RADIUM ISOTOPES AND RN-222 IN SHALLOW BRINES, KHARAGHODA (INDIA)

The concentrations of Ra isotopes Ra-224, Ra-223, Ra-228 and Ra-226) and Rn-222 have been determined in brines from Kharaghoda, western India. The Ra isotopes concentrations in these samples are orders of magnitude higher than that reported in potable groundwaters. The Ra-224 activities lie between 28 to 277 dpm per kg; about 4% to 96% of that expected from its production, calculated using Rn-222 as a recoil flux monitor. The low [Ra-224/Rn-222] activity ratios are typical of less saline brines. Retardation factors for Ra in these brines, derived from the Rn-222-Ra-224-Ra-228 system and based on a reversible exchange model, are in the range of about 0.3-114. These values are 3-4 orders of magnitude lower than that in potable groundwaters. The residence time of Ra in Kharaghoda brines is approximately one day. Our data suggest that in briny aquifers Ra is considerably less 'particle-reactive' than in potable groundwaters. The retardation factor for Ra shows a strong negative correlation with salinity. This anticorrelation suggests that salinity would play a crucial role in determining the mobility of Ra and its geochemical homologues through groundwater systems.