A picocurie is a unit of measure for radiation. A curie (named after French physicist Marie Curie) is a way of measuring radioactive decay or disintegration, and it equals 3.7 x 1010 disintegrations per second. "Pico" means "trillionth," so a picocurie is a trillionth of a curie, or one-trillionth of 37 billion disintegrations per second. To put this in perspective, a house having 4 picocuries of radon per liter of air (4 pCi/l) has about 8 or 9 atoms of radon decaying every minute in every liter of air inside the house. A 1,000 square foot house with 4 pCi/l of radon has nearly 2 million atoms decaying in it every minute.