Article révisé par les pairs
Résumé : Ilford G.5 plates were exposed to slow π--mesons produced by the Rochester Cyclotron. About 1500 σ-stars were classified according to the number of prongs and according that they were produced in a light nucleus (C, N, O) or a heavy nucleus (Br, Ag) of the emulsion. The examination of stars produced in the light nuclei has allowed to investigate the modes of desintegration of these nuclei. An extension of the scheme of Clark and Ruddlesden is proposed which gives an account of about 2/3 of the observed stars. The remaining stars contain at least one fragment (Z > 2) and seem better interpreted by a mechanism of local heating. © 1956 Società Italiana di Fisica.