Calculating Exposure

Ionizing radiation can be in the form of alpha particles, beta particles, neutrons, gamma rays and x-rays. Each type has different damaging qualities when absorbed by a living organism. In Canada, the sievert (Sv) is used to measure ionizing radiation exposure. The sievert measures the overall damage to a living organism regardless of the type of ionizing radiation. The scientific definition of a sievert is one joule (J) of energy deposited in one kilogram of mass, multiplied by a “weighting factor” that takes into account the different biological effects of the various form for radiation (alpha, beta, gamma, neutrons, or X-rays). A joule is the amount of energy required to move one kilogram of mass a distance of one metre. The average Canadian will receive approximately 0.0027 sieverts or 2.7 millisieverts (mSv) of ionizing radiation from all sources, both natural and man-made, in one year.

You may ask yourself “Is that amount safe?” The answer is yes. Exposure to ionizing radiation of 5 sieverts over a short period of time would prove fatal to a significant portion of the population. The average person receives less than three one thousandth’s of one sievert each year. Scientists traditionally have assumed the effects of radiation exposure to be cumulative, meaning that its effect builds up over time. For that reason, a yearly limit is set by government agencies. The Canadian Nuclear Safety Commission (CNSC) sets the maximum limit at 50 millisieverts for people working in the nuclear industry.

nuclear worker
Nuclear workers do not experience higher rates of cancer or other illness than members of the public.

People who work in Canada’s nuclear industry are allowed to receive more than 10 times the amount of ionizing radiation per year as you, a member of the general public, are allowed to receive. Most nuclear workers receive a small fraction of the limit. After 50 years of monitoring and studying people employed in the nuclear industry, it has been determined that they do not experience any higher rates of cancer or other illness than people in the general public. This is to be expected, since the doses are well below those known to cause negative health effects. In fact, the people employed in the nuclear industry seem to be healthier and have less incidence of cancer than the general public.

Radiation Doses and Effects
Millisieverts
Effect
10,000
Fatal within weeks
6,000
Typical dosage recorded in those Chernobyl workers who died within a month
5,000
Single dose which would kill half of those exposed to it within a month
1,000
Single dose which would cause radiation sickness, nausea, but not death
400
Maximum radiation levels recorded at the Fukushima plant on March 14, per hour
350
Exposure of Chernobyl residents who were relocated
100
Lowest level linked to increased cancer risk
10
Full-body CT scan
9
Exposure of airline crew travelling the polar route from NYC to Tokyo, per year
2.4
Natural radiation to which we are all exposed, per year
0.1
Chest x-ray
0.01
Dental x-ray