Radiation 2006. In association with the Polymer Division, Royal Australian Chemical Institute. Incorporating the 21st AINSE Radiation Chemistry Conference and the 18th Radiation Biology Conference, conference handbook

Full text: Electrons and x-rays of energies higher than the threshold for photonuclear production in certain elements are currently used widely in radiotherapy and other radiation fields. Many attempts have been documented recently which are aimed at evaluating (mainly via simulation) the radiation dose specifically due to such nuclear secondary reactions in elements of human tissue. Since the dose from the activated substances persists after electrons and x-rays have been switched off, estimation of dose due to such radiations will be important for radiation protection procedures. Moreover, such radiation (photonuclear positron annihilation peak) could also be utilised for beam quality checks as part of quality assurance evaluations especially in radiotherapy. In this research, we investigated the photonuclear interactions of high-energy x-ray and electron beams typically used in radiotherapy (of energies ranging from 10 to 22MV and from 10 to 25MeV) produced by clinical type linear accelerators. The main elements irradiated are copper and oxygen in water molecules. Both copper and oxygen when irradiated by such high-energy radiations (with energy higher than their photonuclear reaction threshold) will emit a neutron and the isotope will become radioactive and will decay emitting a positron and the positron will annihilate emitting two gammas. One of these two 0.5MeV gammas generated from this annihilation are detected through a NaI scintillation crystal and the energy spectrum is obtained using a multi-channel analyser. A significant size photo peak is obtained with both the copper and oxygen irradiations at exactly 0.511MeV, which clearly indicates positron annihilation. The half-lives of the two isotopes are also determined to validate the identity of the two isotopes. Therefore, this simple method can be used to estimate the amount of neutrons generated by interactions with the patients body in such beams and it can also be used for detecting variations in the quality of the beam