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

1. 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 with a closed volume, 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 case, and the long base being designed to be placed facing the bottom of the aqueous medium, said closed volume being sealed and operable to displace said aqueous medium when immersed therein.

2. Device according to claim 1 , said material being a gas or a low density solid material that traps said gas.

3. Device according to claim 2 , the solid material having a density less than 0.1 g·cm −3 .

4. Device according to claim 1 , the long base of the truncated cone being closed by a plate comprising a central portion delimited by a tubular portion, arranged approximately perpendicular to the long base, and ribs extending radially connecting the tubular portion and said plate.

5. Device according to claim 1 , the angle of the truncated cone being between 15° and 75.

6. Device according to claim 5 , the angle of the truncated cone being on the order of 60°.

7. Device according to claim 1 , the case extending along an axis approximately perpendicular to the axis of revolution of the truncated cone.

8. System for measurement of the radiological activity at the bottom of an aqueous medium comprising:

a frame for immersion in an aqueous medium,

a measurement device supported by said frame and comprising a sealed case for a radiological detector, means forming a truncated cone with a closed volume for containing a material that allows radiation to be measured by said radiological detector by passing through it, a short base and a long base, the long base forming an input face for the radiation to be measured, the cone being assembled to said case in a sealed manner, the short base being placed on the side of the detector input face case, and the long base being designed to be placed facing the bottom of the aqueous medium, said closed volume being sealed and operable to displace said aqueous medium when immersed therein.

9. System according to claim 8 , also comprising at least one spotlight means of illuminating the aqueous medium and the bottom of this aqueous medium.

10. System according to claim 8 , the frame-comprising perforated side walls.

11. System according to claim 8 , the frame comprising at least one flange removably fixing the measurement device relative to the frame.

12. System according to claim 8 , also comprising an underwater positioning system of the frame relative to the bottom of the aqueous medium.

13. System according to claim 8 , also comprising a computer to produce a map of the radiological activity of the bottom of this aqueous medium.

14. System according to claim 8 , also comprising at least one camera to film the aqueous medium and the bottom of this aqueous medium.

15. System according to claim 8 , also comprising at least one motor displacing the measurement device relative to the frame.

16. System according to claim 8 , also comprising a remote-controlled vehicle.

17. System according to claim 8 , the frame also comprising to position the system on the bottom of the aqueous medium.

18. Method of measuring the radiological activity in the bottom of an aqueous medium, comprising:

introducing a device into the aqueous medium, the device having a sealed case for a radiological detector, means forming a truncated cone with a closed volume for containing a material that allows radiation to be measured by said radiological detector by passing through it, a short base and a long base, the long base forming an input face for the radiation to be measured, and the long base being adapted to be placed facing the bottom of the aqueous medium, said closed volume being sealed and operable to displace said aqueous medium when immersed therein;

measuring the radiological activity using the measurement device, with the long base of the truncated cone being brought close to the bottom of the aqueous medium.

19. Method according to claim 18 , also comprising the production of a map of the radiological activity of the bottom of the aqueous medium.

20. Method according to claim 18 , the aqueous medium being a lake, a sea or a river, or an estuary, or a storage pool on a nuclear site, or a sedimentary retention zone.