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natural radionuclides are present in the sea and these are transferred to fish and
shellfish.
On average, a person receives 235 μSv every year from natural radioactivity in
food. Approximately 75 percent of this is due to potassium-40. Potassium is an

essential element and its concentration in the body is controlled by metabolic
processes.

 Exposure to artificial radiation

The principal sources of man-made or artificial radiation are as follows

1) Medical exposure of patients

Many procedures carried out routinely in medical diagnosis involve exposure
to radiation. On average, a person receives 540 μSv per year from medical
procedures. This average value does not include doses from medical treatment such
as radiotherapy, which will normally be several hundred times higher.

Some people receive no dose from medical procedures while others receive
much higher doses. The total dose received depends on the number and type of
procedures.
Some well-known procedures and the typical doses received are:
dental X-ray (10 μSv);
chest X-ray (20 μSv);
mammography to identify breast cancer (500 μSv);
CT scan (5400 μSv);
angiocardiogram to determine heart function (6000 μSv).

All medical exposures to radiation must be clinically justified and should only be carried
out if recommended by a GP or medical consultant. Exposure to radiation as part of a routine
medical check-up is rarely if ever justified.

2) Working with radiation

If you work with radiation in the medical, industrial or education/research
fields, on average you receive a dose of 20 μSv per year.

Air crew who fly above 8000 m receive an average dose each year of 2000
μSv. As mentioned above, the average contribution from radon in indoor workplaces
is 180 μSv. If you work with radiation or are air crew, your employer is required by
law to keep a record of your doses. The radiation exposure is carefully monitored
with the use of pocket-pen-sized instruments called dosimeters.

Stringent rules and regulations are in place to protect workers from accidental
exposure to harmful levels of radiation.

Examples of industries where occupational exposure is a concern include:

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