Z = 79), the scientists produced actinium nuclei (Z = 89) which they then "stopped" in a volume of gas to convert them into neutral atoms. Lasers were then used to selectively ionize these atoms and resonance "peaks" that provide structural information on the nuclei were obtained by tuning the energy of the lasers.
By ionizing the atoms in a supersonic jet rather than at rest in a gaseous cell, the scientists were able to gain a factor of ten in resolution—a valuable asset in studying the detailed structure of the peaks.
These experiments were carried out under supervision of the Institute for Nuclear and Radiation Physics of Louvain-la-Neuve University in Belgium, in collaboration with CNRS and GANIL, with instruments developed at GANIL for the Super Separator Spectrometer (S3).
* R. Ferrer et al. “Towards high-resolution laser ionization spectroscopy of the heaviest elements in supersonic gas jet expansion.” Nat. Commun. 8, 14520 doi:10.1038/ncomms14520 (2017).