On the choice of material for half-value-layer measurements for megavoltage x rays

The relative sensitivity of various materials for the measurement of half-value-layer thickness has been calculated for bremsstrahlung x ray spectra in the energy range 5-40 MeV. It is concluded that low-atomic-number materials such as water are more sensitive to changes in spectral quality of megavoltage x rays than high-atomic-number materials such as lead.