No abstract

Gamma-ray spectroscopic measurements of low-level environmental samples require the reduction of the background as low as practicable. In the present work, we investigate the advantages of adding Hg passive shielding inside a low-background Pb-shield to further reduce the background radiation. The background count rate achieved by the Pb-shield alone over the energy interval from 25 to 2700 keV, amounts to 8.4 × 10 −4 counts/s.keV which is ∼ 1.5% of the normal background. The introduction of Hg-shield adds another 15% reduction. On the average, the Hg-shield suppresses the net peak areas of X-and gamma-rays to < 3 and 1% of the normal background, respectively. On the other hand, the reduction in the count rate of these peaks due to the addition of Hg-shield varies according to the energy. The measurements showed no evidence of the presence of cosmogenically produced 194 Hg in the measured spectra. An additional 2% reduction was achieved by using neutron moderators.