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Description
A search for short-lived ^10^Be in 21 calcium-aluminum-rich inclusions (CAIs) from Isheyevo, a rare CB/CH chondrite, showed that only 5 CAIs had ^10^B/^11^B ratios higher than chondritic correlating with the elemental ratio ^9^Be/^11^B, suggestive of in situ decay of this key short-lived radionuclide. The initial (^10^Be/^9^Be)_0_ ratios vary between ~10^-3^ and ~10^-2^ for CAI 411. The initial ratio of CAI 411 is one order of magnitude higher than the highest ratio found in CV3 CAIs, suggesting that the more likely origin of CAI 411 ^10^Be is early solar system irradiation. The low (^26^Al/^27^Al)_0_ [<=8.9x10^-7^] with which CAI 411 formed indicates that it was exposed to gradual flares with a proton fluence of a few 10^19^protons/cm2, during the earliest phases of the solar system, possibly the infrared class 0. The irradiation conditions for other CAIs are less well constrained, with calculated fluences ranging between a few 10^19^ and 10^20^protons/cm2. The variable and extreme value of the initial ^10^Be/^9^Be ratios in carbonaceous chondrite CAIs is the reflection of the variable and extreme magnetic activity in young stars observed in the X-ray domain.
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