V.N. Fedoseyev

Chemically selective laser ion-source for the CERN-ISOLDE on-line mass separator facility

Abstract Radioactive atoms produced in proton-induced nuclear reactions and released from thick targets have been ionized resonantly by laser radiation in a hot tube connected to the target container. Pulsed tuneable lasers with a repetition rate as high as 10 kHz have been applied for stepwise resonant excitation and photoionization in the last step. In this way the efficiency and selectivity of the target and ion source system which serves as an injector to the on-line isotope separators at CERN-ISOLDE could be improved. In a series of off-line and on-line studies the ionization of Sn ( E i = 7.3 eV), Tm ( E i = 6.2 eV), Yb ( E i = 6.2 eV) and Li ( E i = 5.4 eV) was investigated. An ionization efficiency of up to 15% was obtained for Yb. The ratio of the laser-ionized and surface-ionized ion currents was measured as a function of temperature for different ionization cavity materials (W, Ta, Nb and TaC). It was shown that this ratio, i.e. the selectivity, rises for Tm from 10 to 10000 with falling temperature and is strongly dependent on the material. Since the lasers are pulsed the ion beam becomes bunched with a pulse width of about 10–50 μs. This width is strongly dependent on the potential drop along the tube (caused by the electric current used for heating the tube) and on the alignment of the laser beams with respect to the tube axis. The selectivity could be further improved by a factor of 10 using gated detection of the bunched ion beam.

The ISOLDE laser ion source for exotic nuclei

At the ISOLDE on line mass separator a system of copper vapor lasers and dye lasers serves for resonant ionization of atoms inside a hot cavity attached to the target. Radioactive ion beams of Yb, Ag, Mn, Ni, Zn, Be, Cu, Cd and Sn were produced with the Resonance Ionization Laser Ion Source (RILIS). Two and three step excitation schemes are used, providing an ionization efficiency of about 10%. Thanks to the use of the RILIS it became possible to ionize beryllium efficiently at ISOLDE, and all particle stable Be isotopes could be separated for the first time. Separation of Ag and Cu nuclear isomers was achieved in the ion source by appropriate tuning of the laser wavelength. New isotopes of Ag, Mn, Zn, Cd and Sn were found, including the r process “waiting point” nucleus 129Ag.

CHEMICALLY SELECTIVE LASER ION SOURCE OF MANGANESE

Abstract Ion beams produced by on-line isotope separators are often contaminated by abundantly produced isobars. This significantly complicates, and in a number of cases renders impossible, the realization of physical experiments with such beams. In many cases the purity of the ion beams may be improved on the ionization stage of the isotope separation using a laser resonance ion source. The method of laser resonance ionization of atoms in a hot cavity has been applied for chemically selective production of Mn ion beams at the CERN-ISOLDE facility. Radiation of pulsed dye lasers and copper vapor lasers provided three-step excitation and ionization of Mn isotopes in the ordinary W surface ionizer, connected to the target container. High values of efficiency and selectivity obtained with the laser ion source made it possible to suppress substantially an admixture of 57 Fe in the 57 Mn ion beam and to perform Mossbauer experiments on implanted impurities in solids.

Production of radioactive Ag ion beams with a chemically selective laser ion source

Abstract We have developed a chemically selective laser ion source at the CERN-ISOLDE facility in order to study neutron-rich Ag nuclides. A pulsed laser system with high repetition rate has been used based on high-power coppe-vapour pump lasers and dye lasers. With this source significant reductions of the isobaric background has been achieved.

Selective laser ionization of radioactive Ni-isotopes

Abstract A chemically selective laser ion source based on resonance ionization of atoms in a hot cavity has been applied in the study of Ni-isotopes at the CERN-ISOLDE on-line isotope separator. Laser ionization enhanced the yields of long-lived Ni-isotopes almost four orders of magnitude when compared to the yields obtained with the surface ionization mode of the source. As a result, high yields of long-lived Ni-isotopes were obtained. Separation efficiencies of 0.3 and 0.8% were obtained for Ni produced in uranium-carbide, produced from uranium-di-pthalocyanine, and Ta-foil targets, respectively. Ni was found to be released very slowly from the present target and ion source combination.

Production of photoionic gallium beams through stepwise ionization of atoms by laser radiation

Production of intensive (up to 1 mA) ionic beams through stepwise photoionization of atoms induced by laser radiation is investigated. Optimum photoionization schemes are presented. A photoionic gallium beam is obtained with an average current value of 2.5 μA.

Isomer separation and measurement of nuclear moments with the ISOLDE RILIS

Short-lived radioisotopes are element selectively ionized by the resonance ionization laser ion source (RILIS) of the on-line isotope separator ISOLDE (CERN). The relative production of low and high spin isomers can be significantly changed when a narrow-bandwidth laser is used to scan through the atomic hyperfine structure. This allows the assignment of gamma ray transitions to the decay of the individual isomers. Moreover, the measurement of the hyperfine splitting provides a very sensitive method for the determination of magnetic moments of exotic isotopes. The technical developments are discussed for the example of copper.

Laser ionization in β decay studies of Zn and Mn nuclei

Resonance ionization laser ion source (RILIS) technique has been used in the β-decay studies of 59Mn and 58Zn. The importance of the RILIS for production of these elements is discussed. The properties of the low-lying levels of the studied nuclei are discussed.

A chemically selective laser ion source for on‐line mass separation

Laser resonance ionization has been applied to ionize radioactive atoms released from thick ISOLDE/CERN targets. Laser light from pulsed dye lasers with a high repetition rate (10 kHz) was used for stepwise excitation and ionization. By this method, efficiency as well as the selectivity of the target/ion source system could be improved. In a series of off‐line and on‐line studies, the resonance ionization of elements with different ionization potentials, such as Yb (Ei=6.2 eV), Tm (Ei=5.8 eV) and Sn (Ei=7.3 eV), was investigated. For Yb, photoionization efficiencies of up to 15% have been measured. An efficiency of 0.2% was obtained for Sn at the on‐line separator ISOLDE‐3. However, this value can be improved by about two orders of magnitude using a transition to an autoionizing state at 59 375.9 cm−1.

Beta decay of the new isotope 101Sn

The very neutron-deficient isotope 101Sn was produced in a 50Cr(58Ni, 2p5n) reaction and its decay properties were determined for the first time. By using chemically selective ion sources of an on-line mass separator, the energy spectrum and the half-life (3 ± 1 s) of beta-delayed protons of 101Sn were measured. These results are compared to theoretical predictions.