Background radiation spectrum and its influence on low level activity measurements in the environmental samples

The paper discusses the variations in the background gamma radiation spectrum as an important parameter in low level activity measurements. The background radiation spectrum has been recorded from 1993 to 1995 on two HPGe detectors under equivalent environmental conditions but placed in differently constructed Pb cages. The results indicate that when one estimates low level activities of natural radionuclides in the environmental samples, background radiation can be a significant source of error, due to inadequate shielding or long counting time intervals. Special attention should be paid to the seasonal variations of the lines of Bi-214 and Pb-214, while errors due to intensity variations in K-40, U-235 and Th-232 lines in the spectrum are within the total error of the method. Errors in intensity estimations in low and high energy range of -the background spectrum should not be neglected, too. (author)