JPS6151736A - X-ray image intensifier - Google Patents

Abstract

PURPOSE:To improve a resolution property and a contrast property by so constructing an input phosphor screen as to have a large number of CsI crystals formed in a drill shape widening toward the direction of a photoelectric surface. CONSTITUTION:A substrate 1 is provided with a large number of widning and about trapezoidally shaped projections 11 by a technique of lithography or the like while CsI is vacuum-evporated on the tip side of said projections so as to form a large number CsI crystals 21 in a drill shape widening toward the direction of a photoelectric surface 3. On said input phosphor screen 2, the photoelectric surface 3 consisting of a transparent conductive film 31 and a photoelectric film 32 is provided. Thereby, when scintillation is generated in a certain crystal, the amount of light totally reflecting on the side toward the photoelectric surface 3 is increased while reducing cross talk for improving a resolution property. Further, when scintillation is generated in one CsI crystal, the amount of light reaching the photoelectric surface only through inside said CsI crystal is increased so as to improve efficiency of detecting X-ray electrons while improving a contrast property.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an X-ray image intensifier that outputs an X-ray image as an optical image while multiplying its brightness, and particularly relates to improving its input phosphor screen. .

(b) Prior art X-ray image intensifiers usually have a structure as shown in FIG. An input phosphor screen 2, which is an aggregate of fiber-shaped (needle-shaped) CsI crystals 22, is formed on the substrate 1, and a photocathode 3 consisting of a transparent conductive film 31 and a photoelectric film 32 is formed thereon ( (See FIG. 4), the assembly of the substrate 1, the focusing electrode 4, the accelerating electrode 5, and the output phosphor screen 6 are enclosed in a vacuum envelope 7.

The X-rays that have passed through the object pass through the vacuum envelope 7 and the substrate 1, and then pass through one crystal 22 of the input phosphor screen 2.
It enters the membrane, causes interaction (scintillation), and emits light. This scintillation light is converted into electrons at the photocathode 3 , and these electrons are focused by a focusing electrode 4 and accelerated by an accelerating electrode 5 to form an image on an output phosphor screen 6 . In this way, an optical image appears on the output phosphor screen 6.

By the way, the input phosphor screen 2 has C5I on the substrate 1 with the number 11
After vapor deposition to a thickness of 00p, cracks are formed therein to form a large number of fiber-like (needle-like) crystals 22 with a diameter of several ILm. If light is emitted in the same direction at the point 10 in a fiber crystal 22 as shown in FIG. 4, the light will be
There are those that repeatedly reflect within the fiber-like crystal 22 that emitted light and reach the photocathode 3, and those that escape from the crystal 22 and enter an adjacent or nearby crystal 22 before reaching the photocathode 3. Divided. That is, as shown in FIG. 5, if the incident angle θ1 is larger than the critical angle i, no light will be emitted from the crystal 22 due to total reflection, but if the incident angle θ2 is small, the light will be emitted from the crystal 22. is expressed as 5ini=ni/nz when the boundary surface is a plane (where nl and n2 are refractive indexes, and if light in a medium with a refractive index nl is refracted at the interface with the medium where the refraction in≧ is smaller than nl) ).

The light that goes out of the crystal and reaches the photocathode via other crystals in this way is called crosstalk, and the presence of this crosstalk is a factor in the deterioration of resolution characteristics and contrast characteristics.

(c) Purpose This invention improves crosstalk by allowing the light to reach the photocathode without leaving the crystal as much as possible when scintillation occurs in a certain CsI crystal due to the incidence of X-rays. An object of the present invention is to provide an X-ray image intensifier with improved resolution characteristics and contrast characteristics.

(D) Structure The input phosphor screen of the X-ray image intensifier according to the present invention has a structure including a large number of CsI crystals formed in a cone-like shape that widens toward the photocathode.

(E) Example As shown in FIG.
1 is formed into a cone-like shape that widens toward the photocathode 3 . A large number of such pyramidal crystals 21
An input phosphor screen 2 is formed. The photocathode 3 consisting of a transparent conductor 11931 and a photoelectric film 32 is provided on the input phosphor screen 2, and the other configurations are the same as those of a normal X-ray image intensifier.

In addition, such a large number of cone-shaped CsI crystals 21 that widen toward the photocathode 3 are obtained by providing a large number of generally trapezoidal protrusions 11 that widen toward the end on the substrate l using a technique such as linography, and then attaching the tips of these protrusions to It can be formed by depositing CsI on the side.

Since the large number of CsI crystals 21 constituting the input phosphor screen 2 are in the shape of a cone that widens towards the photocathode 3, each crystal 21 has a side surface as shown in FIG. The amount of light that is totally reflected and directed toward the photocathode 3 can be increased, and crosstalk can be improved. In other words, it is cone-shaped and its sides are inclined (the angle of inclination is θO).
Therefore, the apparent critical angle i can be made smaller (the apparent critical angle is i-〇〇) compared to the case where it is not tilted (see Figure 5). This is because the light can be totally reflected within the crystal 21 and reach the photocathode 3 as shown in FIG.

(F) Effect According to the present invention, a large number of CsIs constituting the input phosphor screen
Because the crystals are formed in the shape of a cone that widens toward the photocathode, when scintillation occurs in one crystal, the amount of light that penetrates from that crystal to the neighboring crystal is reduced, reducing crosstalk. resolution characteristics are improved. Furthermore, when scintillation occurs in one CsI crystal, the amount of light that passes only within that CsI crystal and reaches the photocathode increases, so that the x&l quantum detection efficiency is improved and the contrast characteristics are improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an input phosphor screen according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the reflection of light in the crystal of FIG. 1, and FIG. 3 is an X-ray image input. FIG. 4 is a schematic cross-sectional view of a tensifier, FIG. 4 is a cross-sectional view showing a conventional input phosphor screen, and FIG. 5 is a diagram for explaining the reflection of light in the crystal of FIG. 4. 1... Board 2... Input fluorescent screen 21.
...Finding cone-shaped crystal 22...Fiber-like crystal 3...Photocathode 31...
Transparent conductive film 32...Photoelectric film 4...Focusing electrode
5... Accelerating electrode 6... Output fluorescent screen
7...Vacuum envelope 10...1 light emitting point each, total of 2 points - ray area

Claims (1)

[Claims] (1) X-rays consisting of an input phosphor screen that emits light when X-rays are incident on it, a photocathode that converts this light into electrons, an output phosphor screen where an optical image appears due to the electrons, and a vacuum envelope that surrounds them. In the image intensifier, the input phosphor screen has a structure having a large number of CsI crystals formed in a cone-like shape that widens toward the photocathode.・Intensifier.