ABSTRACT

We have examined the elemental abundances of noble gases in graphite and diamond exposed to a glow discharge in a mixed noble gas atmosphere. The heavier noble gases were much enriched both in the diamond and the graphite compared to samples merely exposed to ambient gases without discharge. The noble gases were released below 800°C for all graphite samples, regardless of the applied voltage. Considerable amounts of heavy noble gases were released at higher temperatures from the diamonds exposed to higher voltages, suggesting that noble gases were more tightly implanted into the diamond than into the graphite. These results are relevant to the origin of noble gases in ureilite if carbon materials were of vapor growth origin in the solar nebula. Noble gases could have been contained in the diamond but not in the graphite, because of the higher retentivity of noble gases in diamonds at their formation temperatures.