We live on a planet full of natural radiation.
It is present in soil, rocks, the air we breathe, the water we drink, and even in our own bodies.
This natural radiation makes up the bulk of the total radiation we are exposed to every day. But we’re also exposed to artificial radiation,
including medical tests like x-rays, and small amounts of radioactive material
– called “radionuclides” – from licensed releases
from nuclear facilities. I’m Julie and I work for
the Canadian Nuclear Safety Commission. We can’t see, hear, smell, touch or taste
radiation. Until 1895 we didn’t even know it existed!
But we’ve come a long way in our understanding about what ionizing radiation is
and how it affects our bodies and our environment. For example, we can measure the amount of
radiation in the environment with radiation detection
devices – like Geiger counters.
They count the energy deposited in the detector by the radiation.
Listen to the sound of naturally occurring uranium
in this rock sample. [clicking sound intensifies]
That count can then be used to calculate a dose. A dose is the quantity we use when we talk about the potential health effects of radiation. A dose takes into account the type of radiation
you’ve been exposed to and the organs in your body
which have been exposed. It is expressed using the unit “sievert”
or more commonly “millisievert” which is 1,000 times smaller. On average, Canadians receive a dose of 1.8 mSv every year from natural background radiation coming from radioactive materials found in soil, rocks,
some foods and cosmic radiation. This number can range from 1 to 4 mSv
depending on where you live in Canada. For example, the cosmic radiation is more
intense for people living at higher altitudes
or further from the equator. Likewise, terrestrial radiation is higher
for people living in areas where rocks and soil contain
more natural radioactive elements. So what are the health effects caused by radiation?
Certain types of radiation have enough energy to penetrate our bodies.
When it passes through tissues in the body, electrically charged atoms, called ions,
can change or destroy cells. The body is a pretty amazing organism and
most of the time, these cells repair themselves.
This can happen millions of times every day! If however the DNA or other critical parts
of the cell receive a large dose of radiation all at once,
the cell may die or be damaged beyond repair. If this happens to a large number of cells,
“tissue effects” can occur. Examples of these effects include cataracts,
which can happen at around 500 mSv, and acute radiation syndrome symptoms like
nausea and skin burns that can be seen at doses well
over 1,000 mSv. Extremely high levels of radiation in the
range of 4,000 to 5,000 mSv can be fatal.
This level of exposure is very rare. If the cell incorrectly repairs itself, but
continues to live, then “stochastic effects” could occur.
This type of damage could develop into cancer over time.
The higher the radiation dose, the more likely a cancer will occur.
In population studies, we generally don’t observe
health effects appearing at doses lower than about 100 mSv.
Most importantly, our understanding of how cells
can be damaged by radiation allows us to use that same knowledge to target and kill cancer
cells. We know what happens once radiation enters
the body, but how does it get inside you in the first
place? When we talk about radiation exposure,
we are talking about “pathways”; there are various pathways radiation can take
to get inside the body – including the air we breathe
and the food we eat – all of which contribute to our radiation dose.
Did you know a brazil nut naturally contains trace amounts of the radionuclides potassium-40
and radium-226? Delicious! Our bodies can’t distinguish between natural
and artificial radioisotopes. One source of artificial radiation is the
small, controlled quantity of radionuclides permitted
to be released from licensed nuclear facilities into the environment.
These radionuclides could be carried in the air
and deposited in a farmer’s field. Animals eat grass and grains from that field
and then provide food that people eat and drink.
Understanding that chain of events – that one pathway –
makes it possible to begin estimating a dose to the person who consumes that food.
Overall, the amount of radionuclides in foods are extremely small and do not affect your
health. For major facilities, a similar assessment
is done to look at the impact of radiation
on the environment itself, including wildlife and vegetation.
Since radiation has the potential to cause harm,
it must be strictly regulated. That’s where the Canadian Nuclear Safety Commission
comes in; our mandate is to regulate the use of nuclear energy and materials
to protect health, safety, security and the environment.
The Radiation Protection Regulations define the dose limits used to protect
the health of the public and nuclear energy workers.
Members of the public are limited to 1 mSv of exposure
per year from licensed activities; this is in addition to all other sources of
radiation, like naturally-occurring or medically-related
radiation. Workers are limited to 50 mSv in one year
and 100 mSv over 5 years. Nuclear energy workers can wear small devices
called “dosimeters” that measure and track their radiation doses as one way to make sure
they don’t exceed these limits. These can be worn on different parts of the
body depending on the kind of work they do.
It’s important to note that these dose limits are regulatory limits, and not health limits.
As a result of our strict regulations and oversight,
we are happy to report that these dose limits are rarely reached.
I’ve given you a lot of information. Let’s put some of the numbers in perspective.
Members of the public living near a major facility typically
receive 0.001 mSv a year from licensed nuclear activites,
which is less than a typical chest x-ray (0.1 mSv).
The public dose limit is 1 mSv per year. This is on top of the dose received through
natural background radiation which in Canada is nearly twice that high, at an annual average
of 1.8 mSv. Workers are limited to 50 mSv in one year
or 100 mSv in 5 years. In fact they typically get far smaller doses.
Health effects like cataracts can happen at 500 mSv
and acute radiation syndrome symptoms can be seen at doses well over 1,000 mSv.
I know radiation doses can sound scary, but you can rest assured;
the Canadian Nuclear Safety Commission is there,
overseeing the nuclear sector to protect your health and safety, as well as that of
the environment. The Canadian Nuclear Safety Commission:
the answers you need, from a source you can trust!
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