What is polonium?

Swiss scientists have found 18 times the normal amount of polonium in samples of former Palestinian leader Yasser Arafat's body.

That has led them to conclude with 83 percent certainty that Arafat was poisoned — a theory that surfaced immediately when he died in 2004, after being bunkered in his Ramallah compound in the West Bank.

At the time, doctors were unable to tell why Arafat began experiencing nausea, bouts of vomiting, and abdominal pain before finally dying in a French hospital. Previous medical records simply stated that he died from "a bleeding disorder caused by an unidentified infection."

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His body was exhumed earlier this year after Al Jazeera found traces of polonium in his clothes while in the process of making a documentary about his death. The most recent study provided no clues as to who might have murdered Arafat, but it's likely to stoke rumors pushed by his wife Suha, who has publicly cast suspicion on Israel. (The Israeli government denies that it had anything to do with Arafat's death.)

Seeing as it isn't the most common murder weapon, here is a brief guide to everything you need to know about polonium.

What is polonium?

It's an extremely rare substance found in uranium ore, formally known as polonium-210. The name comes from the country, Poland, where scientists Marie and Pierre Curie discovered it in 1898.

Why is it so dangerous?

It emits deadly alpha radiation particles that, according to the CDC, "damage or destroy genetic material in cells inside the body." While skin protects against exposure to polonium, less than a gram can kill someone if it is ingested or inhaled, or enters the bloodstream through a wound.

In smaller amounts, it can cause lung cancer. Large doses, however, can start affecting major organs like the liver, kidney, and bone marrow within hours of ingestion, eventually resulting in acute radiation sickness, followed by organ failure and death.

Has it been used as a weapon before?

Yes. In 2006, Alexander V. Litvinenko, a former K.G.B. officer, died three weeks after drinking tea laced with polonium. His assassination created tension between the United Kingdom, where he had been granted asylum, and the Russian government, which he had been criticizing. The Kremlin refused to turn over to British authorities the main suspect in the murder, former K.G.B. bodyguard Andrei K. Lugovoi.

Is it easy to obtain?

Absolutely not, which is why the presence of polonium points to the involvement of a larger player — especially one with nuclear capabilities. Only three ounces of the stuff is produced each year, according to the U.S. Nuclear Regulatory Commission, primarily for the purpose of eliminating static in industrial machinery in nuclear reactors.

Why use polonium?

It kills in such small doses — equal to a single grain of salt — that it can't be tasted. Not only that, but alpha particles don't set off radiation detectors, making polonium easier to smuggle into secure areas.

As Wired noted last year, its effects are also felt gradually. That means it's a lot harder to pinpoint when, exactly, someone was poisoned with polonium. It's also so rare that investigators don't usually screen for it.

Of course, when it is used, its scarcity becomes a vital clue — only so many people in the world can get their hands on it.