Review of resonant laser ionization sources for on-line mass separators for radioactive ion beams (invited) (abstract)

Abstract

The basic operation principles of laser ion sources (LIS) based on resonance ionization of atoms in a hot cavity are discussed. Since the atom of each element has its own specific energy level structure the ionization process has an exceptionally high elemental selectivity if the laser radiation frequencies coincide with the atomic transition frequencies. The efficiency of a single laser pulse ionization may reach tens of percent. If a sample containing studied isotopes is placed in a closed hot cavity and light beams of high repetition rate lasers are introduced into the cavity via a small hole which is also used for extraction of the photoions, the overall efficiency of such an ion source may also reach tens of percent. The elemental selectivity of the LIS will be determined by the efficiency of the surface ionization of undesirable isotopes and the efficiency of laser ionization of the studied isotope. The LIS is naturally coupled with the mass separator because the diameter of the cavity hole is small (1–3 mm). Rydberg levels of Fr were studied using LIS in off-line experiments at the Institute of Spectroscopy/Troitzk. The production rate of a Fr isotope source was around 1000 atom/s. The LIS has been applied to produce radioactive ion beams at IRIS/St.-Petersburg, ISOLDE/CERN, and GSI/Darmstadt on-line facilities. At GSI neutron-deficient Sn (102,103,104) isotopes have been studied using the LIS. The on-line measured overall efficiency of the LIS was equal to 8.5%. At ISOLDE neutron-rich Ag (121–127) isotopes produced by the LIS have been studied by a neutron long counter and beta detector. The efficiency of the LIS measured in off-line experiments with stable isotopes is as great as 11%. The LIS of Yb, Sm, Sn, Li, and Ni have also been developed at ISOLDE. At the IRIS the LIS was used to obtain radioactive beams of Yb and Ho.