Charge state distribution studies of SrF 3 , MnF 3 and CaF 3 molecules using single and double stripping in a Tandem accelerator Pankaj Kumar a,b,⇑ , G. Korschinek a , S. Chopra b , T. Faestermann a , P. Ludwig a , G. Rugel a , D. Seiler a , A. Wallner a,1 , S. Ojha b , S. Gargari b , R. Joshi b , D. Kanjilal b a Physik Department der Technische, Universität München, D-85748 Garching, Germany b Inter-University Accelerator Center (IUAC), PO Box 10502, New Delhi 110067, India article info Article history: Received 9 December 2010 Received in revised form 30 May 2011 Available online 2 June 2011 Keywords: Molecular beam Tandem accelerator Stripping foil Accelerator Mass Spectrometry abstract High energy beams of high ion currents from a Tandem accelerator are a common requirement in nuclear physics, materials science and Accelerator Mass Spectrometry (AMS) research. In many cases, molecular beams are chosen from the ion source to achieve a high ion source yield for the negative ions, or, as for AMS, to suppress isobaric interference. For this reason we have studied the use of consecutive stripper foils, double stripping, to increase the ion yield in conjunction with increased energy of injected molec- ular beams through a Tandem accelerator. By this method we could achieve a shift in the yield towards higher charge states. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Tandem accelerators are being used in various fields of research in science. Besides their classical applications in nuclear physics research, they are used as well in materials research like Elastic Recoil Detection (ERD) and ultrasensitive Accelerator Mass Spectrometry (AMS). But they are also used as a pre-injector, sup- plying ion beams for a post-accelerator, even for the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, USA [1,2]. For all of those a driving demand concerns the availability of high particle energies as well as high ion-yields. A key parameter for high energy of a Tandem accelerator at a given potential, is the charge state after stripping of the negative ions in the terminal. In Tandem accelerators the negative ions are produced in the ion source and then injected in the machine after mass analysis. The negatively charged ions are accelerated by the attraction of the positive potential at the terminal of the accelerator. Electrons are stripped off the negative ions as they pass through a thin foil or a gas at the high voltage terminal of the Tandem accelerator and that results in a distribution of positive charge states. This charge state distribution can be studied at the exit of the accelera- tor by a dipole magnet (Analyser) after the further acceleration of positive ions. Many studies have been carried out on the charge state distribution of atomic beams using a single stripper [2,3,20]. However often the ion source yields are too low or the negative ions are too short lived for acceleration; for example man- ganese [4] or nitrogen [5] do not form negative ions due to lack of the electron affinity. To overcome these problems, negative ions of molecules, which are readily formed, instead of negative ions of individual atoms, are injected into the Tandem accelerator. A fur- ther motivation for use of negative molecules is AMS research. One of the reasons for the high sensitivity of AMS is the suppres- sion of isobars by nuclear counting techniques; however, an appro- priate choice of negative molecules extracted from the ion source might already help in reducing the isobaric interference [6–9]. There are detailed studies on using the super-halogens in AMS to get higher ion source intensity, and to reduce the isobaric back- ground [10–13]. In these cases the study presented in this paper will add one more benefit in terms of higher beam current and higher energy through the accelerator. The stripping process for molecular beams is somewhat differ- ent than for atomic beams. There the ion of interest is accompanied during the passage through the stripper by all other ions of the ini- tial molecule. If they are close enough to the ion of interest, inter- ference during stripping can happen. Up to now there are only few studies about molecular beams and using a double stripper at the terminal area [14] concerning only energies in the low MeV range and low charge states. However, double stripping by the use of a gas followed by a foil is well known since long time [15,22]. The aim there is to improve 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.05.032 ⇑ Corresponding author at: Inter-University Accelerator Center (IUAC), New Delhi, India. Tel.: +91 11 2689 3955; fax: +91 11 2689 3666. E-mail addresses: baghelpankaj@gmail.com, pkb@iuac.res.in (P. Kumar). 1 Present address: Physics Division, Australian Nuclear Science and Technology Organization (ANSTO), PMB 1, Menai, NSW 2234, Australia. Nuclear Instruments and Methods in Physics Research B 269 (2011) 1986–1991 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb