Cosmogenic radioactivities in the Peace River and Harleton chondrites

The results of measurements of cosmogenic radionuclides in the Peace River and Harleton chondrites shortly after their falls are reported. Activity ratios of short- and long-lived nuclides are compared with ratios observed in other freshly fallen meteorites. Long-term temporal constancy of the cosmic-ray flux within 50% is supported, and a spatial variation of cosmic radiation of less than a factor of 2 throughout meteoritic orbits is indicated. The 11-year solar cycle does not appear to have had any significant effect on activities with half-lives of the order of about a year, such as Mn54 and Na22, except for Co60 in Harleton, which seems to be high in our specimen as a result of solar-particle effects. The activities are compared with thick-target production cross sections.