Effect of Location and Shielding on Gamma Radiation Background in Low Level Gamma Ray Spectrometry

Ambient gamma radiation levels due to natural and anthropogenic sources play an important role in low level gamma spectrometric measurements of different sample matrices. Minimum detection level (MDL) of a high-resolution gamma spectrometry system directly depends on the background radiation levels. The variation of background radiation level due to the location (surface level or below ground level) of the laboratory housing the gamma spectrometric system and the impact of different shielding types is discussed in this study. Relocation of the system to a below ground level laboratory significantly brought down the background induced due to cosmic components. Corresponding reduction in count rates for major gamma emitters ranged from 36 to 59%. Consequently, the MDLs for corresponding peaks improved by 20 to 36%. Improvising the lead bricks-based passive shielding for the gamma spectrometry system to circular lead ring with graded Cu+Sn lining minimised the gamma background due to streaming of gamma rays through lead bricks and reduced the overall background. The combined effect of the location of laboratory below ground level and graded lead shielding resulted in reduction of MDL of the gamma spectrometry system for major gamma peaks by 54 to 80%.