1. For a review of such experiments, see e.g. C.S. Wu, in:Alpha-, Beta-, Gamma-Ray Spectroscopy, ed. K. Siegbahn (North-Holland, Amsterdam, 1968).
2. R. Daudel, P. Benoist, R. Jacques and M. Jean, Comptes. Rend. 224(1947)1427;
3. R. Daudel, M. Jean and M. Lecoin, Comptes. Rend. 225(1947)290;
4. R. Daudel, M. Jean and M. Lecoin, J. de Phys. 8(1947)238.
5. R.M. Sherk, Phys. Rev. 75(1949)789.