V. I. Mishin

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.

Resonant laser ionization of radioactive atoms

Abstract Intense radioactive ion beams are produced by the isotope separation on-line method. The resonance ionization laser ion source (RILIS) can provide the chemical selectivity to separate beams with reduced isobaric contamination. The hot cavity RILIS at ISOLDE (CERN) uses copper vapor laser pumped dye lasers for the resonant transitions. Up to now 22 elements have been ionized with efficiencies of the order of 10%. Additional elements have been ionized with similar RILIS set-ups at the Institute of Spectroscopy (Troitsk), IRIS (Gatchina), Mainz University and TIARA (Takasaki). Ideas are discussed for future developments of this type of RILIS, which could further improve the efficiency, selectivity, rapidity of release and stability of the operation. The RILIS can also be applied for atomic spectroscopy studies of exotic radioactive isotopes, which are produced at rates of few atoms per second only. An interesting parallel is shown to the atomic vapor laser isotope separation (AVLIS), a large-scale application of resonance ionization, which could be used for the isotope enrichment of macroscopic amounts: tens of kg per h.

Resonance laser ionization of atoms for nuclear physics

The applications of the laser resonance ionization method in nuclear research are reviewed. Investigation of radioactive isotopes using resonance ionization techniques provides a valuable combination of high selectivity, efficiency and spectral resolution. The majority of radioactive ion beams produced at on-line isotope separator facilities profit from the selectivity and universal applicability of laser ion sources. Numerous ultra-sensitive and high-resolution techniques of laser spectroscopy based on resonance ionization of atoms have been developed for the study of rare and radioactive isotopes. A summary of ionization schemes applied to radioactive isotopes is given in table form.

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.

A new measurement of the 7Be(p,γ)8B cross-section with an implanted 7Be target

Abstract The 7 Be(p, γ ) 8 B capture reaction is of major importance to the physics of the sun and the issues of the “solar neutrino puzzle”. We report here on a new determination of the absolute cross section of this reaction, using a novel method which overcomes some of the major experimental uncertainties of previous measurements. We utilize a 7 Be target implanted into a Cu substrate and a uniformly scanned particle beam larger than the target spot, eliminating issues of target homogeneity and backscattering loss of 8 B reaction products. The target was produced using a beam of 1.8·10 10 /s 7 Be nuclei extracted at ISOLDE (CERN) from a graphite target bombarded by 1 GeV protons in a two-step resonant laser ionization source. The 7 Be nuclei were directly implanted into a copper substrate to obtain a target of 2 mm diameter with a total of 3.10 15 atoms. The measurement of the 8 B production cross section was carried out at the Van de Graaff laboratory of the Weizmann Institute of Science. We obtain for the S factor of the reaction: S 17 ( E cm = 1.09 MeV) = 22.7(1.2) eV. barn and S 17 ( E cm = 1.29 MeV) = 23.8(1.5) eV. barn, somewhat higher than other recent measurements. The present results can serve as a benchmark for further measurements of this cross section.

Resonance ionization spectroscopy on a fast atomic ytterbium beam

High-resolution laser spectroscopy for the study of nuclear sizes and shapes J Billowes and P Campbell High resolution laser spectroscopy of atomic systems R C Thompson High-resolution laser spectroscopy of Fr ns and nd Rydberg levels E Arnold, W Borchers, M Carre et al. Resonance laser ionization of atoms for nuclear physics V N Fedosseev, Yu Kudryavtsev and V I Mishin Laser detection of single atoms Viktor I Balykin, G I Bekov, V S Letokhov et al. Precision atomic physics techniques for nuclear physics with radioactive beams Klaus Blaum, Jens Dilling and Wilfried Nortershauser Resonance ionization spectroscopy on a fast atomic ytterbium beam

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.

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.