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The mapping of gamma source radiation emission in a nuclear plant is an important safety factor required in a variety of circumstances: 1. Search for radioactive sources. 2. Surveillance of stored radioactive materials. 3. Monitoring of radioactive waste circuits and nuclear fuel reprocessing. 4. Preparation for work and cost assessment in a nuclear plant. 5. Definition of decontamination, dismantling, and decommissioning of a nuclear plant. 6. Initial strategy in the event of incident or accident.
A remote gamma ray mapping process has been developed by SPS/CEA/SACLAY. It uses the "pinhole camera" principle, a precursor of photography. It consists essentially of a radiation-proof box, with a small orifice, placed opposite sensitive emulsions.
An initial conventional photographic-type emulsion photographs the area. A second photographic emulsion shows up the gamma radiations. The superimposition of the two shots gives immediate information concerning the precise location of each source of radiation in the area observed.
To facilitate presentation and to improve the accuracy of the results of radiation level mapping, the films are processed digitally. The processing assigns a color scale to the various levels of observed radiation. Taking into account physical data and standard parameters, it enables estimation of the dose rate.
The device is portable. Its compactness and fully independent nature make it suitable for use anywhere. It can be adapted to a remote automatic handling system, robot, or the like so as to avoid all operator exposure when the local dose rate is too high.
remote gamma-ray mapping, pinhole gamma camera, multisource locations, multisource dosimetry, dose rate, radioactive source
CEA-IRDI-DERPE, Gif sur Yvette,