Introduction

Radiation is a natural phenomenon.

The current method of measuring absorbed radiation is the effective dose equivalent in units called millisieverts, mSv. This allows different types of radiation from different sources, X-rays, gamma rays, cosmic rays, etc. to be compared. Normal exposure in London is about 0.18 mSv per month including that from cosmic rays and natural radioactive potassium and radon in our bodies. The computed risk of death from 0.1 mSv is one in a million, which is the same risk as smoking one and a half cigarettes in a lifetime or drinking half a litre of wine in a lifetime or, indeed, the risk of death for a man aged 42 living for a day or a man aged 60 living 20 minutes.

Perception of risk

The popular perception of radiation risk is much greater than in fact it is. Studies in the USA of League of Women Voters and college students put the risk of nuclear power first and business and professional club members put the risk at eighth of a list of 30 agents, whereas in fact it was 20th (the risk was 1500 times less than average cigarette smoking, 1000 times less than average alcohol consumption, 500 times less than motor vehicle driving, 30 times less than swimming and 10 times less than bicycling). The lifespan shortening on a population basis associated with medical X-ray is 6 days, of which the nuclear medicine contribution is 4 hours as compared with natural background radiation 8 days; accidents in the home 95 days; accidents at work 74 days; and heart disease 2100 days as examples.