The Response Function of Isocart (ortec) Gamma-ray Spectrometry System Using Monte Carlo Simulations

The routine operation and maintenance of nuclear facilities generate quantities of radioactive material in many different matrices that are packed in many different sized containers. The waste is often packaged in large containers, such as 220 l drums, because process operators find drums more economical to handle than small containers. Based on regulations, the radioactivity and the radionuclide composition of the waste should be characterized before moving, shipping offsite, burying, or placing in a storage area. The most important step of the characterization process, establishing radionuclide content, is often achieved by nondestructive assay (NDA). In this work calculation techniques useful for the calibration and evaluation of measurements of radioactive waste drums by gamma-ray spectrometry were developed. To this end, a simulation program based on GEANT 3.21 toolkit was developed to simulate the response function of ISOCART gamma-ray spectrometry system for a geometry measurement with the drum volume divided in 40 volume elements. The Monte Carlo method was applied to obtain the expected spectra in the energy range from 50 to 2000 keV, the full energy peak efficiencies and the total efficiencies for sources uniformly distributed in each of the volume elements defined within the drum as well as for the source uniformly distributed in the entire drum.