ASN Report 2017

291 ASN report on the state of nuclear safety and radiation protection in France in 2017 Chapter 10  - Sources of ionising radiation and their industrial, veterinary and research applications 1.1.3 Verification of physical parameters The operating principle of these physical parameter verification devices is the attenuation of the signal emitted: the difference between the emitted signal and the received signal can be used to assess the desired information. The radionuclides most frequently used are carbon-14, krypton-85, caesium-137, americium-241, cobalt-60 and promethium-147. The source activity levels range from a few kilobecquerels (kBq) to a few gigabecquerels (GBq). These sources are used for the following purposes: ཛྷ ཛྷ Atmospheric dust measurement: the air is permanently filtered through a tape placed between the source and detector running at a controlled speed. The intensity of radiation received by the detector depends on the amount of dust on the filter, which enables this amount to be determined. The most commonly used sources are carbon-14 (activity level: 3.5 megagecquerels – MBq) or promethium-147 (activity level: 9 MBq). These measurements are used for air quality monitoring by verifying the dust content of discharges from plants. ཛྷ ཛྷ Paper weight (grammage) measurement: a beta radiation beam passes through the paper and is then received by a detector. The signal attenuation on this detector gives the paper density and thus the grammage. The sources used are generally krypton-85, promethium-147 and americium-241 with activity levels not exceeding 3 GBq. ཛྷ ཛྷ Liquid level measurement: a gamma radiation beam passes through the container holding the liquid. It is received by a detector positioned opposite. The signal attenuation on this detector indicates the filling level of the container and automatically triggers certain operations (stop/continue filling, alarm, etc.). The radionuclides used depend on the characteristics of the container and the content. Generally speaking, americium-241 (activity level: 1.7 GBq), caesium-137 - barium-137m (activity level: 37 MBq) are used, as appropriate. ཛྷ ཛྷ Density measurement and weighing: the principle is the same as for the above two measurements. The sources used are generally americium 241 (activity level: 2 GBq), caesium-137, barium-137m (activity level: 100 MBq) or cobalt-60 (30 GBq). ཛྷ ཛྷ Soil density and humidity measurement (gammadensimetry), particularly in agriculture and public works. These devices operate with a pair of americium-beryllium sources and a caesium-137 source. ཛྷ ཛྷ Diagraphy (logging), which enables the geological properties of the subsoil to be examined by inserting a measurement probe containing a source of cobalt-60, caesium-137, americium-241 or californium-252. Some sources used are high-activity sealed sources. OPERATING SCHEMATIC of a gamma ray projector Safe position Open position FUNDAMENTALS Selenium-75 gamma radiography The use of selenium-75 in gamma radiography has been authorised in France since 2006. Implemented in the same devices as those functioning with iridium-192, selenium-75 offers significant radiation protection advantages in gamma radiography. The reason for this is that equivalent dose rates are about 55 millisieverts (mSv) per hour and per TBq one metre from the source, as opposed to 130 mSv/h/TBq for iridium-192. In France, about 17% of the devices are equipped with selenium-75 sources. Although the use of selenium has been increasing constantly since 2014, ASN considers that it is still insufficiently used by the industry professionals. Yet it can be used in place of iridium-192 in numerous industrial fields, especially the petrochemical or boilermaking industry, and it enables the safety perimeters to be significantly reduced and facilitates intervention in the event of an incident (see point 5). Shielding Source Plug in safe position Direction of source projection Plug in open position Guide tube