ESTIMATION OF ELEMENTAL ABUNDANCES OF HEAVY COSMIC-RAY PRIMARIES AT THE TOP OF THE ATMOSPHERE USING PLASTIC EMULSION CHAMBER AND THE DERIVED SOURCE SPECTRUM FROM THE STEADY-STATE LEAKY BOX MODEL

Final results of the experiment for the estimation of charge abundance s using plastic emulsion chamber consisting of CR-39 (HCB) and Fuji ET -7B nuclear-emulsion sheet, launched from Alice Springs for 32 hours a t an atmospheric depth of 9.8 g cm(-2) is presented. The latest long h our etching technique was used for track detection in plastics. The es timated reduced etch rate distribution presented was based on 2968 mea sured track diameter data in CR-99 (HCB) stacks. The observed charge s pectrum from the reduced etch rate distribution was duly corrected for the top of the atmosphere by adopting the conventional formulation fo r cosmic-ray propagation along with the latest modified partial cross- sections for A-A collisions after Tsao et al. The average value of the observed energy of the 77 very heavy primaries was estimated from the opening angle measurements of alpha fragments in Fuji ET-7B nuclear e mulsion and was found to be 5.01 GeV/n which comes out to be 8.2 GeV/n , when corrected for the top of the atmosphere due to propagation in t he residual atmospheric depth. The measured integral fluxes for NeMgSi and Fe groups above 4 GeV/n have been compared with the global data s urveyed by Ichimura et al. Our results on element/Si and element/Fe ha ve been compared with the HEAO-3-C2 data after Englemann et al. Using SSLB model, the source abundance is derived from the observed result a nd that was compared with the results of Juliusson et al., Lezniak and Webber and Garcia-Munoz et al.