5. Recommended Values for Key Data

This Section presents the analyses that support new recommendations for the numerical values, and the associated uncertainties, of the key parameters considered in this Report. These key data include the mean excitation energies for air, Iair, and for graphite, Ig, that are needed in the determination of stopping-power ratios, the average energy to create an ion pair in air, Wair, which is needed for the determination of air kerma, and the mean excitation energy for liquid water, Iw, which is central to calculations that support charged-particle therapy and is important for certain factors entering in the determination of absorbed dose in water. Recommendations are also given for the humidity correction factor, kh, for air-filled ionization chambers, the ferric ion yield, G(Fe3þ), required for Fricke dosimetry and the heat defect, h, for graphite and water calorimetry. Data for kW, the correction in photon and electron beams at low energies for the deviation of Wair from the high-energy value, and for kii, the correction to the measured charge due to the ion pairs created by an incident photon, are also summarized.