Studies of cosmogenic in-situ 14CO and 14CO 2 produced in terrestrial and extraterrestrial samples: experimental procedures and applications

Abstract

We have developed an experimental procedure for quantitative extraction of cosmogenic in-situ 14C produced in terrestrial and extraterrestrial samples, in the two chemical forms 14CO and 14CO 2 in which it is found to be present in these samples. The technique is based on wet digestion of the sample in vacuo with hydrofluoric acid at 60–80°C in a Kel-F® vessel. Kel-F is a homo-polymer (chlortrifluorethylene). The procedures and the digestion vessel sizes used allow convenient extraction of 14C activity from samples of 50 mg to 50 g weight. Procedure blanks were reduced considerably by the experience gained with the system, and can be reduced further. We determined that most of the in-situ 14C activity was present in the CO phase (> 60%) in the case of both terrestrial quartz and in bulk samples of meteorites, analogous to the case of in-situ production of 14C in ice. Some results of measurements of 14C activities in meteorites and in terrestrial samples are presented. The latter include several samples which have been studied earlier for in-situ 10Be (and 26Al) concentrations, and allow us to determine relative 14C and 10Be production rates in quartz.