FIG. 8. Log-log plot of 235U vs. 238U for boreholes 299-E33-45, 299-E33-41, and 299-E33-18. 238U is derived from 234Pa activity. The ratio of 235U:238U apparently varies from 0.04 in 299-E33-45 to 0.08 in 299-E33-18. Results for 299-E33-41 are split according to depth (shown), and are intermediate in isotopic ratios and agree with the ratios of both other boreholes. (Courtesy of S.M. Stoller Co.)