The Properties of Particles Producing High Energy Nuclear Collisions in Gold

A large multiplate counter controlled cloud chamber containing 300 g/${\mathrm{cm}}^2$ of gold has been used for the study of penetrating showers at an altitude of 11,500 ft. The minimum energy required to trip the counter control efficiently was about 15 Bev. Counters located inside the chamber made it possible to observe events initiated by both ionizing and non-ionizing particles. It was found that at least 83.5 percent of the particles initiating these high energy events were ionizing. From the distribution of events in the plates of the chamber, the mean free path in gold for the particles producing these penetrating showers was found to be 145±15 g/${\mathrm{cm}}^2$. The projected zenith angle distribution of the shower primaries could be approximately represented by ${cos}^m\theta$, where $m$ was in the range 8 to 10. Since the measurements were made at 680 g/${\mathrm{cm}}^2$ atmospheric depth, this corresponds to an absorption mean free path in air of 70 to 90 g/${\mathrm{cm}}^2$. The flux of particles capable of producing these high energy showers was found to be (1.7±1) × ${10}^{-6\mathrm{}}$ particles ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ ${\mathrm{sterad}}^{-1\mathrm{}}$. This value, when compared with the flux of the primary protons at the top of the atmosphere, yielded an absorption mean free path of 71±5 g/${\mathrm{cm}}^2$. Application of the Gross transformation changed this value to 77±5 g/${\mathrm{cm}}^2$. The large mass of the gold nucleus plus the presence of two mean free paths of material inside the chamber made it very unlikely that only a small fraction of the energy of the primary particles be lost in the cloud chamber.