On July 13, 1978, Russian scientist Anatoli Petrovich Bugorski became the only person to ever stick his head in a running particle accelerator. A researcher at the Institute for High Energy Physics in Protvino, Bugorski was checking a malfunctioning piece of equipment on the Soviet particle accelerator, Synchrotron U-70, when he accidentally put his head directly in the path of the machine’s proton beam. He reported seeing a flash that was “brighter than a thousand suns,” but did not feel any pain when this happened.
The beam itself measured 2000 gray as it entered Bugorski’s skull and about 3000 gray when it exited on the other side. A “gray” is an SI unit of energy absorbed from ionizing radiation. One gray is equal to the absorption of one joule of radiation energy by one kilogram of matter. Absorption of over 5 grays at any time usually leads to death within 14 days. However, no one before had ever experienced radiation in the form of a proton beam moving at nearly the speed of light.
via Mental Floss