Contributor Jeremy Putley refers us to the following item in the London Review of Books. Jeremy writes: "I find this article interesting, as having been written by a professor emeritus of theoretical physics who knows the subject better than most. Professor Dombey hypothesizes that polonium-210 was first tried out, experimentally, on the Chechen prisoner, Lecha Islamov, murdered by his jailers in 2004, and then used on Roman Tsepov also in 2004. When Putin is eventually succeeded by an honourable president in Russia (at an unknowable future date) perhaps the truth about Putin’s murders will then become known."

The word ‘radioactive’ was first used in public on 18 July 1898, when Marie Curie and her husband, Pierre, reported to the French Academy of Sciences on the progress of their work on becquerel rays – what we would now call ionising radiation. The Curies had subjected pitchblende, a black mineral composed largely of uranium dioxide, to repeated heating, then dissolved the residue in acid. The process yielded a substance four hundred times more radioactive than uranium; they named it polonium, after Marie Curie’s country of origin. Later that year, they isolated radium.

The hazards of working with radioactive materials initially seemed restricted to occasional fatigue and skin burns but in November 1925 Nobus Yamada, who had worked in the Curies’ laboratory on the preparation of polonium sources, fainted suddenly a few days after his return to Japan. He died eighteen months later. In the summer of 1927, the Curies’ daughter Irène wrote that Sonia Cotelle, a Polish researcher who had also been working with polonium, ‘was in very bad health’: she had stomach problems and had suffered ‘an extremely rapid loss of hair’. Cotelle continued work despite this for a few more years until a glass containing polonium shattered in her face. She died two weeks later. Yamada and Cotelle are the earliest known victims of polonium poisoning.

On 1 November last year, the Russian exile and former intelligence agent Alexander Litvinenko began vomiting after drinking a cup of tea at a London hotel. He was taken to a local hospital. His symptoms – hair loss and blistering in the mouth – seemed to indicate radiation poisoning, but a Geiger counter showed no signal. He was transferred to University College Hospital, where he was placed in intensive care and underwent further tests. Amit Nathwani, the consultant haematologist in charge of his case, established that his bone marrow function had failed: another symptom of acute radiation poisoning. He died on 23 November.

Litvinenko’s murderers should not have carried out their operation in London. Almost anywhere else, the death would have been merely suspicious and its cause would have remained unknown. But UCH is not only a leading teaching hospital; it is also associated with University College London, which has a Department of Medical Physics with a strong radiation physics group. A network of haematologists, radiation experts and toxicologists was assembled from UCH and other major London teaching hospitals, in an attempt to isolate the cause of the illness, and when radiation poisoning was suspected, the police sent Litvinenko’s blood and urine samples for analysis to the Atomic Weapons Establishment at Aldermaston.

Three distinct forms of radiation are emitted by radioactive substances: alpha radiation, which is composed of helium nuclei; beta radiation, which consists of electrons; and gamma radiation, electromagnetic radiation of higher energy than X-rays and carrying no electric charge. Alpha radiation, which is emitted by polonium and radium, is stopped by a thin layer of matter – skin, for example – while beta and gamma radiation can penetrate tissue. Geiger counters detect beta and gamma radiation; but the detection of alpha radiation requires specialised equipment such as that used at Aldermaston. The polonium discovered by the Curies is a mixture of isotopes: more than 20 polonium isotopes are now known, ranging from polonium-184 to polonium-218. The polonium that killed Litvinenko, however, was not refined from pitchblende, but was the pure isotope Po-210, obtained by neutron irradiation of bismuth-209 in a nuclear reactor. Aldermaston suspected Po-210 when they detected a weak gamma signal of the right energy. Polonium sticks to metal and a silver disc was used at Aldermaston to collect an enriched sample, which produced alpha particles with an energy of 5.3 million electronvolts, the signature of Po-210 decay: this definitively identified the poison.

