Uncertainty analysis in environmental radioactivity measurements using the Monte Carlo code MCNP5

Abstract

ElsevierGallardo Bermell, S.; Querol Vives, A.; Ortiz Moragón, J.; Ródenas Diago, J.; Verdú Martín, GJ.; Villanueva López, JF. (2015). Uncertainty analysis in environmental radioactivity measurements using the Monte Carlo code MCNP5. Radiation Physics and Chemistry. 116:214-218. doi:10.1016/j.radphyschem.2015.05.023. Uncertainty analysis in environmental radioactivity measurements using the Monte Carlo code MCNP5 ABSTRACTHigh Purity Germanium (HPGe) detectors are widely used for environmental radioactivity measurements due to their excellent energy resolution. Monte Carlo (MC) codes are a useful tool to complement experimental measurements in calibration procedures at the laboratory. However, the efficiency curve of the detector can vary due to uncertainties associated with measurements. These uncertainties can be classified into some categories: geometrical parameters of the measurement (distance source-detector, volume of the source), properties of the radiation source (radionuclide activity, branching ratio), and detector characteristics (Ge dead layer, active volume, end cap thickness). The Monte Carlo simulation can be also affected by other kind of uncertainties mainly related to cross sections and to the calculation itself. Normally, all these uncertainties are not well known and it is required a deep analysis to determine their effect on the detector efficiency. In this work, the Noether-Wilks formula is used to carry out the uncertainty analysis. A Probability Density Function (PDF) is assigned to each variable involved in the sampling process. The size of the sampling is determined from the characteristics of the tolerance intervals by applying the Noether-Wilks formula. Results of the analysis transform the efficiency curve into a region of possible values into the tolerance intervals. Results show a good agreement between experimental measurements and simulations for two different matrices (water and sand).

Stochastic simulation study of HPGe detector response and the effect of detector aging using Geant4

“…In a sep a rate work, Dryak and Kovar [20] used a collimated pho ton beam of 59.5 keV from an Am-241 source from var i ous in ci dence an gles on the front face of an HPGe de tec tor to de ter mine the ef fec tive thickness of the dead layer. Like wise, many re search ers found it nec es sary to op ti mize the dead layer thick ness in or der to re move dis crep an cies be tween ex per i mental ob ser va tions and cor re spond ing Monte Carlo sim ulated val ues [21][22][23][24][25][26][27][28][29][30][31].…”