Nuclear Instruments and Methods in Physics Research A 481 (2002) 1–8 The charge state distribution of a carbon beam measured at the lund pelletron accelerator with the newly installed terminal pumping system in use Madis Kiisk a, *, Bengt Erlandsson a , Mikko Faarinen a , Ragnar Hellborg a , Kjell H ( akansson a , Per Persson a ,G . oran Skog b , Kristina Stenstr . om a a Department of Physics, Lund University, S . olvegatan 14, SE-22362 Lund, Sweden b Radiocarbon Dating Laboratory, Department of Quaternary Geology, Lund University, Lund, Sweden Received 7 May 2001 Abstract Charge state distributions for 12 C and 13 C ions have been measured at the Lund Pelletron tandem accelerator for the N 2 gas stripper with a newly installed terminal pumping system in use. A comparison of the results obtained for the ion energies between 1.5 and 2.8MeV with the foil stripper and the gas stripper without terminal pumping demonstrates the great improvement of the stripping process achieved with the new terminal pumping. r 2002 Elsevier Science B.V. All rights reserved. 1. Introduction In most types of experiments using a tandem electrostatic accelerator, it is valuable to know the distribution in the beam of the charge states obtained in the stripping system at the accelerator high voltage terminal. With the knowledge of the distribution it is possible to optimise the selection of the terminal voltage and the suitable ion charge state for each experiment. In most tandem accelerators both foil and gas strippers are available. The advantage of a gas stripper compared to a foil stripper is the better stability of the transmission over time. Due to radiation damage, the transmission through a foil will constantly alter. The disadvantages of gas stripping are a lower beam transmission and a lower mean charge state at a given terminal voltage. As the negative ions enter the stripper medium, a certain distribution of the positive charge states will result. This distribution will change with depth until, at a certain depth, equilibrium between the different charge states is reached. This equilibrium distribution [1] is to a first approximation a function of the nuclear charge and the velocity of the ions [2]. When the positive ions are accelerated from the terminal potential to ground potential, ions of different charges acquire different energies. With a simple particle detector placed in the beam pipe after the accelerator, and by detecting the elastically backscattered ions in a suitable target, it *Corresponding author. Tel.: +46-46-222-7607; fax: +46- 46-222-4709. E-mail address: madis.kiisk@nuclear.lu.se (M. Kiisk). 0168-9002/02/$-see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0168-9002(01)01255-4