Low level activity determination by means of gamma spectrometry with respect to the natural background fluctuation

• Long term study of background peaks and integral counts.
• Background fluctuation cause differences in low level activity determination.
• Background fluctuation influence MDA calculation.

The determination of low level activities of natural radionuclides from the uranium and thorium series by gamma-spectrometry faces the problem of proper natural background subtraction. Background fluctuation can cause differences in activity determination. Also the minimum detectable activity (MDA) of natural and artificial radionuclides can be influenced by background fluctuation. In this paper, results of the background fluctuation of shielded HPGe detectors with relative efficiency of 50–150% are presented together with the assessment of its influence on the determination of natural and artificial radionuclides.