What is polonium?

Polonium is a chemical element in the periodic table that has the symbol Po and atomic number 84. A rare and highly radioactive metalloid, polonium is chemically similar to tellurium and bismuth, and it occurs in uranium ores. Polonium has been studied for possible use in heating spacecraft. It exists as a number of radio-isotopes.

A bit on the hisotry, sometimes referred to as “Radium F”, polonium was discovered by Marie Curie and her husband Pierre Curie in 1898[4] and was later named after Marie’s native land of Poland

From wikipedia.org.