Evaluation of accuracy of response matrix method for environmental gamma ray analysis

The response matrix was improved by re-calculation of its essential constants and the improved matrix equation was evaluated for its accuracy on dose rates and on concentrations of K, U, Th radioactivity in comparison with other methods like G(E) function. Obtained values with resolution change of 40K indicated that, for accurate evaluation of K, U, Th concentrations in a certain area, optimal values were recommended to be selected where Xsi/Xcf was close to 1 by the resolution change. For measurement of U concentration with about 10% reproducible accuracy, around 8 or 15 Gy gamma ray dose was necessary for 3''φx 3'' and 3'' spherical NaI(Tl) detectors or 2''φx 2'' one, respectively. For dose rate alone, only 2 nGy dose was found necessary with 4-5% accuracy in those three detectors. For dose rate, the accuracy was found low in 14-19% relative to the G(E) function method but the matrix was concluded to have no big problem in a practical mean. (K.H.)