In general, the average ratio between signals from electromagnetic and hadronic particles of the same incident energy is calorimeter- and energy-dependent, and for non-compensating calorimeters there is a higher response for electromagnetic particles, typically
For a compensating calorimeter, the electron/hadron signal ratio should be close to one.
Various phenomena in both active and passive layers of sampling calorimeters can be put to use to achieve , thus optimizing energy resolution: adjusting the relative thickness of absorber and active layers, using U238 as absorber for its fission capability for slow neutrons, or shielding the active layers by thin sheets of low-Z material to suppress contributions from soft photons in electromagnetic showers, are possible methods of active compensation (see [Wigmans91a]).
The photon absorption in the (high-Z) absorber material plays a significant role, and so does the conversion of low-energy neutrons into signal, e.g. by detection of de-excitation photons; the hydrogen content in the active medium is relevant here. For a detailed discussion, see [Wigmans91b].
If high resolution is not required during readout, e.g. for triggering, corrections corresponding to compensation may also be applied by an a posteriori algorithm (``off-line''), when the shower profile (mostly the longitudinal distribution) is known ( [Fesefeldt90a], [Andrieu93]). Just how much can be recovered by calibrations of this type, is strongly detector-dependent; [Borders94] has explored the possibilities for a specific non-compensating sampling calorimeter in detail, using individual weights for sampling layers.