Parametric study of shell-source method for calibrating radwaste radioactivity detection systems

This work presents an improved mathematical algorithm coupled with the Monte-Carlo computer code EGS4 and the Moenʹs semi-empirical method to theoretically and parametrically investigate the feasibility of using the shell-source method to calibrate the Q2 detection system. According to the calculated results, approximating the detector by a point detector only leads to a negligible effect on the calibration inaccuracy. The calculated results also indicate that the calibration inaccuracy caused by introducing the shell-source method is attributed primarily to the inaccuracy arising from the outermost shell, and this phenomenon becomes more prominent for lower photon energies and higher attenuated radwaste. The sensitivity of the shell-source method is significant for a change in detector radial positions, particularly for highly attenuated radwaste. However, it is negligible for a change in detector axial positions within the calibration drumʹs height. In addition, the results obtained from including a 0.2 cm iron wall thickness in simulating the calibration drum demonstrate that the calibration inaccuracies for both fiberboard insulation and sand radwaste are significantly reduced only at low photon energies. Further, investigating the effect of non-uniform versus uniform radwaste distributions on the calibration inaccuracy reveals that the effect decreases with a decreasing radwaste attenuation ability, implying that the Q2 detection system can be used for lightly attenuated radwaste.