More than 95 per cent of the world’s Po-210 is made in one place: the nuclear weapon assembly plant of Avangard in the formerly closed Soviet nuclear city of Arzamas-16, now called by its original name, Sarov. Russia exports about eight grams of Po-210 a month to Western countries, where it is used in minute quantities in devices that remove static charge in industrial processes. Po-210 is enormously radioactive: one gram emits 140 watts, enough to power two light bulbs; the isotope can be used as a lightweight power source in spacecraft. One picogram (one millionth of a millionth of a gram) of Po-210 has an activity of more than 100 alpha particle counts per second, so even unimaginably small amounts will register radiation on an alpha-particle counter. The investigation into Litvinenko’s death found a trail of the isotope extending from Moscow to London via Hamburg. In May, Scotland Yard announced that Andrei Lugovoi, a former KGB and FSB agent, was wanted for murder and the Crown Prosecution Service began extradition proceedings against him. Russia has refused extradition on the grounds that its constitution does not allow it, and has claimed that Litvinenko killed himself or was killed by his patron Boris Berezovsky.

It is clear, however, that only a state-sponsored group or rogue elements within a state-sponsored group, could have had access to Po-210, and there can be little doubt that in this case the state was Russia. It is well known that the KGB specialised in poisoning: Laboratory No. 12 was founded in 1921 to carry out research in this area. The KGB has poisoned people in Britain before. In 1978, the Bulgarian journalist Georgi Markov was killed with ricin, injected by means of a specially adapted umbrella. In April 2005 Boris Volodarsky, a former Soviet military intelligence officer now living in the West, wrote an article for the Wall Street Journal in which he listed some recent poisonings that he claimed had been carried out by the FSB. These included the use of a dioxin-based poison on Viktor Yushchenko during the presidential election campaign in Ukraine in 2004, and the 2002 killing of a Chechen-based militant known as Khattab by means of a poisoned letter. Ivan Rybkin, who stood for the presidency against Putin in February 2004, disappeared for several days during the campaign and when he reappeared claimed the FSB had drugged him; in September 2004, the journalist Anna Politkovskaya, who was murdered in Moscow shortly before Litvinenko became ill, lost consciousness after drinking tea aboard a flight to Beslan (she later asserted that FSB agents on the plane had poisoned her); and the Russian MP and human rights activist Yuri Shchekochikhin died suddenly in 2003 from a mysterious illness which caused his skin to fall off and his internal organs to swell up – probably the result of radioactive thallium poisoning.

None of this, needless to say, proves that Putin ordered Litvinenko’s assassination, as Litvinenko claimed on his deathbed. However, a new law – passed by the Duma in June 2006 – gives the FSB authority to send commandos abroad to assassinate ‘terrorist groups’, and this power is to be used only at the discretion of the president. In Death of a Dissident, Alex Goldfarb and Marina Litvinenko present further evidence which, they claim, shows that Putin was personally responsible for targeting the London-based group of Russian exiles centred on Boris Berezovsky. Some of it is compelling, in particular their argument that the real-time monitoring of phone calls between Russia and London (as distinct from calls being recorded and listened to later) could only have been authorised at a very high level: in the Russian system that means the presidential office. They also claim that the use of such an unusual method of assassination would have been intended to make clear to Russian exiles in London the extent of the power of the Russian state.

The use of Po-210 as a poison requires a detailed understanding of its properties. During the Cold War, both Soviet and American scientists explored the effects of Po-210 on animals and humans. In the US, the Atomic Energy Commission sponsored experiments at the University of Rochester on the use of injections of Po-210 to treat patients with terminal cancer, and also studied its effects on animals. In the Soviet Union more detailed studies were made of Po-210 as a poison. Its ‘devastating effects were studied in the 1960s at a Moscow institute where the isotope was administered to dogs, rabbits and rats’, according to Boris Zhuikov, the head of the radioisotope laboratory in the Nuclear Studies Institute of the Russian Academy of Sciences, in an interview with the Washington Post. ‘If someone hates, really hates,’ he added, ‘then it’s a good material’ to use: ‘This is real suffering.’ Although alpha particles do not penetrate skin, if an alpha emitter is ingested it can be lethal. In March, the Radiation Protection Division of the Health Protection Agency published a paper, ‘Polonium-210 as a Poison’, which estimated that 20 micrograms was required to kill a man weighing 70 kg. A little more than this was probably used to kill Litvinenko.

