Study of the Charge Spectrum of Extremely Heavy Cosmic Rays Using Combined Plastic Detectors and Nuclear Emulsions

Tracks of 99 nuclei with $Z>\mathrm{}36\mathrm{}$ have been analyzed in a stack of Lexan polycarbonate, cellulose triacetate, and nuclear emulsion launched from Palestine, Texas, with an area-time factor of 900 ${\mathrm{m}}^2$ h. Although the mean deviation in charge assignment between plastics and emulsion was ∼3 units, there was no systematic variation. One nucleus with charge estimated to be $Z\approx 96$ ($\beta \approx 0.95$) was identified in all three detectors. Combining all available data, 33 events have been found with $Z>\mathrm{}70\mathrm{}$, giving for the important ratio $\frac{\mathrm{}(Z>\mathrm{}83\mathrm{})\mathrm{}}{\left(70\mathrm{}\leqq Z\leqq 83\right)}$ the value ∼0.3. The weakness of the Pb peak relative to the Pt peak indicates that little radioactive decay of the transbismuth nuclei has occurred. These results favor supernova explosions within the galaxy as the major source of cosmic rays and suggest that their average lifetime is less than ${10}^7$ yr.