Measurement of naturally occurring radioactive materials, 238U and 232Th-part 3: is efficiency calibration necessary for quantitative measurement of ultra-low level NORM?

A well-calibrated and highly shielded HPGe detector with considerable relative efficiency is an efficient tool for measurement of naturally occurring radioactive material (NORM) present at ultra low-level in the environmental samples. Efficiency calibration is standard protocol required for quantitative estimation of the activity of any radioactive sample. In the present work it has been shown that in the case of ultra-low level NORM measurement, one can comfortably by pass efficiency calibration by using comparator method i.e., comparing the peak area counts of different photopeaks of standard and samples provided they are counted in same geometry and comparable composition.