STUD YING THE INFLUENCE OF BACKGROUND SHIELDING MATERIALS ON CHARACTERISTIC PARAMETERS OF GAMMA SPECTRA USING THE MCNP4C2 CODE

Abstract

In gamma spectrometry, the low-background lead shield includes layers of shielding material used to reduce the gamma radiation background from the surrounding environment, but scattered gammas from these layers of shielding material can contribute and influence affects the characteristic parameters of the gamma spectra of interest. In this work, the MCNP4C2 code is used to simulate the gamma spectra for each case where the layers of material constituting the lead shield are removed from the inside out, including the material making the holder of the radioactive source. On the basis of the gamma energy spectra, peak-to-total ratios (P/T), peak-to-Compton ratios (P/C) in each case are calculated to determine the influence of each material layer. The results show that, with lead having a high atomic number Z, Compton scattering is reduced due to the photoelectric effect being dominant compared to copper and tin; paraffin plays an important role in the scattering process; the epoxy layer is in direct contact with the radioactive source, causing strong scattering when the source is close to the detector and gradually decreases with distance; air has low mass density, so scattering is negligible.