Irradiation-enhanced diffusion

Worldwide enhancements of aerosols in the stratosphere are observed after big volcanic eruptions (i.e., by the volcano Pinatubo in 1991), which led to a decrease in direct solar irradiance and an increase in diffuse irradiance. This effect could be measured especially well at a high mountain station, where the disturbance by urban aerosol pollution is very small. In this case, diffuse solar radiation was increased nearly twofold, while global (direct and diffuse) radiation was reduced by about 4% [34]. 

D S is the irradiation enhanced diffusion coefficient of chromium in iron according to... 

Since the details of these equations are explained elsewhere, only key ideas are briefly described here. One of these is to classify the solute atom clusters into irradiation-induced clusters and irradiation-enhanced clusters. Irradiation-induced clusters correspond to solute atom clusters with or without Cu atoms, whose formation mechanism is assumed to be the segregation of solute atoms based on point defect cluster or matrix damage (heterogeneous nucleation). On the other hand, the irradiation-enhanced clusters correspond to so-called CRPs (Cu-rich precipitates) or CELs (Cu-enriched clusters), and the formation mechanism is the clustering of Cu atoms above the solubility limit enhanced by the excess vacancies introduced by irradiation. This model also assumes that the formation of solute atom clusters and matrix damage is not independent to each other, which is a very different model from the conventional two-feature models as described in the previous sections. Another key idea is the introduction of a concept of a thermal vacancy contribution in the diffusivity model. This idea is essentially identical to that shown in Rg. 11.11. This is a direct modeling of the results of atomic-level computer simulations. ... 

Radiation-enhanced diffusion The enhancement of the diffusion rate by radiation damage from heavy-particle irradiation, which generates lattice defects in the near-surface region. 

For elemental solids and stoichiometric compound crystals, the primary influence of irradiation on their kinetic behavior is due to the increase in Acv(s Ac,). We would expect the enhancement in the component diffusion to be in proportion to the increase in the (average) defect concentrations, thus influencing all homogeneous, inhomogeneous, and heterogeneous solid state reactions. 

By 7-irradiation, charge carriers are generated in the bulk of A1203 and Si02. By diffusion of the charge carriers to the surface of the solids, the decomposition of methanol is enhanced 63). 

Figures 2(a) and (b) show radiation induced conductivity (RIC) for the specimens with and without H as a function of ionizing dose rate at the first and second cycles, which were calculated using Ohm s law from the experimental data between from 0 to +10 V and the specimen volume. The conductivity increased with the increase of the ionizing dose rate. The values at the ionizing dose rate of 0.5 kGy/s became higher by two orders of magunitude than that without radiation, namely it is 0 Gy/s. The RIC with H is higher compared with that without H. Therefore, the RIC may be caused by electronic excitation as well as enhanced diffusion of H due to ionization irradiaion. After irradiation for 29 reactor full power days, the second reactor irradiation experiment was carried out for 27 days. The RIC with H at first cycle is almost same as that at second cycle. The RIC without H at several ionizing dose rate decreased by about one order of magnitude.

---