Interview by Folha de São Paulo newspaper (Brazil) With Berkeley Lab Nuclear Scientist Heino Nitsche on Polonium-210

Question: What exactly is the polonium-210 and how (in what forms) can it be found in nature? What does it take
to produce this substance? What is the most common use for it?

Answer: Polonium is element number 84 in the Periodic Table.  It was discovered by Marie and Pierre Curie in Paris in 1898.

Polonium-210 exists in nature.  It is a decay product of the natural decay of uranium-238, which exists in vast quantities in nature, not only in the form of large uranium ore deposits, but it (uranium) is ubiquitous in soils and water.

It is found in small amounts in tobacco smoke and is known to cause lung cancer.  Because tobacco is grown in soil, the plants take up the natural uranium, which decays in the tobacco to polonium-210, and this is inhaled by the smoker.

Polonium-210 is a radioactive element.  Generally, elements can have several isotopes, i.e., the same number of protons but different numbers of neutrons within the nucleus.  If the proton-to-neutron ratio is “off,” elements are unstable and decay to a different element. Polonium-210 decays by alpha decay, i.e., its nucleus emits helium ions and forms stable lead-206.    

Polonium-210 has a half life of 138.4 days. This means, if one has a fixed amount of polonium-210, after 138 days half of this amount is decayed to lead-206. One half of the remaining half is then again decayed after 138 days, leaving one quarter of the initial amount. This continues until all the polonium-210 has decayed.  After 10 half-lives, one-thousandth of the initial amount remains, that means that it is essentially gone after 1,384 days.

Polonium-210 can be produced in a cyclotron by the bombarding of natural stable bismuth-209 with high-energy neutrons.  In this reaction, radioactive bismuth-210 is formed, which is radioactive and decays by beta-minus decay to polonium-210.

Question: We know this substance is toxic when inhaled or ingested. In what quantities can the polonium-210 be lethal to humans? In what forms can it be used as a poison?

Answer:  The estimated lethal dose is 40 nanograms (40 billionth of a gram) for ingestion, and 10 nanograms for inhalation.  It could possibly be put into drinks and food.

Question: What effects does it have to the human body when it is inhaled or ingested? Is it true that it cannot be absorbed through skin?

Answer: Alpha radiation is absorbed by paper or skin.  To be harmful, it must be ingested or inhaled.

Question: How lethal can the polonium-210 be when compared to other radioactive substances?

Answer: This is a difficult question.  It depends on the specific activity, i.e, radioactivity per amount of mass.  Polonium-210 has 1.66 Exp14 decays per gram in one second (Bequerel per gram, Bq/g), plutonium-239 has 2.23Exp9 decays per gram in one second.  If we assume that the lethal dose only stems from the radioactivity and not from the toxicity of the metal, polonium-210 would be about 75,000 times more lethal than plutonium-239.

Question: How easy (or difficult, rather) is it to acquire this substance? Does every country have experiments or industrial uses for polonium-210 or is it restricted to a few places?

Answer: It is a controlled substance governed by the laws of individual countries. In the U.S.A., any radioactive substance can only be purchased by federal and state licensed companies.  Not every country has the technology to produce polonium-210.  In fact, there are relatively few countries where it can be produced.  Russia has all the requirements to produce this material.

Question: The U.K. is currently examining several offices and airplanes to try to detect traces of radiation, and they have already assessed that at least 12 places were contaminated. What real danger does this pose to people who work at these offices or traveled in these planes?

Answer: Because it is radioactive, the smallest quantities can be detected.  There is also the possibility that if the surveyors are not trained well enough that they can measure the “natural” polonium-210 coming from the decay of omnipresent uranium.   The danger depends on the amount.

Question: If a place is contaminated with radioactivity, how long does it take for it to “extinguish” by itself? Does it depend on the levels of radioactivity found? Can you give examples? How can you decontaminate a place from it?

Answer:  Polonium-210 has a half-life of 138.4 days. This means, if one has a fixed amount of polonium-210, after 138 days half of this amount is decayed to lead-206. One half of the remaining half is then again decayed after 138 days, leaving one quarter of the initial amount. This continues until all the polonium-210 has decayed.  After 10 half-lives, one-thousandth of the initial amount remains, that means that it is essentially gone after 1,384 days.

Question: Do you know of other occasions when the polonium-210 was used as a “weapon” or poison?

Answer: No.

Question: What other radioactive substances can be used as a “poison”?

Answer: Essentially all alpha-emitting radionuclides would have a damaging effect on the organism if they were either ingested or inhaled.  However, one has to consider that thousands of non-radioactive poisons also exist.

Question:  Can radioactive substances be easily transported? How could they have ended up in an airplane? If someone contaminated with radioactivity walks into a room, can he or she leave traces of it behind?

Answer: The transport of radioactive substances is strictly controlled.  If they or traces of them were found on an airplane, the persons smuggling them must have been externally contaminated.  Radioactivity can be detected so much better (1,000-100,000 times) than any non-radioactive toxic substance.  Even the smallest traces can be picked up if the (externally) contaminated person touched anything in a room.

Question: Although the polonium-210 is considered highly toxic, the Russian ex-spy poisoned with it, Alexander Litvinenko, survived for almost a month after he fell ill in the hospital. How long does it take for this substance to cause damage to the body?

Answer: Experience from animal studies with rats showed that it took about 30 days if they ingested about 8.7 nanograms per kg body mass. These data seem to agree with the fate of Litvinenko.