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In physics, backscattering refers to the reflection of energy or particles back towards the source of an electromagnetic wave after it comes into contact with an object. There are a number of fields that make frequent use of the principles of backscattering, including meteorology, photography, and medical science. By analysis of the way an object scatters radiation, scientists in these and other fields can gain information about the composition of the object.
When an object or particle is struck by electromagnetic radiation, such as X-rays, some of the radiation is reflected back towards the source of the radiation. The radiation that bounces back in this direction is known as the backscatter. In most cases, objects will scatter radiation in all directions, and an analysis of how the object scatters radiation can give scientists information about that object. In many cases, backscattering is used to gather information because the device that emits radiation and the device that detects the scattering of that radiation are located on the same side of the target. In most cases, information can be gleaned from the way the radiation scatters around the opposite side of the object, it’s just that there isn't a device on that side to collect the information.
In medicine, the principles of backscattering may be used to create special types of X-ray images. In a typical X-ray, a machine emits a strong beam of radiation at a subject, who stands between the machine and the collection device. The radiation that is not absorbed by the subject reaches the X-ray film and creates an image of the subject. In a backscattering X-ray, on the other hand, the emitter and the collector are located on the same side of the subject. The collector gathers information from the subject as the radiation is absorbed by and reflected back off of it.
Meteorology also makes frequent use of the principles of backscattering. The radar used to provide color coded images of current precipitation is possible because different types of precipitation scatter radiation in different ways. Snow, for instance, produces very little backscattering, while heavy rain or hail reflect large amounts of radiation back towards the radar station.
Backscattering is also important to the field of fiber optics. When a stream of radiation travels down a fiber optic cable for a long distance, that signal will eventually weaken to the point that it is unreadable. In this case, backscattering is responsible for the deterioration of the signal because a certain amount of radiation is reflected back the way it came each time it bounces off the cable's walls.