How do x rays see through things?

Xrays pass through most substinces. Various detectors can be used to detect the ammount of xrays that are sent from one side verses what is picked up on the other side. The difference can give you information about an object.

Xray radiation is created when high speed electrons hit a solid object. Basically high voltage electricity (usually 40,000 - 120,00 volts) is pushed across a gap from a cathode to an anode. The Anode is usually made of tungsten or other materials that can withstand high temperatures. The anode is usually spinning so that the target is not hit in the same spot over and over again, this allows the anode to last longer.

When the high voltage hits the target it releases xray radiation. Xray radiation is invisible, but it causes some elements to glow. The best used today are rare earth elements like yttrium and gadolinium.

The xrays travel through the patient's body and hit a film cassette that is treated with some of these rare earth elements and it glows wherever the xrays reach it. Some of your body blocks the xrays so the screen only glows in areas that is not entirely blocked. The thicker and more dense the body part the more xrays are blocked. Bone is very dense so it blocks more xrays than most any other tissue, so bones show up as clear areas on the film. The film is placed between these screens inside the cassette safe from regular light. So that the only light that reaches this film is the light created by the glowing elements bombarded by xray radiation.

The glowing of the elements bombarded by xrays causes the film to turn black and or grey depending on the amount of xrays that are blocked.

Modern xray machines have cassettes that use different phosphorus materials that keep a temporary image on the cassette then the cassette is read by a machine and creates a digital image. There is no film in these type of cassettes.

This is done because more and more facilities are not using film anymore. Storing xrays is cheaper and more efficient on computer hard drives as digital xrays. Because of the digital storage of xrays some xray machines do not use cassettes at all, only digital readers.