The Journey of a Dosimeter: Tracking Workers’ Exposure to Ionizing Radiation

July 6, 2023


What do dental offices, vet clinics, hospitals, and mines have in common? All of them, plus many other industries, use radiation as an important tool in their day-to-day operations. This can present a health risk to workers if their exposure to ionizing radiation is not properly monitored and controlled. Rest assured that measures are in place to protect these workers while on the job!

Measuring Radiation

Radiation dosimetry is the science of measuring exposure to ionizing radiation. Unlike other types of radiation, ionizing radiation has enough energy to remove electrons from atoms and molecules, which can cause damage to human cells. The amount of radiation a worker is exposed to is called a dose.

In industries that use radiation as part of their operations, it is the employer’s responsibility to protect the health and safety of their workers. Radiation dose can be measured using a dosimeter, which is a small device worn either on the front of the body or on an extremity, such as a wrist or finger. The employer provides the workers with dosimeters, keeps track of their radiation dose, and ensures it stays within safe limits.

Since 1951, Health Canada has been supporting occupational dose monitoring through its National Dosimetry Services (NDS). NDS has nearly 13,000 client organizations, adding up to over 100,000 Canadian workers that need dosimetry services.

The life cycle of a dosimeter

Giving it wings

Each worker needs several dosimeters over the course of one year. Dosimeters are shipped out to workers at the beginning of each “Wearing period”, which is usually every 3 months, or shorter for high-risk occupations. This means Health Canada prepares, ships, receives, and analyzes over 600,000 dosimeters a year! The workhorses of the Department’s NDS Operations Section are three custom-built machines that assemble and label the dosimeters before they are shipped out to clients. These machines can assemble 750 dosimeters in an hour!

“The machines have to be fine-tuned so that everything aligns within less than a millimetre, the barcodes on each dosimeter have to be read and linked to the worker information in the database… there are a lot of complex interactions that go into assembling the dosimeters”, says Elizabeth Inrig, Manager of Health Canada’s Dosimetry Sciences and Support Section. Once the dosimeters are assembled, another team ships them out to clients.

Video transcript

0:00-0:02 Individual disassembled black dosimeter slides fall into large rotating circular drum that is collecting dosimeters in a single file line.

0:02-0:06 Inside the machine, the robot arms assemble the dosimeters.

0:06-0:12 Machine picks up disassembled dosimeter slides one at a time and places them onto a conveyor belt which rotates and inserts each dosimeter into another machine with a slot.

0:12-0:17 A wide view of both machines. On the right, the assembled dosimeters are falling into the large rotating circular drum that is collecting assembled dosimeters in a single file line. Towards the top left, the assembled dosimeters are picked up by machine one at a time and placed onto a conveyor belt.

0:17-0:30 The machine picks up each dosimeter one at a time and disassembles the slide from the blue case. The robotic arm removed the blue plastic case and drops it into a slot. The machine places the black disassembled dosimeter slide in the automatic reader.

Coming back home

At the end of the wearing period, the dosimeters are returned to Health Canada. The same machines that assemble the dosimeters can rapidly be switched to another mode which disassembles them. The disassembled dosimeters are loaded into the automated readers and analyzed.

The dosimeters used by NDS are based on a technology called Optically Stimulated Luminescence (OSL), which converts stored energy from radiation into a blue light signal that is easy to measure.

Technologists then review the data and determine how much of the dose came from naturally-occurring radiation in the environment and how much was due to radiation exposure in the workplace. It’s this “occupational dose” that is reported to the National Dose Registry (NDR), which tracks a worker’s dose over their lifetime – even as they move between jobs.

Reduce, Reuse, Recycle

Once the dosimeters have been analyzed and each worker’s dose has been reported, they are reset and loaded back into the machines, where their life cycle begins again. Fortunately, everything can be reused, so it’s a very efficient process.

The mighty power of dosimetry

Dosimetry plays an important role in identifying and managing risks linked to ionizing radiation. In addition to monitoring workers’ daily exposure, dosimetry would play a critical role in the unlikely occurrence of a radiological or nuclear emergency, where first responders and others could be at risk of exposure. Dosimeters can also be used for research, and Health Canada also uses them to measure background dose rates across Canada. If you would like to find out more about the NDS and the health effects of radiation, please refer to the resources below.

Additional Resources