Radiation Damage of Diamond by Electron and Gamma Irradiation

Abstract

Diamond is an exceptionally radiation-hard material, but the main mechanisms by which lattice damage results from irradiation of high-energy particles and photons are not well understood. Models of radiation damage in diamond have been built up for both electron and gamma irradiation using Monte Carlo computer simulations. The energies investigated ranged from 0.25 to 10 MeV for electron irradiation and 1 to 15 MeV for gamma irradiation. Electrons have a low collision cross-section with carbon atoms, and therefore much of their energy is dissipated in ionisation before the electron displaces an atom. Gamma radiation causes damage by the indirect process of generating electrons (by Compton scattering and pair production) which then displace atoms (and ionise the material). The knock-on atom may cause further damage by displacing further atoms. However, both electron and gamma irradiation form predominantly isolated vacancies and interstitial pairs (Frenkel pairs). The range of 1 MeV electrons in diamond is about 1.3 mm with a nearly constant damage profile up to this cut-off. The range of gamma photons is much greater, with about 85% of 1 MeV photons passing through a 5 mm diamond without causing any damage. The total damage rates were calculated to vary between 0.01 and 5.15 vacancies per incident electron and between 0.02 and 6.10 vacancies per photon over the energy ranges investigated.