Gamma Radiation

"She's thowing off interference, radiation. Nothing harmful. Low levels of gamma radiation." "That can be harmful."

- Erik Selvig and Nick Fury

Gamma Radiation is a type of nuclear radiation being tested by Bruce Banner when he was exposed turning him into the Hulk.

History
Bruce Banner experimented with gamma radiation and an accidentally turned himself into the Hulk in the process.

Erik Selvig mentions a scientist who experimented with gamma radiation. The Tesseract is mentioned to emit traces of gamma radiation, leading to the recruitment of Bruce Banner to assist in finding it.

Gamma radiation is one of the components of the Centipede serum, an item designated to give a person superhuman abilities: The rest of the components are the Extremis virus, a variation the of the Super Soldier Serum and technology from the Chitauri for injection.