Just The Right Amount: Using Dosimetry to Measure Absorbed Radiation

25 April 2013
Ionizing radiation is used in agriculture - to prevent sprouting or ripening, to eliminate pathogens that can cause sickness in humans, and to kill insects that can disrupt the ecosystems of importing countries. <br /><br />(Photo: T. Kalapurackal)Ionizing radiation also slows decay in certain foods, especially packaged goods. These two jars contain identical quantities of cowpeas that had been stored for 15 years when this photo was taken. The unirradiated cowpeas have almost completely decayed. <br /><br />(Photo: S. Henriques/IAEA)In the same way that bacteria only die after boiling in water for 5 minutes or more, the irradiation process is only effective if the materials are exposed to the right amount of radiation. Too little, and the radiation treatment is ineffective.<br /><br />  (Photo: UNIDO/IAEA)The amount of radiation energy absorbed is measured in kilograys (kGy). Dosimetry is the measurement of absorbed doses. Here, dosimeters used during the irradiation of a package of shrimp are labelled with product, dose absorbed (8kGy), and date of procedure. <br /><br />(Photo: S. Henriques/IAEA)To measure an absorbed dose, technicians like Jonathan Okai Armah at Ghana's Radiation Technology Centre, use... <br /><br />(Photo: S. Henriques/IAEA)Liquid dosimeters (in glass ampules)... <br /><br />(Photo: S. Henriques/IAEA)And solid dosimeters (dye-filled Perspex). <br /><br />(Photo: S. Henriques/IAEA)'Go/no go indicators' like these, which are dye-infused stickers made of Perspex, don't measure absorbed dose, they simply indicate that products have been irradiated by changing colour. <br /><br />(Photo: S. Henriques/IAEA)Dosimeters, which are included with items that are about to be irradiated, are devices that can absorb radiation, undergo a change as a result, and be tested to reveal exactly how much radiation a product has absorbed. <br /><br />(Photo: S. Henriques/IAEA)At Ghana's Radiation Technology Centre, products to be irradiated are placed in these metal bins that run on tracks into the irradiation chamber...<br /><br /> (Photo: S. Henriques/IAEA)... and then back out again.<br /><br /> (Photo: S. Henriques/IAEA)Products that go through the irradiation process do not become radioactive themselves. And neither do the dosimeters that measure dose.<br /><br /> (Photo: S. Henriques/IAEA)Dosimeters change colour, conductivity or composition. How much change depends on how much radiation is absorbed.<br /><br /> (Photo: S. Henriques/IAEA)The IAEA has helped train dosimetry technologists for more than 30 years. In the last decade the Agency has trained hundreds of technologists from around the world.<br /><br /> (Photo: D. Calma/IAEA)Most of these photos were taken at the Radiation Technology Centre (RTC), which is owned by the Ghana Atomic Energy Commission. The IAEA helped Ghana set up the facility in 1994. With further investment from the Ghanaian government, operations have expanded over the years, and the RTC now irradiates about 30 000 kg of products each year. As well as being a commercial enterprise, the RTC also undertakes research.<br /><br /> The fruit, Atitↄ, pictured here, can be eaten raw or used to make alcoholic and non-alcoholic drinks. <br /><br />(Photo: S. Henriques/IAEA)
Last update: 15 October 2014