A large multiplate cloud chamber, 5 feet x 5 feet x 2 feet, was builtfor the purpose of investigating high energy nuclear interactions. Thechamber contained eleven (11) steel plates of absorbing material, totalingtwo hundred fifty-four (254) grams/(centimeter)^2.
The cross-section for the transfer of small amounts of energy byincident primary particles of high energy was obtained by direct mensurationon the stereoscopic photographic negatives. The tracks of high energycosmic ray particles were identified by observation of events in whichat least 50 Bev was observed in a high energy nuclear interaction. Thesesame tracks were searched for nuclear interactions of less than 10 Bev.
The analysis of six hundred thirty-six (636) cases yielded a meanfree path in iron for the primary particles in producing the small interactions of (4.37 ± 1.46) x 10^3 grams/(centimeter)^2. The primary particle-nucleuscross-section was 21.1 ± 7.1 millibarns, which corresponded toa primary particle-nucleon cross-section of 0.38 ± 0.13 millibarns.These events were interpreted as resulting from peripheral collisions ofthe primary particles with the nucleons of the iron nuclei.
An independent part of the analysis was the effect of the geigercounter efficiency. Results indicated an absence of bias in high energycross-section measurements which were based on the assumption that theselection of events for measuring the cross-section was independent ofthe counter efficiency. However, analysis also showed that the establishment of symmetric errors in such a cross-section is probably misleading.
