Nuclear Interactions and Mean Free Paths of Protons, Neutrons, and Alpha Particles at Energies Around 250 Bev/Nucleon

Abstract

Nuclear interactions of protons, neutrons, $\ensuremath{\alpha}$ particles, and heavier nuclei of average energy 250 Bev/nuc were studied in nuclear emulsion. The source of these particles were fragmentations of heavy primary nuclei of the cosmic radiation. Their energy was determined from multiple scattering measurements. The interaction mean free path for protons is 41\ifmmode\pm\else\textpm\fi{}10 cm, for $\ensuremath{\alpha}$ particles 27\ifmmode\pm\else\textpm\fi{}7 cm. The mean free path shows no significant change compared with measurements at lower energies. The mean number of shower particles $〈{n}_{s}〉$ depends appreciably on the mass of the target nucleus. Our best estimate for nucleon-nucleon collisions at 250 Bev is $〈{n}_{s}〉=8.8\ifmmode\pm\else\textpm\fi{}1.9$. A detailed comparison of the estimate of the primary energy obtained from the angular distribution of shower particles with the true primary energy is carried out. The angular distribution of the shower particles will, in an individual case, give a quite unreliable value for the primary energy. In the average, the angular distribution method will over-estimate the true primary energy by a factor of 1.3 for interactions with a number of heavy prongs ${N}_{h}\ensuremath{\le}5$. If ${N}_{h}g5$, the angular distribution will underestimate the true energy in the average by a factor of 1.8. The angular distributions can be transformed into a system in which they are symmetric. This is even true for collisions with heavy target nuclei (${N}_{h}g5$). The results for alpha particle and heavy nucleus collisions are quite similar.The inelasticity for the proton and neutron interactions shows large fluctuations for individual events. It depends weakly on the number of shower particles and on the mass of the target nucleus. Its mean value is 50%. The mean value for the alpha-particle collisions is 22%.