  A new method for non-intrusive estimation of the depth of buried radioactive
waste have been developed. The method is based on an approximate
three-dimensional relative attenuation model that exploits the variation in the
intensities of the radiation image obtained on the surface of the material in
which the radioactive source is buried. Experimental results using an organic
liquid scintillator detector showed that the method is able to estimate the
depth of a 329 kBq Cs-137 radioactive point source buried up to 12 cm in sand.
