Nobel prize to C. F. Powell awarded in 1950 "for his development of the photographic method of studying nuclear processes and his discoveries regarding mesons made with his method''
Brown, R.H.; Camerini, U.; Fowler, P.H.; Muirhead, H.; Powell, C.F.; Ritson, D.M.; Observations with Electron Sensitive Plates Exposed to Cosmic Radiation. II. Further Evidence for the Existence of Unstable Charged Particles of Mass ~ 1000 me and Observations on their Mode of Decay
Nature 163 (1949) 82;
R. N. Cahn and G. Goldhaber, The Experimental Foundations of Particle Physics, Cambridge Univ. Press (1991) 72.
An event is described which offers further evidence for the existence of mesons of mass > -particles. A particle, of which the mass, as determined by grain counts, is ~ 1000 me, comes to rest in the photographic emulsion and leads to the emission of three charged particles, one of which is apparently a -meson. Evidence is given which suggests that the event corresponds to the spontaneous disintegration of the heavy
particle into 3 charged mesons, whose masses are in the 200 - 300 me, region. (Science Abstract, 1949, 1974, U. C.).
Related references More (earlier) information appears in R. H. Brown et al., Nature 163 (1949) 47;
See also L. Livingston and H. A. Bethe, Rev. of Mod. Phys. 9 (1937) 263;
Analyse data from Alichanian, Alichanov, and J. Weissenberg, Zh. Eksp. Teor. Fiz. 18 (1948) 301;
U. Camerini, H. Muirhead, C. F. Powell, and D. M. Ritson, Nature 162 (1948) 433;
C. M. G. Lattes, G. P. S. Occhialini, and C. F. Powell, Proc. Roy. Soc. 61 (1948) 173;
C. Dilworth, G. P. S. Occhialini, and Payne, Nature 162 (1948) 102;
G. P. S. Occhialini and C. F. Powell, Nature 162 (1948) 168;
O. Halpern and H. Hall, Phys. Rev. 73 (1948) 477;
G. D. Rochester and C. C. Butler, Nature 160 (1947) 855;
L. Leprince-Ringuet, Compt. Ren. 226 (1948) 1897;
Goldschmidt-Clermont, C. F. Powell, and D. M. Ritson, Proc. Roy. Soc. 61 (1948) 138;
K+ 2charged+ charged
First evidence for three-prong kaon decay.