By Michelle Roberts
BBC News Online health staff
It is widely accepted that high doses of radiation are harmful and can cause cancers like leukaemia.
Scientists disagree about what levels are damaging
The aftermath of atomic bomb explosions and fallout from nuclear weapons tests and radiation accidents are proof of this.
But some experts believe a little radiation may actually be good for you.
They say low-dose exposure to radiation, such as through x-rays and other medical scans, could have a positive effect on the body, in addition to diagnosing diseases.
But others, including experts who advise the government on radiation levels, say any exposure could increase the chance of cancer.
Dr Paul Dubbins from the Royal College of Radiologists explained: "The scientific community sits on exactly opposite sides of the divide.
"And both groups have scientific evidence and reports to support their position so it depends on which side of the scientific divide you sit."
So who should you believe?
Dr Dubbins said: "In this country, what we have done is use the data predominantly derived from Hiroshima and the incidence of cancers and leukaemias from people exposed to radiation during Hiroshima.
"If you extrapolate that information backwards you assume that there is a linear response with no threshold - that any dose of radiation is theoretically bad for you unless it can be balanced against the benefits that you will get from a diagnosis.
"So we will use radiation only if it is justified by the clinical symptoms and clinical presentation.
"Because of that approach, to reducing the impact of radiation, this country has had the lowest rate of radiation-induced cancer.
"So in a sense, you takes your pick and you has your choice.
What are the risks?
Researchers, who published their work in The Lancet medical journal in January, calculated that the additional radiation exposure from medical X-ray tests would increase a UK person's cumulative risk of developing cancer by the age of 75 by 0.6%.
This is equivalent to around 700 of the 124,000 new cases of cancer diagnosed in the UK every year.
Dr Michael Clarke from the National Radiological Protection Board, which advises the government about safe radiation levels, said: "We know radiation damages a cell's DNA.
It is the energy produced from natural and man-made radioactive materials
It is present in the environment because of naturally occurring radioactive minerals
Man-made sources include medical treatments and diagnostic aids, industry and fallout from previous nuclear weapon explosions and other accidents/incidents world-wide.
Source: National Radiological Protection Board
"The problem is that, with low doses, it is difficult to do any experiments on animals or humans so we are basing things on our assumptions.
"The most sensible scientific judgement you can make is that any level is harmful because that mechanism of damage to DNA will happen even if only one cell is hit.
"We think that's not a particularly good thing. But of course it is a tiny risk."
Professor Zbigniew Jaworowski, former chairman of a United Nations committee on radiation effects, disagrees.
He said a study in the Iranian city of Ramsar had shown people routinely exposed to 250mSv - which was much higher than the 70mSv recommended as a safe background level of exposure in the UK at the time - came to no harm.
"There were many generations of people living in these houses, and there was no evidence of any harm. One of the gentlemen living there was more than 100 years old."
Professor Jaworoski said the view that low levels of radiation were harmful was little more than an "administrative assumption".
Professor John Cameron, professor emeritus from the University of Wisconsin-Madison, believes low levels may actually be beneficial to a person's health, boosting the body's immune system which fights off infections.
"It's been known for some time that radiation stimulates the immune system.
"Studies show animals live longer with an increase of radiation.
"I believe a 100-year study of British radiologists is the most important study of health effects of moderate dose rate radiation ever published."
It compared the death rates of British radiologists, who registered with a radiological society between 1897 and 1979, from cancer, non-cancer and all causes to those of all male non-radiologist physicians in England and Wales.
Professor Cameron said: "There was no evidence of an effect of radiation on diseases other than cancer even in the earliest radiologists, despite the fact that doses of the size received by them have been associated with more than a doubling in the death rate among the survivors of the Japanese atomic bombings.
"There's no doubt in my mind that radiation at moderate levels is beneficial.
"The trouble is none of these studies prove scientifically that it is the case because we would need to do a randomised controlled study - expose some people to radiation and others not."
He said this would be hard to do in practice because of the ethical problems it would pose.
"So the evidence is anecdotal, but it's strong," he said.
Professor Adrian Dixon, clinical director of Radiology at Addenbrooke's Hospital in Cambridge, disagrees.
"There's a bit of very tenuous research which doesn't really outweigh the potential catastrophe.
"It's curious that these is not a greater variation of cancer in places with high background radiation.
"But equally, they do not do any better so that doesn't suggest that low dose is good for you either.
"I do not think we will ever be closer to knowing for sure."