A brief account is given of some high energy disintegrations initiated in photographic emulsions by primary cosmic-ray particles at about 90,000 feet above sea level. In particular, six events which show only relativistic or near relativistic fragments and a typical forward cone of shower particles are described in detail. The angular distribution of the shower particles is, in some of these cases, consistent with them, being due to the multiple production of mesons in a single interaction between an incoming nucleon and a hydrogen nucleus, or a nucleon on the edge of a heavier nucleus, according to the mechanism of Fermi's recent theory. One of these events has thus been interpreted as a collision between an incoming lithium nucleus with an energy of about 2×${10}^{12}$ ev per nucleon and a hydrogen nucleus in the emulsion.

• Received 4 September 1951

DOI:https://doi.org/10.1103/PhysRev.84.1190