ABUNDANCE OF ACTINIDE ELEMENTS IN THE GALACTIC COSMIC RADIATION.

The Bristol-Dublin balloon borne ultra heavy cosmic ray experiments which employed solid state nuclear track detectors indicated an abundance ratio (88 less than equivalent to 2 less than equivalent to 100)/(74 less than equivalent to 2 less than equivalent to 87) which was more than an order of magnitude greater than that measured for solar system material. The recent Ariel 6 data does not show any significant enhancement for Z greater than equivalent to 88 (actinides) and the results from the HEAO-3 experiments are consistent with a source of solar system composition. A re-assessment of the actinide abundance found in the early balloon borne experiments, in the light of our recent studies on the effect of detector temperature on track response in solid state nuclear track detectors, indicates a lower value than previously reported. The consequences for cosmic ray origin studies and future ultra heavy cosmic ray experiments are discussed.