39Ar recoil and the apparent persistence of the presolar age of an Allende inclusion

This is a report on the isotopic composition of argon found in neutron-irradiated quartz ampoules which contain samples of Allende coarse-grained inclusions or aluminium wrap only, and of argon released from one of these inclusions by stepwise heating. Besides atmospheric argon all ampoules contain, with varying concentrations but in constant proportions, 38Ar from Cl and 39Ar from K corresponding to Cl/K approx.= 1. No 39Ar which has recoiled out of the samples and no argon which has diffused out of the samples has been observed in the ampoule gas. The analysis of the isotope variations of argon released by stepwise heating from a sample of inclusion 18 yields an apparent 40Ar-39Ar isochron age of 4.85 AE. A re-analysis of argon from another sample of the same inclusion dated earlier yields the same result. Thus inclusion 18 contains more radiogenic 40Ar than can be accounted for by 40K decay during 4.53 AE. (orig.)