Laser spectroscopy of radioisotopes and isomers at the igisol facility, Jyväskylä

Abstract

We report on the progress of the collinear laser spectroscopy programme at the IGISOL isotope separator in Jyv~kyl~i. The sensitivity of the photon-ion coincidence tecnique has been sufficient to measure isotope shifts and hyperfine structures of light hafnium isotopes produced in 175Lu(p,xn) reactions. A gas-filled RF quadrupole has recently been installed in the beamline to reduce the energy spread and emittance of the ion beam. It is expected to increase the sensitivity of the laser technique by at least an order of magnitude, allowing measurements on a number of high-spin isomers in the hafnium chain. Status of the laser programme at the IGISOLOur laser collaboration decided to base its research programme at the IGISOL facility in Jyv/iskyl~ for two reasons. Firstly, the radioactive beam fluxes suited our ion-photon coincidence technique [1], which had been developed at the Daresbury Laboratory Nuclear Structure Facility. Secondly, it would allow refractory elements and millisecond isomers to be studied on-line for the first time.Considerable development work and effort were needed to adapt the IGISOL ion beam properties to the requirements of the laser technique, and it was three years before a resonance of a refractory radioisotope was observed. This was on the 327.6nm transition in the 8SZr+ ion produced in the sgy(p,2n) reaction with a 25 MeV proton beam of 15 #A. The ion beam flux was 12,000 ions/sec, of which approximately 8,000 ions/sec were SSZr. During the development time, four problem areas were identified: (i) the energy spread of the IGISOL ion beam increased rapidly with the voltage on the skimmer plate [2] and a compromise in ion source efficiency was necessary to limit it; (ii) background beams of isobaric contaminants (molecular ions) could give unacceptably high counting rates in the ion detector, increasing the random rate in the coincidence system. These beams could be significantly reduced by baking and conditioning the IGISOL chamber before use, and running with more effective cooling; (iii) off-line laser fluorescence tests showed that many ionic metastable states were populated in the ion source (in this case, from