Killer that could not be put back in the test tube

It was 100 years ago this month that Henri Becquerel discovered radioactivity. Geoffrey Lean on the demon that has always been with us

A HUNDRED years ago this month, Henri Becquerel opened a drawer on to the atomic age. And it was all an accident.

A few days earlier, the middle-aged French scientist had put some photographic plates away in the drawer, weighting them with bits of a mineral containing uranium. When he developed the plates he found, to his surprise, that they had darkened, even though they had been kept away from the light. He deduced that they had been affected by radiation, which he traced to the uranium.

Moving with a speed far surpassing our computer-powered age, Becquerel announced his discovery of radioactivity the next evening at a meeting of the French Academy of Sciences, and published a paper 10 days later. (Nowadays the process would have taken months, while a scientific journal meticulously checked and refereed his paper before venturing to print it.)

He was followed up by a young Polish-born chemist who was looking for a subject for her doctoral thesis: Marie Curie. She and her husband, Pierre, discovered that, as uranium gave off radiation it mysteriously changed into other elements - one of which they called polonium after her homeland, and the other, radium, the "shining" element. In 1903 Becquerel and the Curies shared the Nobel prize for physics.

They soon discovered, at first hand, the effects of radiation on life. Becquerel borrowed a vial of radium from Marie Curie and put it in his pocket, only for it to burn his skin through several layers of clothes. Marie Curie paid a higher price, dying of leukaemia (the Curies' notebooks are still dangerously radioactive).

In all, at least 336 early radiation workers died from their exposure. The first, rough and ready, exposure limits were not set until 1934.

Becquerel's finding may eventually have led to nuclear power and the atomic bomb, but he only discovered radioactivity in the sense that Columbus (or, rather, Erikkson) discovered America. It had always been there. It took part in the Big Bang, pervaded the cosmos and became inextricably bound to Earth from its formation. Even human beings are slightly "hot", for all living tissues naturally contain traces of radioactive substances.

Even today, despite environmentalists' campaigns against nuclear energy, we get almost all our exposure to radiation from natural sources. Britons, as a whole, receive 8,500 times as much radiation from nature as from nuclear power.

Part of this comes from cosmic rays from deep in space. These increase with altitude. Levels are more than 150 times greater at 12,000 metres, where the highest inter-continental flights cruise, than at sea level. A single transatlantic flight exposes the average Briton to more than 100 times as much radiation as he or she receives from discharges from nuclear power stations in a year. More comes from the ground or naturally occurs in food.

About half of the average Briton's total exposure is from radon, an invisible, odourless gas which seeps out of the earth and gets trapped in houses. The National Radiological Protection Board estimates that 250,000 Britons - including vulnerable children and pregnant women - are irradiated with double the average dose received by workers in the nuclear industry; 100,000 homes are badly affected - 60,000 in Devon and Cornwall, the rest scattered about the country. Radon is the second greatest cause of lung cancer in Britain, after smoking.

Only about 15 per cent of the average radiation dose comes from man-made sources - and 93 per cent of that is from medical x-rays. Much of this is unnecessary: exposures can vary up to 10-fold for the same x-ray from hospital to hospital.

Of course, people living near atomic plants, such as Sellafield, receive a much higher dose from nuclear power than the average, and there is the ever-present fear that a nuclear accident could release vast amounts of radiation.

But those concerned about radiation exposure might be better occupied pressing for counter measures against radon in houses, neglected by the Government, or for reducing over-expo- sure to x-rays, rather than campaigning against routine emissions from nuclear power stations.