Polyenergetic

Polyenergetic refers to a system or signal that contains multiple energy components rather than a single energy value. In physics and engineering, the term is commonly applied to radiation sources and particle beams whose emitted or incident particles span a spectrum of energies, rather than being monoenergetic. Examples include X-ray tubes and bremsstrahlung sources, gamma-ray sources with broad spectra, and neutron or charged-particle beams produced by accelerators. In contrast, a monoenergetic source emits particles at approximately one energy.

In imaging and radiation therapy, polyenergetic spectra require energy-resolved modeling because material attenuation and dose deposition depend on energy. The transmission through matter is integrated over the energy spectrum weighted by the source spectrum and energy-dependent attenuation coefficients μ(E). This leads to phenomena such as beam hardening in CT, where the effective spectrum shifts to higher energies as it passes through matter. Spectral imaging methods, such as dual-energy or photon-counting CT, exploit the polyenergetic nature to discriminate materials.

Polyenergetic modeling is essential in shielding design, dosimetry, and radiation transport simulations, where accurate spectra improve prediction of dose, activation, or shield performance. It is common to approximate polyenergetic fields with an effective or characteristic energy or by decomposing the spectrum into a small number of representative energies, but such approximations may introduce errors if energy dependence is strong.