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Methode de simulation Monte-carlo pour etudier l'absorption alpha dans les fibres du filtre


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Titre du congrès :ICNTS 2008 - 24th International Conferences on Nuclear Tracks in Solids
Ville du congrès :Bologne
Date du congrès :01/09/2008

Type de document > *Congrès/colloque

Mots clés >

Unité de recherche > IRSN/DSU/SERAC/LPMA

Auteurs > GEHIN Evelyne, GERYES Tony, MONSANGLANT-LOUVET Céline

Date de publication > 05/09/2008

Résumé

  Nuclear facilities use air monitors to collect particulate matter in order to measure radioactivity in the environment or in working areas. The amount of alpha radioactivity collected on the sampling filter is frequently determined by direct alpha-particles measurement. Several factors can affect the alpha energy while passing through the filter to reach the detector. Since the burial depth of particulate matter is significant in the fiber filter, it seems that the most affecting factor on the spectra degradation is the absorption of alpha particles in fibers. When a filter spectrum is measured, a peak spreading inevitably takes place and the FWHM (Full Width of the Half Maximum) of the peak is then increased, as well as the peak asymmetry.
 MCNPX, which is based on the Monte Carlo method, is well suited for alpha spectrometry simulations and it can be used to investigate the influence of the various factors on the spectrum quality. The aim of this work is to study the absorption of the alpha particles inside the filter’s fibers with MCNPX. Different levels of aerosols burial depth in the filter are tested in order to quantify the energy loss in discretized filter thickness. The threshold depth of escaping alphas is also quantified. Besides, comparisons between simulated equivalent-filter density spectra and low filter-source density spectra, could give us an idea on the magnitude of the absorption inside the fibers of the filter. Therefore, it is possible to find the real activity value inside the filter after several analyses. This value could be compared to the measured activity by liquid scintillation technique which is a reference of the real activity collected on the filter.