Nuclear Interactions in Gold of Secondary Particles Emitted in Penetrating Showers

Abstract

A large counter controlled cloud chamber containing 16 gold plates totaling 308 g/${\mathrm{cm}}^{2}$ in thickness was operated at an altitude of 11,500 ft. Forty of the pictures of penetrating showers obtained were selected for the determination of the mean free path for nuclear collisions of ionizing secondary particles. The result was found to be 230\ifmmode\pm\else\textpm\fi{}60 g/${\mathrm{cm}}^{2}$, corresponding to 0.7\ifmmode\pm\else\textpm\fi{}0.2 times the cross section equal to the geometric area of the gold nucleus. The 14 percent of the nuclear events used in making this determination were large angle scatterings of a penetrating secondary particle with no observable disintegration products emerging from the gold plate in which the scattering occurred. The number of secondary nuclear events occurring, which are not observed because of the absorption of all tertiary particles, was estimated to be 18 percent of the total. The momenta of the secondary particles used in this determination ranged between ${10}^{9}$ and ${10}^{10}$ ev/c. The lowest energy penetrating shower which has a high probability of tripping the counter coincidence circuit used was estimated to be 1.5\ifmmode\times\else\texttimes\fi{}/${10}^{10}$ ev.The number of high energy protons among the secondary particles used in the determination of the collision mean free path was less than 11 percent, and the total fraction of protons is less than 30 percent. The 88\ifmmode\pm\else\textpm\fi{}3 percent of the penetrating showers observed in the experiment showed the presence of an observable electron cascade. The average number of penetrating secondaries of minimum ionization emitted in penetrating showers of an average energy of 3\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ev, and either not showing any electronic cascade or showing the presence of an electronic cascade having an energy less than or equal to 7\ifmmode\times\else\texttimes\fi{}${10}^{9}$ ev, is 7\ifmmode\pm\else\textpm\fi{}1 per shower. The corresponding average multiplicity of secondary particles of minimum ionization in penetrating showers of 6\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ev average energy, which show the presence of an electron cascade of an energy greater than 7\ifmmode\times\else\texttimes\fi{}${10}^{9}$ ev, is 11\ifmmode\pm\else\textpm\fi{}2 per shower. Evidence is given that the angular distribution of the mesons in the center-of-mass system of a nucleon-nucleon collision at energies above 1.5\ifmmode\times\else\texttimes\fi{}${10}^{10}$ ev is not isotropic and is probably collimated in two cones of about 50\ifmmode^\circ\else\textdegree\fi{} half-angle around the directions of the velocities of the nucleons in the center-of-mass system.