Secular variations in the abundances of heavy nuclei in cosmic rays.
The ratios of fluxes of heavy cosmic-ray nuclei [(30 </= Z </= 40)/(20 < Z </= 28), where Z is the atomic number], based on studies of meteorites and lunar samples, show little variation with time, distance in the solar system (1 to 3 astronomical units), or kinetic energy (30 to 2000 megaelectron volts per nucleon). Samples exposed for time intervals of 10(3) to 10(8) years show that the variations in the flux of 30 </= Z </= 40 nuclei relative to that of the iron group nuclei (20 < Z </= 28) have remained within the range of (1.3 +/- 0.6) x 10(-3) during the last billions of years, thus indicating a remarkable similarity in the elemental composition of sources responsible for these nuclei in the cosmic radiation.
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