  Dismantling nuclear power plants entails the production of a large amount of
contaminated (or potentially contaminated) material whose disposal is of
crucial importance. Most of the end products have to be stored in special
repositories but it can happen that some of them are slightly contaminated or
not contaminated at all, making it possible to free release them. One possible
approach to free release measurements uses Large Clearance Monitors, chambers
surrounded by plastic scintillation detectors that allow a decision about the
clearance of waste packages up to 1000 kg. Due to the composite nature of the
detectors in a Large Clearance Monitor, it is easy to imagine that one can
apply 3D imaging algorithms to localize radioactive sources inside a waste
package. In this work we will show how a special algorithm that maximizes the
conditional informational entropy allows decisions about the clearance of
portions of the sample.
