A proton beam is invisible in our ordinary life, but we can see the behavior by letting it through a particular material. We let a proton beam through liquid scintillator, which glows when irradiated. The portion glowing bluish white light in the image below shows the distribution of proton beam. The proton beam is being irradiated out from the back. It may be a little difficult to make out the elliptical-looking image being observed from an angle, but it should look just about a perfect circle when observed squarely. The central white part is the high-intensity portion of proton beam, and the surrounding blue part shows the portion spread by scattering. We also prepared a moving image (mpeg 1:156kb) to compensate for the still one. Please click the image to play.