'In November 2006 former KGB operative Alexander Litvinenko died in a London hospital in what had all the hallmarks of a cold war–style assassination. Despite the intrigue surrounding Litvinenko's death, the poison that killed him, a rare radioactive isotope called polonium 210, is far more widespread than many of us realize: people worldwide smoke almost six trillion cigarettes a year, and each one delivers a small amount of polonium 210 to the lungs. Puff by puff, the poison builds up to the equivalent radiation dosage of 300 chest x-rays a year for a person who smokes one and a half packs a day.'

This is a quote form an article in the Scientific American Magazine January 2011

The article is interesting - read it and discuss with your classmates!

Smoking increases the risk of cancer - inhaling radiactive particles provides a mechanism by which we can understand how this happens.