In this study, the Geant4 toolkit is used to simulate a Compton suppression system based upon a HPGe primary detector for radioactive environment such as nuclear plant accident. LaBr3(Ce) crystal is selected for the anti-coincidence secondary detector. Simulations for the detector system are performed to gain the optimal sizes for 500 keV – 1500 keV γ rays. Simulation results show that the Peak Compton Suppression Factors (Peak CSFs) increase significantly with the thickness increase of the body LaBr3(Ce) crystal from 10 to 60 mm, the Peak CSFs do not increase obviously after the thickness of the body LaBr3(Ce) crystal reaches 60-70 mm; Moreover, adding a LaBr3(Ce) crystal to the back of the HPGe detector can also improve the Peak CSFs, but adding a LaBr3(Ce) crystal to the front of the HPGe detector has little effect on improving the Peak CSFs. Finally, we simulate a variety of sources in our Compton suppression system under the optimal conditions: for Cs-137 and K-40 that decay via a single γ emission Compton suppression effects are good; for I-131 and Cs-134 that decay in cascade some improvements are still obtained.
