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.
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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