Decision threshold and detection limit in low-levels of radioactivity measurements

Objective: The calculation methods for decision threshold and detection limit of radioactivity measurement for low background were discussed. Methods: Based on the data from 18 biological samples measured by Alpha spectrometer, formulas of decision threshold and detection limit given in RSG1.2 (IAEA), NUREG 1576 (USA) and AQ48 (IAEA) were used and discussed. Results: Parts of the results decided by these three kinds of formulas would be entirely different, which indicated that formulas of NUREG 1576 and AQ48 were much more conservative than the formulas of RSG1.2 for low background counts (as < 100). Conclusion: To ensure the reliability when judging the measured data, formulas of decision threshold and detection limit must be chosen according to the actual condition (such as background counts, background count time and gross count time, etc.), especially in low-level radioactivity measurements. (authors)