In high energy physics experiments, an absorber is a block of material used to absorb some of the energy of an incident particle. Absorbers can be made of a variety of materials, depending on the purpose; lead and liquid hydrogen are common choices.
Most absorbers are used as part of a detector. See, for example, EM calorimeter .
A more recent use for absorbers is for ionization cooling . See International Muon Ionization Cooling Experiment.