| Contamination of buildings represent a unique problem during Decontamination and Decommissioning (D&D) of nuclear facilities. It is necessary to determine the long-lived radionuclides and their respective specific activities in building materials before the right D&D decision can be made. At the same time, radiation risk of workers or potential occupants in the facility must be assessed as part of the D&D process. The goal of this project was to develop a methodology of obtaining gamma radiation flux and organ doses from in-situ gamma spectroscopy. Algorithms were developed to simulate the response functions of the HPGe detector and to convert the spectra into photon fluences. A Monte Carlo code, MCNP4C, was used to simulate HPGe detector response and to develop the conversion algorithm. The simulated spectra obtained for an HPGe detector were converted to flux using the algorithm for various different geometries. The response functions of the detector are presented in this document for the gamma energies from 60 keV to 2.2 MeV. Published fluence-to-dose conversion coefficients were used to calculate organ doses and effective dose equivalent. We then tested the theory at a 100-MeV linear electron accelerator at Rensselaer Polytechnic Institute (RPI). Samples of the activated concrete walls and floor in the target room of the Linac facility as well as some steel samples were taken to quantify the specific activities of the structures. The results show that the most important long-lived radionuclides include 22 Na, 46Sc, 54 Mn, 57Co, 60 Co, 65Zn, 152 Eu and 154Eu, depending on the location and composition of the material. The specific activities at the Linac facility range from 1.15E-01 to 765.31 μCi/Kg. The annual effective dose equivalent was assessed to be 2.44 mSv y−1 (0.244 rem y−1 ), which is about 5% of the Annual EDE limits to workers. |
