Method and device for determining the radiological activity deposited in a sea bed

A device for measurement of the radiological activity in the bottom of an aqueous medium, comprising a sealed case for a radiological detector, means forming a truncated cone containing a material that allows radiation to be measured by said radiological detector to pass through it, comprising a short base and a long base, the long base forming an input face for the radiation to be measured, this cone being assembled to said case in a sealed manner, the short base being placed on the side of the detector input face, and the long base being designed to be placed facing the bottom of this aqueous medium.