Cosmogenic nuclides in recently fallen meteorites: Evidence for galactic cosmic ray variations during the period 1967--1978
Cosmogenic radionuclides were measured on 48 fragments of 24 meteorites which fell between 1967 and 1978. Nondestructive gamma counting techniques were used to obtain data on /sup 7/Be, /sup 46/Sc, /sup 48/V, /sup 51/Cr, /sup 54/Mn, /sup 56/Co, /sup 57/Co, /sup 58/Co, and /sup 60/Co on at least some of the samples. Sodium 22 and /sup 26/Al measurements are reported on all 48 samples. In addition, new rare gas data and exposure ages are reported for the meteorites Guibga, Gorlovka, Dhajala, Louisville, Acapulco, Jilin, Kabo, Alta-Ameen, and Canon City. The cosmogenic radioisotope and rare gas data are interpreted in terms of a time dependent modulation of galactic cosmic rays spanning one full 11 year sun spot cycle. Special attention is given to the data on /sup 22/Na, /sup 46/Sc, /sup 54/Mn, and /sup 48/V with either /sup 26/Al or /sup 22/Ne//sup 21/Ne used to provide a shielding correction. The shielding normalized data using the /sup 26/Al method appear to correlate well with calculated production rates scaled against the Deep River neutron monitor. The data for the four isotopes are consistent with a production rate variation of a factor of 2.5--3 between solar maximum and solar minimum for sun spot cycle 20. These data demonstrate that the production rates of cosmic ray-produced nuclides in meteorites vary considerably according to modulation by the 11-year solar cycle and support the concept that variations of solar-modulated, cosmic ray flux of similar magnitude have occurred over much longer time periods.
- Research Organization:
- Battelle Pacific Northwest Laboratories, Richland, Washington 99352
- OSTI ID:
- 6236982
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 87:B7
- Country of Publication:
- United States
- Language:
- English
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