From Gizmodo, here’s what happens when you stick your head in an operating particle accelerator:
On July 13, 1978, Bugorski was checking a malfunctioning piece of equipment. As he was leaning over the piece of equipment, he stuck his head through the part of the accelerator that the proton beam was running through. 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. An example where this is commonly used is in X-rays. For reference, 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 about the speed of light.
You know you’re not supposed to do that, right?