Differential absorption is when a substance with mixed components absorbs and reflects radiation at different rates. It is used in medical imaging, atmospheric gas measurements, space studies, soil and rock analysis, and archaeology. Technicians can adjust the clarity and quality of the image by using different types of radiation or by altering the intensity. In physics, scientists use differential absorption with techniques such as LIDAR to learn more about the composition of the atmosphere. In soil sciences and geology, differential absorption can be a useful way to gather data about what’s happening beneath the surface of the earth or ocean.
Differential absorption is a phenomenon in which a substance with mixed components absorbs and reflects radiation at different rates due to the different composition of the components. A classic example of this can be seen in X-ray imaging, where a doctor can take a picture of the inside of a patient’s body by irradiating the patient to expose the film. Body structures are visible on film because they absorb X-rays to varying degrees; bone, for example, absorbs a lot of X-rays and so the film is not exposed to show the patient’s bones.
Medical imaging isn’t the only field where differential absorption is useful. It can also be useful for tasks such as measuring atmospheric gas concentrations, studying remote events in space, and analyzing soil and rock formations. In all of these cases, people rely on the fact that materials absorb and reflect radiation at different rates to gather data.
The technician can adjust the clarity and quality of the image by using different types of radiation or by altering the intensity. In medical imaging, people have to strike a balance between getting a good picture and putting the patient in danger. In X-ray imaging, for example, higher resolution can be achieved, but this would expose the patient to unacceptably high levels of radiation. Scientific researchers who exploit differential absorption must also consider the effects of radiation on the experiment.
In physics, scientists use differential absorption with techniques such as light sensing and distance (LIDAR) to learn more about the composition of the atmosphere. This involves sending pulses of light to an area of interest and reading the reflected light as it returns. Some of the gases in the atmosphere will absorb light while others will reflect it, and the amount of scattering that occurs can tell researchers which gases are present. They can compare data from other sites to study topics such as the ozone layer, meteorology and the effects of pollution on the atmosphere.
In soil sciences and geology, differential absorption can be a useful way to gather data about what’s happening beneath the surface of the earth or ocean. Archaeologists also use this technique to study buried sites. Most commonly, this involves using a device that emits sound waves. The device passes over the surface, and the reflected sound waves tell technicians what’s underneath, since things like rock formations, wrecks or buried buildings will reflect sound waves at different speeds relative to the ground. Different terrain types will also have different reflection patterns.
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