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Cet article s'adresse aux laboratoires de mesure de radioactivite mobilisables dans le contexte d'un accident nucleaire ou radiologique, survenant en France ou a l'etranger. Il constitue une aide a la preparation des moyens et des equipes en vue de faire face a une situation post-accidentelle. Son objectif est de favoriser la production, dans un delai adapte a la situation, de resultats d'analyse fiables et exploitables par le demandeur. Il aborde l'organisation generale des laboratoires et la metrologie.

Spatial distributions and temporal changes of radioactive fallout released by the Fukushima Dai-ichi Nuclear Power Plant accident have been investigated by two campaigns with three measurement schedules. The inventories (activities per unit area) of the radionuclides deposited onto ground soil were measured using portable gamma-ray spectrometers at nearly 1000 locations (at most) per measurement campaign. Distribution maps of the inventories of (134)Cs, (137)Cs, and (110m)Ag as of March, September, and December 2012 were constructed. No apparent temporal change of the radionuclide inventories was observed from March to December 2012. Weathering effects (e.g., horizontal mobility) were not noticeable during this period. Spatial dependence in the ratios of (134)Cs/(137)Cs and (110m)Ag/(137)Cs were observed in the Tohoku and Kanto regions. The detailed maps of (134)Cs and (137)Cs as of September 2012 and December 2012 were constructed using the relationship between the air dose rate and the inventory.