Background radiation reduction for a high-resolution gamma-ray spectrometer used for environmental radioactivity measurements

• The use of passive shielding to improve the MDA for HPGe detector is demonstrated.
• The advantages of a double shielding are presented.
• The MDA improved by at least 13-fold for 137Cs for maximum shielding configuration.

A detailed analysis is presented of background radiation spectra for a high-resolution gamma-ray spectrometer used to measure environmental radioactivity, for various shielding configurations. The main goal is to improve the detection limits of low-level activity measurements by reducing the background as much as possible. Passive shielding configurations are used to decrease the total background counting rate by adding new layers. Subsequently, for the maximum shielding configuration, the Minimum Detectable Activity (MDA) is improved by at least 13-fold for 137Cs, 8-fold for 214Bi (609.31 keV), 7-fold for 40K and 5.5-fold for 208Tl (2614.53 keV). A reduction factor of 240 for the 137Cs peak (counting rate) at maximum shielding and an insignificant peak for this radionuclide was determined. For other radionuclides, peaks below the detection limit of the detector system were also found. These results show that the shielding was successful in reducing and removing peaks from the background spectrum.