On the charge and energy spectrum of heavy primaries

Summary  The relative abundance and energy spectrum of heavy primaries in the cosmic radiation were derived using 529 tracks found in two stacks flown at high altitude at a mean geomagnetic latitude of 46° North. The amount of atmosphere and of packing material above the scanned sections of both stacks was 17 g/cm2. A good resolution was obtained in the range 3 ≤ Z ≤ 10, while in the range Z > 10 the uncertainty was ▵Z = ± 1. In order to check the resolution between boron and carbon, gap-length measurements were made on 65 boron and carbon tracks. The results of the two methods are in good agreement. All tracks were traced through the stack and a total of 331 nuclear interactions found, in order to derive the interaction mean free path and the fragmentation probabilities. The results on the relative abundance of the three charge groups (light 3≤Z≤5 (L), medium 6≤Z≤9 (M), heavyZ ≥ 10 (H)) on a total of 242 tracks whose angle of incidence to the vertical was less than 30° are the following:   Flight altitude Top of the atmosphere N 1/N M 0.46 ± 0.07 0.30 ± 0.09 N H N M 0.40 ± 0.04 0.51 ± 0.11 To obtain the energy spectrum three types of measurements on 275 tracks were made: a)relative track to track scattering on the α-particles ejected in the interactions. b)mean opening angle of fragmentation products. c) multiple scattering on a few very flat primary tracks. The integral spectrum in the range 1.5 GeV÷100 GeV agrees fairly well with a power law of the type:N(E) =C/m 0 c 2+E) n , withn = 1.54 −0.13 +0.16