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A pair of research chambers in Ottawa are used to measure minute amounts of radioactivity in the body.
We may not realize it, but we are all radioactive. “We’re submerged in radiation,” says Dr. Gary H. Kramer of Health Canada. “It comes from the environment, from around us, from within us. It’s coming from almost everything.”
Measuring the radioactivity in the body is an important first step in assessing the health risk from internal contamination, which happens when someone accidentally ingests or inhales radioactive material.
This is particularly important for people who work with radioactive sources, such as hospital workers, scientists, and staff at nuclear power plants. In Ottawa, Ontario, the National Calibration Reference Centre for Bioassay and In Vivo Monitoring houses two chambers that can detect minute amounts of radioactivity in the body. The chambers are mainly used to check the accuracy of test samples that in turn are used to test the accuracy of radiation detectors in nuclear power plants and other Canadian facilities. This has a direct impact on the safety of employees, making sure that the calculation of an individual’s radiation dose is as accurate as possible.
The chambers are also used for research and development, and sometimes after an accident, such as the time that a worker who wasn’t wearing protective gear got a facefull of uranium ore dust. “He had a uranium lung burden just below the dose limit — he was OK,” says Dr. Kramer. The chambers’ walls are thick to reduce background radiation, which comes from everywhere, including people, buildings, radioactive sources in the Earth and cosmic rays from outer space.
The walls of the lung counter consist of four layers of shielding: steel, lead, tin and lastly copper. “Lead is a great choice because it’s so dense,” says Dr. Kramer. “You don’t need much of it.” Each layer progressively reduces the amount of external radiation that penetrates the walls, so that the highly sensitive detectors mainly pick up radiation in the person being scanned. Dr. Kramer points out that while shielding reduces the amount of radiation inside the chambers, it can never be eliminated entirely.
“There are trace levels of radioactive cesium in the steel of the whole body counter, left over from the bomb tests in the 1960s,” he says. “At that time, we were all walking around with small amounts of radioactive cesium in us.”
ISSN 1927-0275 = Dimensions (Ottawa. Online)