Cosmic ray exposure ages of chondrites, pre-irradiation and constancy of cosmic ray flux in the past
Abstract
A systematic calibration of the production rate of one specific cosmic-ray-produced nuclide in chondrites, that of 21Ne, was achieved by using four independent methods: P 21(1.11) = 0.507 ± 0.039, 0.302 ± 0.013, 0.312 ± 0.017and0.292 ± 0.019 (in units of 10 -8 cm 3 STP/g My) based on 26Al-age, 53Mn-age, 81Kr- 83Kr and 22Na- 22Ne methods, respectively. These production rates are all normalized to a shielding parameter ratio 22Ne/ 21Ne= 1.11 and to the chemical composition of L chondrites. The results obtained by the latter three methods are in good agreement, but they disagree in a systematic way with the 26Al-age calibration. Based on these results, we recommend a value P 21(1.11) = 0.31 and a production rate equation:P 21 = 4.845 P 21 (1.11) F[21.77( 22Ne/ 21Ne) - 19.32] -, where F = 1.00 for L and LL, and F = 0.93 for H chondrites, for the calculation of cosmic ray exposure ages on the basis of Ne concentrations. In an attempt to assess possible causes for this discrepancy, we discuss the 26Al half-life measurements, we evaluate effects resulting from pre-irradiation of meteorites, and we discuss the evidence regarding the constancy of the cosmic ray flux in the past, in the light of some recent astronomical observations.
- Publication:
-
Earth and Planetary Science Letters
- Pub Date:
- October 1980
- DOI:
- 10.1016/0012-821X(80)90126-0
- Bibcode:
- 1980E&PSL..50..156N
- Keywords:
-
- Chondrites;
- Cosmic Rays;
- Meteoritic Composition;
- Neon Isotopes;
- Nuclides;
- Particle Production;
- Abundance;
- Chemical Composition;
- Particle Interactions;
- Radioactive Isotopes;
- METEORITES;
- CHONDRITES;
- COSMIC RAYS;
- EXPOSURE AGES;
- PRODUCTION RATE;
- FLUX;
- DATA;
- CATALOGS;
- ISOTOPES;
- AGES;
- CALIBRATIONS;
- ISOTOPIC RATIOS;
- SODIUM;
- NEON;
- HELIUM;
- ARGON;
- KRYPTON;
- PHOSPHORUS;
- CONCENTRATIONS;
- ALUMINUM;
- MANGANESE;
- SATURATION;
- MODELS