Cluster arrangement of point defects in γ-rradiated LiF

part of the paper compares changes in texture and pore size distributions. The results are (a) during heat treatment a significant growth of the energetically preferred bigger pores, consuming the small ones, can be noted, (b) the changes in texture increase with increasing concentration in vacancies or small vacancy clusters and internal or external stresses, (c) creep in pyrocarbon leads to a strong decrease in pore concentration of 10 A pores which in turn should lead to a decrease in creep processes. Study on matrix material and graphite: In contrast to graphite, matrix material additionally contains disordered, non-graphitized binder regions. In these regions an irradiation-induced graphitization takes place at irradiation temperatures far below the usual graphitization temperature. "l-his graphitization leads to a higher order in the binder which should be perceptible by a decrease in vacancy-cluster concentration. The change of microporosity in matrix material and graphite was measured as a function of the dose of fast neutrons. The results are: The concentration of small pores is reduced in the binder by irradiation-induced graphitization. The final value is caused by a balance of two contrarily acting processes. The production of new defects during irradiation leads to a lower state of order in the material. On the other hand, the degree of order increases by the use of irradiation-produced Frenkel defects for atomistic transport processes. Therefore in the low-ordered binder an irradiation-induced graphitization is predominant at low doses. With increasing dose and order an increasing disordering process is superimposed until an equilibrium is reached. The concentration of vacancy clusters therefore decreases to a limiting value. Unlike in matrix material, the order in graphite is reduced: the concentration of vacancy clusters increases from the beginning of the irradiation.