A paper-tape digital recording system is described which has been used to determine the isotopic abundance ratios of strontium from geologic samples. The system costs less than $10 000 and has proved to be highly reliable during its three years of operation. More than 600 analyses have been recorded and the results processed by an IBM-360 computer. This procedure has improved the precision of analyses from this laboratory by a factor of two. Over a period of 11 months, 16 measurements on the M.I.T. strontium carbonate standard gave a mean value for (87Sr/86Sr)n = 0.70797 ± 0.017%. The uncertainty En the results is the standard deviation of the analyses with the 86Sr/88Sr value normalized to 0.1194. Over shorter periods of time considerably better precision is indicated.

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