Development of a Hybrid Alanine-calorimetry Absorbed-dose Standard for Linac Electron Beams

The NRC primary standard water calorimeter is well-established for measuring dose to water in cobalt-60, linac photon beams and high-energy linac electron beams. However, for lower-energy electron beams, given the short range of electrons and the physical dimensions of the calorimeter, it is impossible to perform measurements at the reference depths in water. Extending the measurement of absorbed dose to lower energy electron beams requires an alternative system. The goal is to establish a hybrid absorbed-dose standard for linac electron beams by calibrating alanine against secondary standard ionization chambers, with calibrations traceable to primary standard water calorimeter measurements in high-energy electron beams, and subsequently using alanine in low-energy electron beams to determine absorbed dose. Ionization chambers calibrated against alanine in electron beams yield results for beam quality conversion factors that are in good agreement (within 0.68% uncertainty) with literature data for the five ionization chambers investigated in this work.