The interactions of 300 MEV negative PI-Mesons with complex Nuclei

Abstract

A stack of emulsion pellicles has ben exposed to a 300 MeV beam of π(^-)-mesons and their interactions with nuclei have been observed by following 140 m of track. In order to analyse the events the usual techniques have been employed in addition to which a new method due to the author of measuring the ionization of tracks, steeply inclined to the emulsion plane, is presented. The interation lengths for the production of inelastic interactions and elastic scatterings are (37.9 ± 2.0)cm and (77.4 ± 5.8)cm respectively. An optical model analysis leads to an absorption coefficient and change in wave number of (1.5 ± 0.15) 10(^12) cm(^-1) and (1.32 ± 0.12) 10(^12) cm(^-1) respectively. The differences from the expected values are consistent with a reduction of the cross-section for elastic scattering within the nucleus of about 3 times. The average energy for inelastically scattered pions varies with the angle of scattering and resembles that for the scatting of pions by free, stationary nucleons except that the energy in the forward direction is somewhat reduced. The angular distribution for the scattered pions is somewhat reduced. The angular distribution for the scattered pions shows near isotropy whereas the equivalent graph for scatting on free nucleons is strongly peaked in for the forward direction. A mode of interaction in which only a single collision of the pion with a nucleon occurs is, proposed. The pion emerges without further collision and the struck nucleon goes on to make other collisions. The exclusion principle has been applied to an experimentally determined distribution of momentum in the nucleus and a strongly inhibitive effect results, producing an isotropic distribution of the secondary, pions and a lowering of the average energy of these pions in the forward direction. For absorption of the pion it is proposed that two absorbing nucleons are involved which go on to make other collisions. Energy balances have been performed on the inelastic scatterings and absorptive events. They show good agreement with the available energy.