Electric lamp and discharge devices – Photosensitive – Having phosphor screen
Utility Patent
1998-07-17
2001-01-02
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Photosensitive
Having phosphor screen
C313S525000, C313S527000, C313S541000, C250S2140VT
Utility Patent
active
06169360
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an X-ray image intensifier and its production method for manufacturing thereof, and more particularly to a substrate on which an input screen is formed and its production method.
BACKGROUND OF THE INVENTION
An X-ray image intensifier, which is an electron tube for converting an X-ray image into a visible image or an electrical image signal, is being used in various fields such as medical and industry. As shown in
FIG. 20
, such an X-ray image intensifier comprises a spherical substrate
12
which forms a part of a vacuum envelope
11
and also serves as an input window, an input screen
13
which converts an X-ray image formed on the inner face of the substrate
12
into an electron image, a plurality of focusing electrodes
14
a,
14
b,
14
c
and anode
14
d
which configure an electron lens, and an output screen
15
which converts the electron image into a visible image.
The substrate
12
is generally aluminum or aluminum alloy (simply called aluminum) which has good X-ray permeability. The input screen
13
includes a layer of optically reflective layer
16
deposited on the substrate, a phosphor layer
17
which is formed of an aggregate of columnar crystals deposited on the layer of optically reflective layer
16
, an optically transparent intermediate layer
18
adhered onto the phosphor layer
17
, and a photocathode
19
.
An X-ray image externally entered through the substrate
12
is emitted and converted into an electron image by the input screen
13
, focused by an electron lens system, and converted into a visible image or an electric image signal by an output screen
15
. The output visible image is transmitted to an X-ray TV camera or spot camera through the optical lens (not shown) positioned behind it and shown on a CRT monitor or the like by electrical image processing.
Meanwhile, in the recent X-ray image photography technology, higher resolution and brightness uniformity is demanded to be improved. Specifically, in this field, an image contrast is enhanced by the image integration processing or the like, and for example, defects on an output image due to minute scratches, stains or many etch pits or minute holes on the substrate surface due to etching are enhanced undesirably, and image noises which cannot be disregarded are caused.
According to the study made by the inventors, main causes of such image noises are assumed to be minute irregularities such as rolling lines caused when the substrate material is rolled and etch pits caused by etching for cleaning. Specifically, the surface of the substrate immediately be fore the input screen is formed was observed through a microscope to find irregularities having parallel directivity seemingly due to the rolling lines caused when the substrate material was rolled, countless irregular minute irregularities that the substrate material has originally and countless irregularities
12
a
such as etch pits as schematically shown in FIG.
21
.
And, the conventional substrate surface having minute irregularities and the input screen formed on it has a part of light emitted on the phosphor layer
17
excited by X-rays entered sent to the substrate
12
and reflected in irregular directions as indicated by an arrow Y due to the countless irregularities
12
a
on the substrate surface or the surface of the layer of optically reflective layer (not illustrated).
The reflected light has its part returned into the same columnar crystal P where the light is emitted from, but another part enters another columnar crystal P next to the former columnar crystal P in the horizontal direction. Therefore, a possibility that the reflected light returns into the same columnar crystal is decreased as the surface of the substrate gets rougher, and resolution of an output image is degraded, and image noises are produced. And, if many etch pits are formed on the substrate surface by etching, very small pits are covered with the layer of optically reflective layer, while relatively large pits appear as spotted noises on the output image, and the image quality is degraded.
The formation of the phosphor layer of the columnar crystals by forming it on the irregularities on the substrate surface or the polished substrate surface as a mirror is disclosed in, for example, Japanese Patent Publication No. Sho 52-20818, its corresponding U.S. Pat. No. 3,473,066, U.S. Pat. No. 3,852,133, Japanese Patent Laid-Open Publication No. Sho 55-150535, Japanese Patent Laid-Open Publication No. Sho 57-82940, Japanese Patent Laid-Open Publication No. Hei 4-154032, and WO-94/22161.
But, most of them relate to a technology of forming regular pits and projections on the substrate surface and growing phosphor crystals depending on the pits and projections. They also relate to a technology of enhancing resolution by making the substrate surface flat and a mirror face to suppress the irregular reflection of the emitted light thereon. But, when the substrate surface is flat and mirror-like, the resolution is improved, but the adhesiveness of the input screen tends to be insufficient. Therefore, among the technologies described above, those practically used are not many.
The present invention was achieved in view of the circumstances described above and aims to provide an X-ray image intensifier which provides an input screen with sufficient adhesiveness, output image noises decreased and good resolution, and its production method.
REFERENCES:
patent: 4847482 (1989-07-01), Kubo
patent: 5045682 (1991-09-01), Ono et al.
Noji Takashi
Sekijima Yoshinobu
Tanno Kazutoshi
Yamada Hitoshi
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Ashok
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