Polonium-210 is a naturally occurring radioactive material that emits highly hazardous alpha (positively charged) particles.
It was first discovered by Marie Curie at the end of the 19th century.
There are very small amounts of polonium-210 in the soil and in the atmosphere, and everyone has a small amount of it in their body.
At high doses, the substance damages tissues and organs.
Polonium-210, historically called radium F, is very hard for doctors to identify.
Yasser Arafat may have been poisoned with polonium-210
It cannot pass through the skin, and must be ingested or inhaled into the body to cause damage.
And because the radiation has a very short range, polonium-210 only harms nearby tissue.
The substance has industrial uses such as static control and as a heat source for satellite power supplies, but is not available in these areas in a form conducive to easy poisoning.
Polonium-210 is also present in tobacco.
Although polonium-210 occurs naturally in the environment, acquiring enough of it to kill would require individuals with expertise and connections.
Polonium-210 would also need sophisticated lab facilities – and access to a nuclear reactor.
Alternatively, it could have been obtained from a commercial supplier.
Polonium-210 can either be extracted from rocks containing radioactive uranium or separated chemically from the substance radium-226.
Production of polonium from radium-226 would need sophisticated lab facilities because the latter substance produces dangerous levels of penetrating radiation.
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A new radioactive cream can obliterate tumours caused by the most common skin cancers without surgery or conventional radiotherapy in just two hours.
According to Italian scientists, the new technique has minimal side effects and the treatment does not even leave a scar.
The vast majority of those who suffer the less dangerous forms have surgery to remove the affected tissue.
Other treatments include radiotherapy and “freezing” of the tumours if they are small and superficial.
An estimated 3% of patients have deep tumours which are difficult to remove surgically because they are on sensitive areas such as the eyes, nose or ears. Others cannot have surgery due to age or medical conditions.
These patients are given radiotherapy, which involves at least ten sessions at a hospital and often results in serious side-effects.
For the new technique, the researchers harnessed rhenium-188, a radioactive isotope which was previously rare and expensive but is now being supplied in quantities large enough to treat thousands of patients a week by nuclear physicists at the British-funded Institut Laue-Langevin in France.
The treatment, which is said to be painless, involves putting a piece of surgical foil on the tumour area, painting on the radioactive paste and removing it one or two hours later.
Researchers believe that the radiation causes healthy skin to re-grow, so there is no scarring.
In the Italian trial, 85% of patients were cured after one treatment and up to 95% after three treatments.
Oliver Buck, chief executive of the German technology firm ITM which developed the therapy, said: “This means that patients with large and difficult-to-treat tumours not only have hope but keep their quality of life under what would otherwise be dire conditions.
“These people sometimes have to go through horrible surgery which removes part of their face. By contrast this treatment is generally done in a single non-invasive session.”
Trials are now being held in Germany and Australia, and Oliver Buck believes the treatment could be licensed in the UK within two years. He says it will “certainly” be cheaper than current therapies.
Oliver Buck said: “The radiation does not affect surrounding tissue and also seems to activate the body’s healing mechanisms.”
He stressed that surgery remains the “gold standard” as it removes all the cancerous tissue but said those who cannot have it for various reasons could benefit.
