AR37/AR39 Ratios in Meteorites : the Flux and Heliocentric Radial Gradient of Galactic Cosmic Rays during the Last Two Solar Cycles and the Millennium
Abstract
Ratios between the cosmogenic Ar-37 and Ar-39 activities in meteorites are used to estimate the long-term heliocentric gradient in galactic cosmic ray intensities, and changes in intensities between the last two solar cycles and the last millenium. Comparisons of past galactic cosmic ray intensities deduced from sunspot records with experimental measurements of the Ar-37/Ar-39 ratios in the Fe plus Ni phases of 19 meteorites fallen between 1959 and 1977 indicate a 20 percent greater flux over the past millenium, when Ar-39 was formed, than over the past two solar cycles, when the measured Ar-37 was produced. Results are also consistent with a radial gradient in galactic cosmic ray flux of less than 5 percent/AU between 1 and 2.8 AU for particle energies of 1 to 2 GeV. An important decrease in galactic cosmic rays in the vicinity of the earth during the solar maximum of 1969-1971 is also indicated.
- Publication:
-
International Cosmic Ray Conference
- Pub Date:
- 1981
- Bibcode:
- 1981ICRC....3..242B
- Keywords:
-
- Argon Isotopes;
- Cosmic Rays;
- Galactic Radiation;
- Meteoritic Composition;
- Solar Cycles;
- Radiant Flux Density;
- Radioactive Age Determination;
- Lunar and Planetary Exploration;
- ARGON ISOTOPES;
- COSMIC RAYS;
- GALACTIC RADIATION;
- METEORITIC COMPOSITION;
- SOLAR CYCLES;
- RADIANT FLUX DENSITY;
- RADIOACTIVE AGE DETERMINATION