Gray, or Grey, any color formed by blending black and white. Gray tones range from nearly white to nearly black. The many tiny dots of black and white in a halftone reproduction of a photograph produce gray tones.
Atoms: the building blocks of life and the universe. We're all made of these microscopic bits of matter, but how many does it take to make a complete human being? And exactly what kinds of atoms do we have inside us?
Nuclear materials get used in many forms of nuclear medicine -- everything from PET scans to chemotherapy uses them. Learn how nuclear medicine works.