1. G.P. Westphal,Nucl. Instrum. Methods, 136 (1976) 271.
2. F. Grass, G.P. Westphal, T. Kasa,Nucl. Geophys., 1–3 (1987) 253.
3. A. Salahi, F. Grass, T. Kasa, E. Seidel, S. Roth,J. Trace Microprobe Techn., 6 (1988) 229.
4. D.A. Becker, R.M. Lindstrom, J.K. Langland, R.R. Greenberg,J. Trace Microprobe Techn., 14 (1996) 1.
5. G.P. Westphal,J. Trace Microprobe Techn., 14 (1996) 57.