PROBLEM TO BE SOLVED: To increase a withstand voltage characteristic of a radiation generating unit 10 in which a radiation generating tube 20 which generates radiation by applying voltage between a cathode 22 and an anode 23 provided at both ends of a tubular member 26 is stored within a storage container 12 filled with an insulative substance 18.SOLUTION: The tubular member 26 has an annular protrusion 27 on an outer periphery thereof, and when a relative dielectric constant ε2 of the insulative substance 18 is greater than a relative dielectric constant ε1 of the tubular member 26, the distance between the cathode 22 and the anode 23 is L, the shortest distance between the cathode 22 or the anode 23 and the protrusion 27 is d, the rise angle of the protrusion 27 from the surface of the tubular member 26 at the position with the distance d is θ, the width of the protrusion 27 is W, and the height of the protrusion 27 is H, the relations expressed by the following expression (1) is satisfied. 1>d/L≥0.001×ln(H/W)-0.001×ln[cos(θ)]-0.004×(H/W)×cos(θ)+0.004 ...(1)COPYRIGHT: (C)2014,JPO&INPIT【課題】管状部材26の両端に設けられた陰極22と陽極23に電圧を印加して放射線を発生させる放射線発生管20を絶縁性物質18で満たされた収納容器20の内部に収容した放射線発生ユニット10の耐電圧特性を向上させる。【解決手段】管状部材26は外周に環状の凸部27を有し、管状部材26の比誘電率をε1より絶縁性物質18比誘電率をε2が大きく、陰極22と陽極23との距離をL、陰極22又は陽極23と凸部27との最短距離をd、距離dの位置での管状部材26の表面からの凸部27の立ち上がり角度をθ、凸部27の幅をW、凸部27の高さをHとした時に、下記式(1)の関係を満たすようにする。1>d/L≧0.001×ln(H/W)-0.001×ln〔cos(θ)〕-0.004×(H/W)×cos(θ)+0.004 ・・・(1)【選択図】図1
