9:45 AM - 10:00 AM
[PPS07-10] Importance of 10Be as a key indicator of (solar) cosmic ray irradiation in the early solar system
Keywords:Beryllium-10, early solar system, cosmic ray, irradiation, CAIs, chondrules
Excesses in 10B correlated with Be/B ratios in a number of CAIs from CV chondrites [2-9] suggest the presence of live 10Be at the time of CAI formation. The inferred initial 10Be/9Be ratios are mostly within the range of (0.5-1) x 10-3, though the data are restricted to coarse-grained CAIs from CV chondrites. Recent studies including small CAIs from CH/CB chondrites [10-12] show that the initial 10Be/9Be ratios may be much higher and more variable (from ~10-4 to ~10-2), suggesting that the origin of 10Be in CAIs is spallation reactions induced by solar cosmic rays.
Data for chondrules are scarce. Sugiura (2001)  analyzed anorthite in chondrules from the Y82094 (ungrouped C3.2) chondrite and found a possible correlation between 10B excesses and Be/B ratios, but the results are not conclusive due to relatively large errors. We further conducted Be-B isotope analyses for chondrules in Y82094 chondrite using NanoSIMS at the Atmosphere and Ocean Research Institute, The University of Tokyo . Resolvable excesses in 10B are found in some of the Y82094 chondrules, but 10Be was probably not alive at the time of the chondrule formation. Some carriers of excess 10B are required in the precursor materials of these chondrules.
Here we review recent progress in Be-B isotopic studies and discuss their importance in understanding the irradiation processes in the early solar system. We will also show our some new results on Be-B systematics for chondrules from Y82094 (C 3.2) and NWA7936 (LL 3.15) chondrite.
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