| 摘要 |
PROBLEM TO BE SOLVED: To reduce the danger of a beam emitting window being damaged by collision of back scattering electrons by holding the beam emitting window in a cathode potential, and electrically insulating it to a vacuum casing. SOLUTION: The position of a beam emitting window 23 is selected so that the angleβbetween the central beam ZS of an effective X-ray bundle an the normal N of a colliding surface 22 is substantially equal to an angleα. Thus, at least a substantially circular focal point more advantage for imaging of high quality is generated in the direction of the beam ZS. The window 23 is formed of a proper conductive material, and connected to a vacuum casing 1 through an insulating material 20. A cathode potential is added to the window 23, whereby back scattering electrons moved toward the window 23 are eliminated, and energy-selectively scattered. When the window 23 is circular, the electrons are scattered rotation-symmetrically. Thus, the electrons are not collided to the window 23, but collided to the area surrounding the window 23.
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