Bucky Anti-Scatter Grid

The first radiographs were foggy and nobody could say why. The beam went through the patient and onto the plate, so the picture should have been a clean shadow - but the thicker the part being photographed, the greyer and more washed-out the result, until an abdomen was barely readable at all. The cause is that a body does not simply absorb X-rays or pass them. It **scatters** them. A photon can strike an atom, change direction, and continue on to the plate carrying no information about where it came from. Every one of those is a grey dot in the wrong place, and in a thick body they outnumber the photons that travelled straight. Gustav Bucky's answer, in **US 1,164,987** "Method of and Apparatus for Projecting Röntgen Images" - filed 3. February 1914, granted 21. December 1915 - is beautifully simple. You cannot tell a scattered photon from a straight one by looking at it. But you CAN tell them apart by the direction they arrive from, because the straight ones all come from one point: the tube. So he put a grid in front of the plate: "a number of chambers having walls of a form to obstruct passage of secondary Rontgen rays", with the walls parallel to the primary beam and intersecting at the anticathode. Anything travelling toward the plate from the focal spot passes down a chamber and through. Anything arriving at an angle hits a wall and stops. **You will build this with light, and it works identically.** Scatter is simply light arriving from the wrong direction, and a grid that passes light from one point while blocking light from everywhere else is the same device. You will build a focused grid, measure its acceptance angle, and find out for yourself how brutally a focused grid punishes being at the wrong distance - the fault that still ruins radiographs today. One thing the grid cannot do is hide itself: a stationary grid always prints its own strips across the picture. Hollis Potter's answer in 1920 was to move it during the exposure so the lines blur away, and the combination has been called the Potter-Bucky diaphragm ever since.