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Radioactive sealed sources used in industry

The installation and use of industrial sources normally requires only that NRPA is formally notified of the planned activity. If, however, the activity of the radioactive source exceeds a certain value, then the enterprise that will be utilising the source must be approved.

For the most common sources, such as Cobalt-60, Cesium-137, Americum-241 and Krypton-85, approval is required at activity levels of 10 GBq. For Promethium-147, the  level is 10 TBq. The reader is however urged to consult the Regulations on Radiation Protection.

NRPA should also receive written notification in the event of name changes and when the radioactive source is handed in/disposed off. When turning in sources it should be kept in mind that both the transport and waste disposal of radioactive source are closely regulated.

What is an industrial radionuclide gauge?
Radionuclide gauges are devices used for taking measurements or for process control with the help of radioactivity from one or more sealed radioactive sources. Such devices normally consist of a housing containing a radioactive source and a detector.

How is the source housing constructed?
A source housing ensures shielding from radiation in all directions except that towards which the radioactive source is to be directed. For sources emitting high energy gamma radiation, lead is a common shielding material because of its great density. For radioactive sources that emit low energy gamma or beta radiation, other metals of lesser density offer sufficient shielding. The source housing normally comes with a closing mechanism that allows the user to open and close the device to the primary radioactive field. The source housing usually comes with a closing mechanism allowing the user to open or close for the primary beam (useful beam).

Examples of radioactive sources in use:

Radioactive sources. Photo: NRPA.
In the paper industry, promethium-147, which is a beta emitter, is used as a source for measuring the thickness of paper. The paper can pass freely between the units in such apparatuses and measurements may be made continually.

Radioactive sources. Photo: NRPA.
Pictured here is a Cesium-137 source which is used to measure the dry matter in liquids. Both the source housing to the right and the detector on the left are attached tightly with clamps around the pipe from which the measurements are to be taken.

Radioactive sources. Photo: NRPA.

Radioactive sources. Photo: NRPA.

Level gauges are used to check that the filling level, for example in a tank or bottle, is not under or over the established limits. In the example above, the detector will detect less radiation when the tank is full because the radiation is absorbed into the substance in the tank. The detector can in turn set off an alarm or an electric signal that will stop the filling of the tank. The radioactive isotopes Cobalt-60 and Cesium-137 are utilised in the level gauges mounted in tanks of large dimensions, whereas the gauges to measure the filling level in small bottles generally use the isotope Americum-241.

Example of a sealed source
The sealed radioactive source is quite small compared to the other equipment. The picture below shows a source capsule in the hand. This particular capsule is intended for demonstrational purposes only and does not contain radioactive material.

Sealed source. Photo: NRPA.

Who uses radionuclide gauges for permanent installation?
In Norway there are about 2500 radionuclide gauges for permanent installation spread between about 250 enterprises.