A short historical report is given on the formation of the one-interstitial model (OIM) which was introduced by F. Seitz and H. B. Huntington in the late fifties. In the early sixties J. F. Brinkman and A. Seeger suggested the two-interstitial model (TIM) after many new experimental and theoretical results became available and raised a continous discussion on the validity of the two models.
A few of the many experimental results obtained on radiation damage in fcc metals and alloys over the last thirty-five years are discussed and it is shown that all these results only support the TIM. It could further be shown that the migration activation energies of point defects decrease with increasing high energy particle flux, that dynamic crowdions can change lattice sites 50,000 times before their energy is dissipated to the lattice, that the recombination volume α between self-interstitials and vacancies is one order of magnitude larger than assumed so far etc.. These and many other features of point defects are discussed and the extended version of the TIM, namely the modified two interstitial model (MTIM), is presented.
It is further shown that the rate equations to calculate point defect concentrations built up during irradiation with high energy particles are powerful ways to understand and explain radiation damage. However, the advocates of the OIM in the past used only the steady state solutions of the rate equations which are only mathematical solutions and do not reflect physical reality.
Correlated self-interstitial-vacancy pairs annihilate in recovery stages I and II and correlated crowdion-vacancy pairs annihilate in the broad recovery sub-stage ID in such materials in which crowdions are stable. Crowdions migrate in the tiny sub-recovery stage IE, self-interstitials in recovery stage III, and vacancies in recovery stage IV.
The implications and importance of the application of the MTIM for the development of radiation resistant materials are outlined.