Year
2001
Abstract
The operation of dismantling have needed the emergence of new concepts of measurements in order to prepare and to follow the operations of sanitation. The ALARA principal is particularly involved in the knowledge of the conditions of sanitation. Measurement of dose rate is recognized now as important but insufficient to reflect the radiological status. Gamma camera and gamma spectroscopy become an important part of the solutions to get this best status knowledge, one condition being that complex geometry of measurement could be modelized accurately in reasonable time for the measurement efficiency determination. The development performed recently by the French Atomic Commission (CEA), Cogema and Eurisys Mesures had for main subject the realization of this kind of tool of fast and accurate modelization, the Mercure/Pascalys modelization software. Dedicated to gamma spectroscopy purposes, the modelization is performed including the geometry, the chemical compositions and the characteristics of the detector for global measurement efficiency. The choice of the calculation code has been fundamental for the best compromise between the accuracy and the time of calculation. Direct line-of-sight point kernel Mercure code developed by the French Atomic Commission has represented this best compromise with current calculation time of a few minutes. Recent works has shown differences in results between Mercure and MCNP for the lowest energy especially below 200 keV. The impact of the coherent diffusion have been demonstrated as part of these differences. The modelization of the intrinsec efficiency of the Ge detector has also demonstrated its impact. The present paper show these results (both simulation and experimental) and their corresponding conclusions.