July 4, 2012

expert reaction to claims of polonium-210 being used to poison Yasser Arafat

Traces of the radioactive compound polonium-210 were found on clothes of ex-Palestinian leader Yasser Arafat, leading to claims that poisoning may have been the cause of his death.

Prof Paddy Regan, Professor of Nuclear Physics and Director of the MSc course in Radiation and Environmental Protection at the University of Surrey, said:

“There is not enough information in the public domain to be clear about whether polonium-210 was, or indeed could have been, the cause of death. What we do know is that the decay half-life of polonium-210 is 138 days. This means that the polonium allegedly found in Mr Arafat’s urine stain would have been about 1 million times more radioactive at the time of his death in November 2004 than it is now i.e. assuming that the polonium-210 in the stain all comes from the same original source then you can extrapolate back in time and calculate that the polonium-210 activity would have been around two hundred thousand decays per second, which is very high indeed.

“We can say that the current level reported now of 5 decays per second would not be enough to kill a human. You would need a level of more than about a milliCurie (which corresponds to tens of millions of polonium-210 radioactive decays per second for the entire source or so to be fatal if the substance is ingested internally. However, we cannot link the 200,000 decays per second extrapolated back to the sample with the necessary tens of millions of decays per second over a whole body needed to kill. The problem is that we would be making assumptions about how much of the original source had got into the bladder and then into the urine. Someone would need to establish the pathway that any polonium-210 had taken and verify all the figures.

“Furthermore, whilst the experimental signature for the presence of polonium-210 is a characteristic alpha-particle energy of 5.3 MeV, it should be noted that polonium-210 is also present in the natural radioactive background as a part of the uranium-238 natural decay chain. Part of this decay chain is an isotope of lead (lead-210) which decays to 210-bismuth and then 210-polonium. If there was any external contamination from these naturally occurring radioactive sources, which are ubiquitous since this material is constantly being created from the natural decay of the uranium decay chain (which includes radon gas), these might lead to an erroneous conclusion about the amount of polonium-210 present on Mr. Arafat’s body at the time of his death.

“If the polonium-210 came from the natural decay chains, one might expect it to be present with other members of the radioactive decay chains and also to be present at similar levels in other places of his body. Polonium-210 also arises from the natural decay of radium-226 which, for example, was used in some luminous watch dials. In any case, all such ‘natural’ sources must be ruled out before any conclusion can be made as to the use of polonium-210 as a murder weapon.”