1. F. Calligaris, C. Cernigoi, I. Gabrielli and F. Pellegrini, Nucl. Phys. A 126, 209 (1969).
2. G. Charpak, J. Fawier, L. Massonet and C. Zupancic, Int. Conf. on Nuclear Physics, Gutlinburg — Tennessee, Sept. (1966);
3. C. Zupancic, Proc. Sec. Int. Conf. on High Energy Physics and Nuclear Structure, Rehovoth (1967);
4. T. Bressani, G. Charpak, J. Fawier, L. Massonet, W.E. Meyerhof and C. Zupancic, Phys. Lett. 25B, 409 (1967).
5. M.E. Nordberg, K.F. Kinsey and R.L. Burman, University of Rochester, UR-875–210.