But theoretical knowledge wouldn’t have been sufficient. Tests on animals would be useful in establishing the dosage for humans, but are not finally reliable. A senior radiation expert, one of those consulted by the Health Protection Agency over the Po-210 contamination in London, told me that tests would have been carried out on humans as well as animals in order to determine the efficacy of the poison. An assassination attempt, especially one to be carried out overseas, would require a carefully tested poison: the amount of Po-210 would need to be enough to kill but not to cause a major public health incident. Just as the KGB developed the ricin capsule in the Markov case, the best method of administering Po-210 would have had to be studied. It is not yet known how this was done: it could have been a drop of liquid from a fountain pen or a grain of specially prepared sugar dissolved in Litvinenko’s tea.

So who was Po-210 tested on? In April 2004, it was reported that Lecha Islamov, a Chechen guerrilla commander serving a nine-year prison sentence, had died after being admitted to hospital in Volgograd with a mysterious illness. ‘Sources close to the convict,’ ran a report in the Chechnya Weekly, ‘told the online newspaper Vremya Novostei that they suspect he may have been poisoned by Russia’s security agencies . . . Islamov’s symptoms – including hair loss and massive blisters – were said to be inexplicable to the doctors who have been trying to treat him.’ Islamov’s relatives said that he’d told them his jailers had summoned him several days before his death for an ‘informal conversation’, during which he was given a snack and some tea. ‘He began to feel ill within five minutes,’ they said, ‘as he was being taken back to his cell.’

A second possible precedent for the use of Po-210 as a poison was discussed on the BBC’s File on 4 in February. Julian O’Halloran reported that in September 2004 a man was taken to Hospital No. 31 in St Petersburg, which used to be a clinic for the Communist elite. ‘The man, who had a background in security, had fallen ill two weeks earlier. At first it looked like food poisoning, but after a brief apparent recovery, the man’s symptoms grew much worse, leaving his doctors utterly perplexed.’ One of the doctors said that the patient ‘was very feeble. He stopped vomiting and the diarrhoea became less frequent, but there was still no sign of toxic infection. It was a poisoning without a poison. What we didn’t like from the start was the low level of white blood cells. It was as if his immune system was switched off.’ The patient was Roman Tsepov, who was, O’Halloran continued,

in the security and bodyguard business. In the 1990s, he’d guarded the city’s powerful mayor and even the local man who, seven years ago, became Russia’s president: Vladimir Putin. Tsepov was reputed still to have friends in very high places. In September 2004 he was 42, busy and active, when he fell ill after a trip to Moscow . . . Hospital tests showed that Tsepov’s white blood cells, vital in fighting infection, had dropped to a seventh of their normal level. His physician, by now desperate, concluded the bone marrow was being destroyed.

Tsepov died soon afterwards; no cause of death was ever established.

If Tsepov and Islamov were victims of Po-210 poisoning, then – given that the isotope’s half-life is 138 days – the three and a quarter years since Islamov’s death would have reduced the level of Po-210 in his body by a factor of around 600, rather less in Tsepov’s case. If the dose of Po-210 administered was around 30 micrograms, then at least 50 nanograms would still be present in their bodies: enough to be detectable in tissue samples using alpha radiation spectrometry. So, in principle, it would be possible to establish whether polonium has killed others – but the Russian authorities would first have to allow the bodies to be exhumed.

Norman Dombey is a professor emeritus of theoretical physics at the University of Sussex.