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Everyday doses

Radiation and the atom · level 6, lesson 3 of 6

A question to start

Everyone on Earth gets some radiation every day, from rocks, the air, food and space. How big is it, next to an X-ray or a flight?

The idea

The Canadian Nuclear Safety Commission gives these typical doses:

Dose mSv
Dental X-ray 0.005
Flight across Canada 0.02
Chest X-ray 0.1
Limit for the public each year, from nuclear industry 1
Natural radiation in a year, Canadian average 1.8
Natural radiation in a year, world average 2.4
Chest CT scan 7
Limit for nuclear energy workers each year 50
A year on the International Space Station, average 150
A dose that may cause radiation sickness about 1,000

The natural dose changes from place to place. Of Canada's 1.8 mSv a year, about half (0.9) comes from breathing radon. It is 1.3 mSv a year in Vancouver, 1.6 in Toronto, 2.5 in Halifax and 4.1 in Winnipeg, mostly because of the radon from different ground.

0.0010.010.11101001,000 dental X-rayflight across Canadachest X-raya year of natural radiation in Canadachest CTworker limit for a yeara year on the space stationradiation sickness

Each step up the scale is ten times the one below. The numbers are in mSv.

Worked examples

1. X-rays and a year. A year of natural radiation in Canada is \(1.8 \div 0.1 = 18\) chest X-rays.

2. A CT scan. \(7 \div 1.8 \approx 4\): one chest CT is about four years of natural radiation.

3. Space. A year on the space station is \(150 \div 1.8 \approx 83\) years of Canadian natural radiation.

Try it

  1. Which gives a bigger dose: a flight across Canada or a dental X-ray? By how many times?
  2. How many chest X-rays add up to the worker limit for a year?
  3. Where does half of Canada's natural dose come from?
  4. Why is the natural dose higher in Winnipeg than in Vancouver?
Answers
  1. The flight: \(0.02 \div 0.005 = 4\) times.
  2. \(50 \div 0.1 = 500\).
  3. Breathing radon.
  4. More radon comes up from the ground there.

Common mistake

"Any radiation is dangerous." Everyone gets natural radiation all their lives. What matters is how big the dose is. The limits are set far below the doses known to cause harm.

Where it leads