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How much radiation are you exposed to per year?

If you’re scared of radiation exposure, you could do well to stay away from humans, granite and bananas. They’re the new silent enemies.

To be fair they won’t kill you, but you may be surprised how much radiation they emit.

Radiation is a scary thing, and everyone is wary of being exposed – whether it be from nuclear power plants or mobile phones. But which sources of radiation are actually the most dangerous? And how much exposure can be life-threatening?

In most cases, radiation exposure poses no threat to human life. According to Australian scientist Dr Karl Kruszelnicki, everyone is covered in an invisible ocean of radioactive particles and energies, arriving through alpha and beta particles, gamma rays and X-rays.

There are different methods of measuring radiation exposure, Dr Karl talks in terms of REM (Roentgen equivalent in man). But there is also the Sievert (Sv), or milli-Sievert (mSv).

To put things into perspective, one REM will give you about a 1 in 2000 chance of developing cancer. So that is 0.01 Sv, or 10 mSv. The natural radiation humans are exposed to is 2 mSv per year, while Dr Karl said the average for Americans in total is 3.6 mSv per year.

The Guardian reports that a single dose of 10,000 mSv will kill you in weeks, while a typical dosage of 6000 mSv was recorded in Chernobyl workers who died within months.

A CT scan of your heart? 16 mSv. CT scan of the head? 2 mSv. A chest x-ray? 0.1 mSv (though Dr Karl and other sources suggest it is 0.36 mSv).

And for those concerned about the after-effects of the Fukushima disaster, 1.02 mSv was detected per hour.

Granite, which usually carries tiny amounts of uranium, can let off 200 millirems (two mSv), so if you’re paranoid, avoid granite kitchen benches.

Radioactive decay from skin gives us 40 millirem per year (0.4 mSv), while clothes, paper, concrete and food are slightly radioactive.

Those living at higher altitudes are also exposed more, due to cosmic rays which clash into nitrogen and oxygen atoms and penetrate towards the ground. Dr Karl says that living at 3000 metres will add 1 mSv.

He also says that nuclear bombs of the past are believed to give Americans an extra 1 millirem per year (0.01 mSv), plus another from nuclear power plants. Meanwhile, 10 millirem (0.1 mSv) come from battery-powered smoke detectors.

As for that banana? Fear not, it only accounts for 0.0001 mSv (or 0.01 REM), so we were fibbing when we said it was the enemy. Eat them, they are delicious, and good for hangovers.

But seriously, avoid cigarettes (if you weren’t already aware), and probably not avoid getting relocated to Chernobyl.

There is no way of escaping radiation, because many objects are constantly emitting radioactivity. The key, of course, is to avoid high levels. It also depends on which part of your body is exposed – your bone marrow is more sensitive than your big toe, for example.

Dr Karl uses the handy analogy of a boxing bout – if you receive 50 little punches to your left leg, you’re going to be okay. Yet if those punches, with the same ferocity, were directed towards your left eyeball, it’s going to be a bad time.

So do not X-ray your eyeball.

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