Improvement of quality in the evaluation of radium isotopes 224,226,228 Ra in oil scale samples

Elevated concentrations of the radium isotopes 224,226,228 Ra exist in the scale and produced water in oil exploration. The activity concentration of 226 Ra was calculated from 186.2 keV peak with no usual spectral interference of 185.7 from 235 U. The activity concentration of 228 Ra was calculated from its first daughter product 228 Ac using the 911.2 keV gamma rays since it is a pure beta emitter. The activity concentration of 224 Ra was calculated from 212 Pb using the 238.6 keV gamma-ray and the secular equilibrium equation with 228 Ra. The IAEA 448 (oil contaminated field soil) reference material was used as a quality control for 226,228 Ra and but was unreliable for 224 Ra using 212 Pb.