Abstract: A reflection prevention board of a charged particle beam irradiation apparatus of the present invention comprises a laminate sheet having a plurality of thin films and a plurality of microholes through the laminate sheet. According to the present invention the reflection prevention board can be manufactured at a lower cost, the reason being that it is easier to form microholes in the thin films and then laminate these thin films in an aligned relation than to drill holes through a thicker sheet. By doing so it is possible to achieve a better yield. Further, much deeper microholes, which might not otherwise be achieved on a thick sheet, can be formed by using more thin films and a reflection prevention effect can be improved by doing so.

Abstract: A charged beam applying apparatus comprises a column at least having a charged beam generation section and optical system for controlling the charged beam and a chamber for holding a specimen in place which is exposed with the charged beam. At least one inner portion of the column is formed of a specific material whose an atomic number is equal or less than 22. When a contamination is cleaned off in the column through the utilization of an oxidation effect, an oxide film is sometimes formed inside the column. The electric charging of the oxide film causes a beam control error. The specific material such as the metal of the atomic number causes very much less such error. This is because such specific material involves less emission of secondary electrons and less electric charging in the oxide film formed.

Abstract: A charged beam apparatus comprises a source tank provided outside the column and containing a plasma source, a plasma generating apparatus for generating plasma from a plasma source supplied from the source tank, gate valves and an exhausting pump for introducing plasma generated by the plasma generating apparatus into the column and for exhausting the plasma therefrom, and an O-ring for restricting a passage of plasma in the column such that those portions of cleaning portions to be cleaned to which internal contaminants stick are mainly exposed to plasma. Therefore, it is possible to generation of an oxide film, a fluoride film, or the likes which cause drifting can be restricted.

Abstract: The core of a nuclear reactor is constituted by two sorts of fuel assemblies: first fuel assemblies each of which contains both fissile material and gadolinea and second fuel assemblies each of which contains only the fissile material. The ratio of the number of the first fuel assemblies to that of the second fuel assemblies are selected to be 1:3. The enrichment of the fissile material is larger at the upper part of the reactor core than at the lower part of the same. The fuel assembly containing both of the fissile material and the gadolinea includes first fuel rods each of which contain both the fissile material and the gadolinea, and second fuel rods which contains only the fissile material. The number of the first fuel rods and the concentration of gadolinea are substantially in proportion to the power density at positions in the reactor core where the fuel assembly is placed.

Abstract: A fuel assembly suitable for use in boiling water reactor. The fuel assembly has a specific pattern of distribution of enrichment, so that the upper region of the assembly has a larger infinite multiplication factor than that of the lower region. In an example, the distribution of enrichment is such that the upper region has a mean enrichment larger than that of the lower region, while, in another example, the mean enrichment is maintained constant over the length of the assembly but the difference of enrichments between the central and peripheral portions of a plane normal to the axis of the assembly is made smaller at the upper region than at the lower region.