The term RADIOACTIVITY, UNIT OF can be solved by the crossword solution CURIE (5 letters). This is a reference to Marie CURIE, a Polish-born French physicist and chemist who conducted pioneering research on radioactivity. She was the first woman to win a Nobel Prize, and the only person to win the Nobel Prize in two different sciences. She coined the term 'radioactivity' and developed the theory of radioactivity, which led to the discovery of the elements polonium and radium. The unit of radioactivity is named after her, and is known as the CURIE.