Whilst experts may be forgiven failure to comprehend the fears and limitations of ordinary people, journalists should do better.

It is usual in popular articles on radiation to see statements such as:

uranium fuel was superheated to 3000 degrees,

the accident released a hundred times as much radioactivity as did Hiroshima,

at a hot-spot in the forest, radiation still measured 100 microsieverts,

in some areas of the reactor building, levels were 10,000 Roentgens per hour. To approach meant certain death,

milk contained 20 times the safe level of radioactive iodine,

all of the sheep have been condemned as unsafe to eat. Caesium levels may remain elevated for decades.

Even within the context of the articles from which they were abstracted, the statements are largely meaningless, except to an expert.

This situation, well described as encouraged ignorance, has arisen partly because so many different units are used, but also as a consequence of a desire to maintain mystique.

In the period following the accident at Chernobyl, white coated scientists could be seen engaged in various photo opportunities on windswept hillsides in the UK. Sheep were shown on television being tested (and using equipment that was incomprehensible to the layman), milk was condemned, and advice issued on the safety of eating vegetables.

In reality, everyone involved had a splendid time and no-one was ever at any remotely serious risk from eating or drinking any foodstuff produced in the UK.

Privately, radon experts admitted that had they been offered a few lamb chops from Cumbria or North Wales, or indeed a whole lamb for the home freezer, they would have accepted.

There is a serious point here. In very little of the reporting was any attempt made to set risks properly in perspective and using a single set of units referenced to some 'normal' annual dose. Most of the reporting was based on material from the Departments of Government, and was in terms either of rads, Bq/litre of iodine in milk or Bq/kg of caesium in lamb chops.

It was never properly explained at the time, although it has appeared in various discreet (and discrete) publications since that the doses to members of the public were never remotely dangerous, and certainly not on the scale of a fortnight in some Cornish guest-houses breathing radon.

So what is to be done?

The answer is simple. So simple in fact that a more sinister question needs to be asked: why have journalists for so long accepted and faithfully reproduced what they were told?

There is a concept called effective dose equivalent. It has its faults, but it is simple enough both to understand and to explain on television. Various units can be used, but one, the mSv (see Sections 6 and 7) is recommended.

Effective dose equivalent is simply a calculated quantity that expresses how much harm a given amount of radiation may do, but there is no need even to understand a mSv. It can be thought of as just a very small amount of potential harm. Indeed it has been referred to as a 'basic background unit' of radiation.

In most parts of the UK, people receive between 2 and 3 mSv of dose each year, mainly from natural sources of radiation.

In the USA the average is nearer 4 or 5 mSv, and in Cornwall about 10 mSv.

It is clear that a few mSv cannot be much to worry about: people live in Cornwall quite happily and there are no plans to evacuate them.

What then would be the extra annual dose of eating one Chernobyl lamb from the Cumbrian or Welsh hills? What would be the extra risk from drinking every day for a month, a litre of milk containing 200 Bq/l of radioactive iodine?

Would this be 0.01 mSv, or 0.1 mSv, 10 mSv or perhaps 100 mSv? The fact that most readers will have no idea of the answer (and even less idea how to calculate it) illustrates the point perfectly.

In all future public pronouncements on risk from radiation, whether from a aeroplane flight to Spain, a week camping on a particularly radioactive spot in Cornwall or eating three chops from a Chernobyl lamb, the same quantity and units should be used:

effective dose equivalent and expressed in mSv over the next year.

Only then will the public be able to gain a proper perspective. If the answer (as in the case of Chernobyl in the UK) was less than 0.5 mSv (or even 50 mSv) a shrug of the shoulders would have been an adequate response, albeit recognising the dire needs of those closer to the disaster. Variations in natural background over a lifetime can easily exceed 400 mSv depending upon where people live. This is no cause for great concern.

On the other hand, if the anticipated dose from an accident was 1000 mSv per person, prompt precautions (but not panic) would be sensible.

There is one further and related problem. In the Chernobyl accident about 30 people were exposed to massive doses of radiation and died within days or weeks. Latest estimates of deaths amongst those directly involved in the cleanup range from 250 (apparently the official figure) to 5000. These people received only a small fraction of the total radioactivity that was released. Some was spread over a wide area as moderate contamination, (the exclusion zone has a radius of 30 km) and yet more over a vastly larger area but very much diluted.

Perhaps half of the total radiation dose to humans was received by tens of millions of people at such a low level that it becomes questionable whether it should count at all when assessing the merits or problems of nuclear power.

It is iconoclastic to suggest that an occasional release of radioactivity might be an acceptable and small price to pay for energy, so long as large exposures to workers or other individuals could be avoided.

From Chernobyl, most people in the UK received less than 0.04 mSv, broadly equivalent to spending 20 minutes in some Cornish cellars (where the author has spent hours), flying across the Atlantic, or smoking one cigarette.

This was not how most people perceived the consequences, terrible as the accident was (and still is) for those directly involved.

A recent Editorial in the medical press summarized fear of dilute radiation:

"There are other reasons why some experts may wish to emphasize risk rather than safety. In every country some may have political or fund-raising reasons for their choice of words. Or perhaps, like the media, they want to feel on the same side as those who are alarmed - rather than be accused of being patronizing or unsympathetic".

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