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In physics, absorption refers to the process of one substance taking up matter or energy from another. This can occur in various forms, such as a liquid being absorbed by a solid (as in the case of ink being absorbed by blotting paper) or a gas being absorbed by a liquid (like ammonia being absorbed by water).
In the context of radiation and electromagnetic waves, absorption is the phenomenon by which a substance retains the energy of radiation at specific wavelengths. For example, a piece of blue glass absorbs all visible light except for the wavelengths in the blue part of the spectrum. Additionally, absorption can refer to the partial loss of energy that occurs when light and other electromagnetic waves pass through a medium.
In nuclear physics, absorption specifically denotes the capture of neutrons produced by fission in a reactor by elements such as boron. This process plays a crucial role in controlling and moderating nuclear reactions. Overall, absorption is a fundamental concept in physics, describing the uptake of matter or energy by a substance from another medium.