Heavy Nuclei andαParticles between 7 and 100 Bev/Nucleon. I. Interaction Mean Free Paths and Fragmentation Probabilities

In a stack of nuclear emulsion exposed to the cosmic radiation near the geomagnetic equator, 540 tracks of heavy nuclei were located in a systematic scan and followed along the track. Twenty-two interactions of light ($3<~Z<~5$), 218 of medium ($6<~Z<~9$), and 99 of heavy ($Z>~10$) nuclei have been found. The average energy of the nuclei in this experiment was about 20 Bev per nucleon. The interaction mean free paths for all charge groups are in reasonably good agreement with results obtained at lower energies, indicating that the mean free path is independent of energy within the limits of error. In addition, all the $\alpha$ particles originating in fragmentations of heavy nuclei have been followed. The mean free path of $\alpha$ particles resulting from fragmentations is again in agreement with results obtained at lower energies. The same is true for the fragmentation probabilities.