Polonium is one of the rarest natural elements with 10 grams of uranium containing a maximum of a billionth of a gram of polonium.

It is also a shadowy, silent killer.

Before Swiss scientists concluded that Palestinian leader Yasser Arafat died in 2004 due to polonium poisoning, the substance is believed to have caused the death of several scientists.

Despite the media attention it has drawn in recent years, only a few people have died from polonium poisoning. 

The highly radioactive material also known as Radium F, is rarely found outside military and scientific circles.

It is a rare but naturally occurring metalloid found in uranium ores that emits highly hazardous alpha, or positively charged, particles.

The last time polonium was named in a death, was in the case of Alexander Litvinenko, a former Russian spy and dissident.

He died in a London hospital in 2006 after falling ill following a meeting with two former KGB agents in a bar of London's Millennium Hotel.

Litvinenko who initially suffered from severe diarrhoea and vomiting, was diagnosed with a stomach infection.

But while in hospital, Litvinenko's white blood cell count plummeted, his liver started to fail and his hair fell out.

Doctors eventually identified poisoning from polonium that is believed to have been slipped into the Russian's drink.

In daily life, small doses of polonium exist in the soil and atmosphere, and even in the human body with little effect.

Small doses are also found in tobacco, derived from the soil and phosphate fertilisers used on tobacco plants.

The substance has been used industrially for its alpha radiation in research and medicine, and as a heating source for space components, but in those forms it is not conducive to easy poisoning.

In high doses however, it is highly toxic and if ingested or inhaled, causes damage to the body's tissues and organs.

It kills in ways that can be hard to diagnose until the radioactive element does its lethal work.

Polonium was discovered by Marie and Pierre Curie in 1898 while they were doing research in France on the cause of radioactivity in the mineral pitchblende, the chief ore-mineral source of uranium.

Marie Curie named the material after her homeland of Poland, which at the time was under Russian, Prussian and Austrian control and not recognised as an independent country.

Their discovery of polonium, radium and their work on radioactivity,  won the Curies the 1903 Nobel Prize in Physics, which they shared with Antoine Becquerel of France. 

Like many other pioneering researchers in the field of radioactivity, Marie Curie died in 1934 at the age 67 of leukaemia, brought on by her handling of radioactive materials.

It's not clear however, if she was the first victim of polonium.

It's believed that Curie's daugther, Irene Joliot-Curie, who was diagnosed with leukaemia in 1946 was a victim of polonium after a capsule containing the element burst in her laboratory, resulting in a long period of sickness.