Plutonium

Plutonium (IPA: /ˌpluːˈtəʊniəm/) is a radioactive, metallic chemical element. It has the symbol Pu and the atomic number 94. It is the element used in most modern nuclear weapons. The most significant isotope of plutonium is 239Pu, with a half-life of 24,100 years. It can be made from natural uranium and is fissile. The most stable isotope is 244Pu, with a half-life of about 80 million years, long enough to be found in extremely small quantities in nature. In fact, 244Pu is the nucleon-richest atom that naturally occurs in the Earth's crust, albeit in small traces.