A study of inert-gas diffusion in ionic crystals and sinters with emphasis on the ion-bombardment technique

Abstract

The diffusion of inert gases in a series of ionic crystals and sinters has been studied. The main emphasis is put on the ion-bombardment technique, though data are also presented for α-recoil radon and fission-recoil xenon. A basic principle in interpreting the results has been to assign the pre-exponential factor an idealized range of values ( K o = 10 15 ± 1/ sec or Do ≈ 3 × 10 −1 ± 1 cm 2/ sec). In addition, the recently established system of stages is used: stage I = “damage diffusion”, stage II = “normal diffusion”, stage III = “bubble diffusion”. CaF2 is found to exhibit stages I and II, with ΔH normal lying between 60 and 70 kcal/mole for four different techniques. BaF 2 is examined only by ion bombardment: stage II dominates, with ΔH normal equal to about 58 kcal/mole. Although much work has been reported elsewhere for UO 2 and ThO 2, there is still marked disagreement. The two techniques used here require that ΔH normal be greater than about 90 kcal/mole for both materials. KCl is difficult to interpret because of the low vaporization temperature and the lack of agreement amongst different techniques. A possible interpretation is that it shows stages I and II, with ΔH normal lying between 38 and 46 kcal/mole. α- AU 2 O 3 shows a prominent release process at 550–1000° C which is believed not to be stage II. The true stage II seems, rather, to occur above 1000° C and to correspond to a ΔH normal of 89–95 kcal/mole.