A cosmic ray jet in the 10¹² electron volt energy range

Summary

A 22.4 litre stack of emulsions was exposed in Minnesota during Septemper 1956 in a balloon flight at 116000 feet. The emulsion stack, which was flown in a cooperative experiment with University of Bristol, weighed 200 lbs and had dimensions of 16 in. × 12 in. × 7 in. The largest jet so far found by naked-eye scanning traversed the entire Minnesota half of the stack with a total lenght of 26 cm. The primary interaction is a 6 + 1α star. In the nine radiation lengths of the Minnesota portion of the stack, the jet multiplied from nine particles, mainly in two cores, to 8 000 particles. The electromagnetic, cascade appeared to be initiated by several γ rays probably from the decay of two neutral mesons. The electromagnetic cascade was still increasing in numbers after nine radiation lengths. At approximately 23 cm from the primary interaction, the primary particle produced a meson jet in the core of the electromagnetic cascade. The meson star was classified as 4 + 80p. The angle containing half of the 80 minimum ionization particles was 3.10^-4 rad. The energy of the primary α-particle is estimated to be ⩾ 10¹⁵ eV. The energy in this event which appeared in electronic component is approximately 10¹⁴ eV.