Stopping power of matter on electrons below 10 keV

In the research on the interaction of electrons with matters, specifically with solids, there has been a boundary at 10 keV so far. One of the reasons is that the stopping power equation by Bethe-Bloch has been widely used above 10 keV for a long time. This value of stopping power has been improved in various ways, and the one which well matches experimental values is arranged and used. Meanwhile, below 10 keV, all the loss processes can not be averaged like the Bethe-Block equation. The preparation of experimental specimens for the studies below 10 keV is also generally difficult. However, the stopping power below 10 keV has become important for the application to three fields of radiobiology, solid state physics and nuclear fusion research. For this reason, the theory, experimental results and problems concerning stopping power, mean free path and flight range in these several years are introduced. From some experimental varification and the data on these basic quantities of the electrons above 10 keV so far, it has been found that a series of the calculated results by the free electron gas model and the statistical electron gas model are valid for application instead of the experimental data of poor systematicness. (Wakatsuki, Y.)