Figure 1: In-gas-jet laser ionization and spectroscopy setup.

Short-lived actinium isotopes are produced in the fusion reaction of accelerated neon ions on a gold target. After thermalization and neutralization in purified argon, the actinium atoms are evacuated out of the gas cell through a de Laval nozzle. Just before the nozzle, an electric field is created to collect the remaining ions by applying a DC voltage on a pair of electrodes indicated by a + and a − sign. The resulting collimated supersonic gas jet at Mach ∼6 provides a quasi-collisional free environment at a low temperature (T∼30 K). The gas jet, containing the reaction products, is overlapped with the laser beams to resonantly ionize actinium. The ions are subsequently sent out from the gas cell chamber towards the mass separator through a radiofrequency (RF) ion guide and their decay radiation is finally recorded. The pressure conditions (colour code on a logarithmic scale) range from 350 mbar in the gas cell to the 0.03 mbar background pressure in the gas cell chamber. The setup is not shown to scale.