Answer to Question #6833 Submitted to "Ask the Experts"

So far as I am aware, following the poisoning of Khokhlov, there was never a positive identification, or at least a public disclosure, of a particular isotope of thallium as the culprit. In fact, many of the symptoms that Khokhlov suffered were consistent with stable thallium poisoning. These included abdominal pain and vomiting, hair loss (in clumps), eye problems, and some mouth and skin rashes and lesions. From what I understand, some additional symptoms that included degradation in the blood-forming system and the immune system led some American consultants to promote the idea that radioactive thallium was likely responsible.

If that were true, the most likely candidate, in my opinion, would have been ²⁰⁴Tl, a species that can be produced readily by neutron activation of stable thallium in a nuclear reactor. Russia's first nuclear reactor was built in 1954, so the technology was presumably available to prepare this isotope in 1957 when Khokhlov was poisoned. Thallium-204 is a pure beta emitter (maximum energy of 0.76 MeV) with a 3.8-year physical half-life. It is possible that stable thallium was treated in a neutron field to produce ²⁰⁴Tl, although almost all the mass of the thallium present after neutron irradiation would still have been stable, with relatively few atoms having been converted to the radioisotope.

You can find a large number of Web pages that discuss aspects of the Khokhlov case by typing "Khokhlov thallium poisoning" into any of the common search engines. Here are some links to a few representative ones. The first one includes a picture of Kohkhlov prior to his poisoning.

• Hoover Institution - Hoover Digest - Dark Memories
  
  
• I Led KGB Hit Squad
  
  
• Russia: The Speculation About Thallium Poisoning
  
  
• Russia, Litvinenko Assassination - JRL 2-12-07

Sorry I can't be completely definitive in answering your question.

George Chabot, PhD, CHP