We are all exposed to some radiation throughout the year. Radiation is energy travelling through space and sunshine is one of the most familiar forms. It delivers light, heat and suntans and we limit its effect on us with sunglasses, hats, clothes, sunscreen, shade and by staying indoors.
We are also exposed to higher energy kinds of radiation which are used in medicine and which we all get in low doses from space, from the air, and from the earth and rocks. Collectively these kinds of radiation are called ionising radiation.
However, when the exposure level becomes too high, it can be very damaging to our health.
It has been known for years that large doses of ionising radiation, very much larger than background levels, can cause a measurable increase in cancers. Leukaemia, a bone marrow cancer, is the most common radiation-induced cancer. According to experts even radiation doses as low as 100 mSv can slightly raise cancer risk, whereas exposure to 1 000 mSv may increase the risk of fatal cancer by 5%.
Exposure to very high levels (10 000 mSv) can cause sickness and death within weeks, whereas 50% of people exposed to a dose of between 4 000 and 5 000 mSv will die within a month.
Symptoms of acute radiation (exposure within one day):
- 0–250mSv: none
- 250 to 1 000 mSv: some people feel nausea and loss of appetite; bone marrow, lymph nodes, spleen damaged. (250mSv to 1000mSv)
- 1 000– 3 000 mSv: mild to severe nausea, loss of appetite, infection; more severe bone marrow, lymph node, spleen damage; recovery probable, not assured.
- 3 000 mSv –6 000 mSv: severe nausea, loss of appetite; haemorrhaging, infection, diarrhoea, skin peels, sterility; death if untreated.
- 6 000 mSv – 10 000 mSv: above symptoms plus central nervous system impairment; death expected.
- Above 10 000 mSv: incapacitation and death.
Here's a summary of radiation exposure at different levels:
(radiation reading in millisievert - mSv)
- Living near a nuclear power station: less than 0.01 mSv/year
- Dental X-ray: 0.01 mSv
- Chest X-ray: 0.10 mSv
- Mammogram breast X-ray: 0.40
- Typical natural background radiation for all humans: 2 mSv/year
- Head CT scan: 2 mSv
- Average dose to US nuclear industry employees. 2.4 mSv/year
- New York-Tokyo flights for airline crew: 9 mSv/year
- Full-body CT scan: 10 mSv
- Smoking 1.5 packs/day: 13 mSv/year
- Heart CT scan: 16 mSv
- Current average limit for nuclear workers: 20 mSv/year
- Lowest annual dose at which any increase in cancer is clearly evident: 100 mSv/year
- Criterion of residents who were relocated after Chernobyl disaster: 350 mSv/lifetime
- Likely to cause fatal cancer some years later in 5% of people exposed: 1 000 mSv/cumulative
- Causes radiation sickness: 1 000 mSv single dose
- Would kill 50% of people within a month of exposure: 5000 mSv single dose
- Dosage recorded in those Chernobyl workers who died within a month: 6 000 mSv
- Fatal within a few weeks: 10 000 mSv single dose