Unfolding method for surface activity density map reconstruction from ambient dose equivalent rate measurements based on solution of Fredholm equation of the 1st kind

A mathematical method has been developed for determining surface activity density maps from ambient dose equivalent rate measurements on a site with buildings, taking into account the shielding effect of the buildings by using a visibility matrix. The relationship between surface activity density and ambient dose equivalent rate is described through the Fredholm equation of the 1st kind and is numerically solved with a Tikhonov regularization. Use of the visibility matrix and raster cells made it possible to solve the Fredholm equations in barrier geometry to restore the density of the surface radionuclide contamination based on the ADER measurement. Method was used to restore locations of contamination with 137Cs and its activities for the Andreeva Bay nuclear legacy site. The proposed method can be applied in the process of decontamination of radioactively contaminated territories, in particular during the remediation of the Andreeva Bay.