CLOUD CHAMBER ANALYSIS OF COSMIC-RAY SHOWERS UNDER 10 TO 23 CM OF LEAD

A C T * A countc?r-oontrolled cloud chaipbcr Htudy of different typoR of fthowors in Pb, under 10 to 23 cm.Has been made to investi^tc the controversial existc'nt'o of higher maximum in Rossi curve and its probable origin.The chamber and the counters in triple coincidence were specially arranged to det-ect the forn|ation of a charged pair or part icle by the decay or dissociation of an unstable neutral pafticle in air under the Pb absorber.Tlui triple coineidence frequency rises by about 23% ovt^ the backgrouiul under about 16cm. of Pb.Analysis of the shower photographs, howevor, shows that this rise is largely due to a single charged particle mostly mesons coming from the top absorber which by subse(|uent knock-on process or otherwise produces the triple coincidence.These singles may aiicount for about 12% of the total rise.About 10% of the total rise may be attributed to mixed meson and meson showers.Analysis of shower photographs by neutral component shows that out of about thousand photographs we have obtained only one penetrating pair with its af>ex in air undi^r 16 cm. of Pb and this may be due to a V-ty]^o of decay.Rut we have obtained many otlu^r photogra])bs mainly under 15 to 20 cm. of Pb which show isolated pairs of very low f^nor^y (inferred from range and angular divergence) formed by a neutral component.Thesi* type of showers may account for the remaining 6 to 8 % of the total rise at the second maximum.The origin of such pairs particularly in some photographs, by photon or indirectly by neutron is not very clear.There is a third possibility that theses j>airs are producc'd by the d«H*ay of ii neutral part icle of very low mass.This possibility may further bo checked by a mult iph' plate chainber as wo propose to do. 1 N H () D V C T ] O N