Gas purification studies at IGISOL-4
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Gas purification studies at IGISOL-4 I. Pohjalainen · I. D. Moore · T. Eronen · A. Jokinen · H. Penttil¨a · S. Rinta-Antila
© Springer Science+Business Media Dordrecht 2014
Abstract A new gas purification system has been constructed at the upgraded IGISOL facility, Jyv¨askyl¨a, to meet the need for ultra-high purity helium and argon buffer gas used in the ion guide technique. The purification of helium using liquid nitrogen-cooled cold traps is investigated and compared with unpurified gas using mass spectra obtained at the focal plane of the separator. Neon, an impurity intrinsic to the in-house recycled helium, was seen to have high sensitivity to the impurity level of the gas which is expected to reach sub-parts-per-billion level. Keywords Gas cell · Buffer gas · Gas purification · Gas impurities
1 Introduction Perhaps the most critical factor affecting the efficient use of noble gas-filled ion guides and gas catchers for the production of low-energy radioactive ion beams is the purity of the gas. At the Ion Guide Isotope Separator On-Line (IGISOL) facility at the Accelerator Laboratory of the University of Jyv¨askyl¨a (JYFL) the ion guide method has been successfully used for over three decades [1]. In brief, a primary beam from a cyclotron impinges on a thin target inside a gas cell filled usually with helium but occasionally argon. The nuclear reaction products recoil out of the target, stop and thermalize in the buffer gas while their charge Proceedings of the 9th International Workshop on Application of Lasers and Storage Devices in Atomic Nuclei Research “Recent Achievements and Future Prospects” (LASER 2013) held in Poznan, Poland, 13–16 May, 2013 I. Pohjalainen () · I. D. Moore · A. Jokinen · H. Penttil¨a · S. Rinta-Antila Department of Physics, University of Jyv¨askyl¨a, Survontie 9, PL 35 (YFL), 40014 Jyv¨askyl¨a, Finland e-mail: [email protected] I. D. Moore e-mail: [email protected] T. Eronen Max-Plank-Institut f¨ur Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
I. Pohjalainen et al.
state decreases. The ions, primarily singly-charged, are swept out through an exit hole in the ion guide by the gas flow and are guided towards a mass separator via a radiofrequency sextupole ion guide [2]. Trace impurities in the buffer gas play a crucial role in the ion survival during evacuation from the gas cell and understanding the impurity-related processes is necessary for ion guide development. Although the evacuation time of ions is often too fast for molecular formation, the presence of impurities affects the final charge state of the ions during thermalization. The importance of gas phase chemistry comes into play with larger gas cells and with slower evacuation times. In particular, the development of the laser ion source at IGISOL has shown the importance of the gas purity, especially for chemically active elements [3, 4]. Impurities at the level of parts-per-million (ppm) have a significant effect on the ion guide operation by reducing the efficiency of extracting atomic ions of i
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