EVIDENCE FOR ANOMALOUS AG-107 AND AG-109 COMPOSITIONS IN IRON-METEORITES

We have applied an in-situ method of Accelerator Mass Spectrometry (AM S) to determine Ag-107 and Ag-109 compositions in several groups of ir on meteorites and we have observed extreme variations of Ag-107 and Ag -109 counting rates from those samples as a function of measurement se quence. In contrast, no significant variation in the counting rate of Pd-108 has been seen. These data do not necessarily imply anomalous is otope ratios, and may be due to the incidence of minute inclusions in diverse geometric forms and orientations, and with variable content of either or both Ag isotopes. The results could, however, be attributed to the preservation of presolar grains at sub-mu m scales in iron met eorites. To test this possibility, a method of simultaneous AIMS measu rement of the isotopes must be developed.