Electron tube

Details Electron tube Electron tube

1998-12-09

2001-03-06

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Photosensitive

Photocathode

C313S544000, C313S532000, C250S398000, C250S207000, C250S2140VT

Reexamination Certificate

active

06198221

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electron tube utilized as a photodetector for quantitatively measuring weak light. In particular, the present invention relates to an electron tube equipped with a sensing device having an electron entrance surface such as a semiconductor device for multiplying and outputting electrons emitted from a photocathode.
2. Related Background Art
There have conventionally been known electron tubes in which electrons emitted from a photocathode are accelerated and converged by an electron lens and then are made incident on a semiconductor device to yield a high gain. Such electron tubes are disclosed, for example, in U.S. Pat. No. 5,120,949, U.S. Pat. No. 5,374,826, and S. Base et al., “Test Results of the First Proximity Focused Hybrid Photodiode Detector Prototypes,”
Nuclear Instruments and Methods in Physics Research,
A330 (1993), 93-99. In particular, the above-mentioned Base reference discloses an electron tube such as that shown in FIG.
1
. This electron tube has an electrical insulating bulb
102
which secures electrical insulation between an anode
100
and a cathode electrode
101
. The inner diameter of the cathode electrode
101
is made greater than that of the bulb
102
, whereby a photocathode
103
has a large area, allowing a semiconductor device
104
to have an increased effective area (e.g., 100 mm
2
). Accordingly, it can be seen that the electron tube shown in
FIG. 1
has a large size. The cathode electrode
101
employed in this electron tube is constituted by two pieces of cylindrical metal members
101
a
and
101
b
having inner diameters different from each other disposed concentrically with a gap therebetween.
SUMMARY OF THE INVENTION
Having studied the above-mentioned prior art, the inventors have found the following problems to be overcome. The cathode electrode
101
of the electron tube shown in
FIG. 1
can be configured into various sizes and forms as two pieces of cylindrical metal members
101
a
and
101
b
are combined together. Though it is suitable for a large electron tube since a gap must be formed between these metal members
101
a
and
101
b,
such a gap is hard to secure in a small electron tube (with a diameter of about 10 mm, for example). Also, in order to assemble such a cathode electrode
101
, each of two planar sheets must be pressed and then sealed by welding or the like into a cylindrical form, thereby yielding a low efficiency in the assembling operation.
It is thus an object of the present invention to provide an electron tube which can reduce its size and has a structure for improving the workability in its assembling process.
In order to achieve this object, the electron tube according to the present invention comprises, at least, a face plate on which a photocathode for emitting a photoelectron in response to incident light is disposed; an electron entrance surface (corresponding to the electron entrance surface of an avalanche photodiode or the like) on which the photoelectron emitted from the photocathode is incident, the electron entrance surface being arranged so as to face the photocathode; a cathode electrode positioned between the face plate and the electron entrance surface; and a bonding member, provided between the face plate and the cathode electrode, for bonding the face plate and the cathode electrode together.
The electron tube according to the present invention further comprises a body. The body can be selected from at least one of a pipe type having a first opening and a second opening opposing the first opening, and an envelope type having one opening and a bottom portion. The electron tube having the pipe type body preferably has a stem, and wherein the cathode electrode is arranged on the first opening side of the pipe type body and the stem is arranged on the second opening side of the pipe type body. The stem functions to define a distance between the photocathode and the electron entrance surface facing the photocathode. On the other hand, in the envelope type body, the cathode electrode is arranged on the opening of the envelope type body, and the bottom portion functions as the above-mentioned stem.
In particular, the bonding member is made of a metal material selected from the group consisting of In, Au, Pb, alloys containing In, and alloys containing Pb. In the electron tube according to the present invention, in order to allow its size to decrease, after the step for forming the photocathode (heating to about 300° C.), the cathode electrode and the body are bonded together in an atmosphere at a temperature much lower than that in the photocathode-forming step. Accordingly, as the material for the bonding member, materials which can sufficiently deform at a pressure of about 100 kg in the atmosphere at room temperature are preferable, whereas metals such as aluminum are unfavorable.
The cathode electrode has a through-hole for transmitting therethrough the photoelectron from the photocathode toward the electron entrance surface. In the case of selecting the pipe type body, the electron tube comprises a welded electrode arranged at the second opening side of said body and positioned between the body and the stem. This welded electrode also has a through-hole for transmitting therethrough the photoelectron transmitted through the through-hole of the cathode electrode toward the electron entrance surface.
The electron tube according to the present invention may further comprise an anode having a through-hole for transmitting therethrough the photoelectron transmitted through the cathode electrode (first embodiment). This anode is supported by the welded electrode such that at least part of the anode is positioned between the cathode electrode and the electron entrance surface, thereby constituting an electron lens together with the cathode. In the first embodiment, it is preferred that the through-hole of the anode has an area equal to or smaller than the electron entrance surface. It is due to the fact that, when a photoelectron from the photocathode reaches the surroundings of the electron entrance surface, the device is deteriorated or charged. Alternatively, a part of the welded electrode may be configured to function as the anode (second embodiment). Also in the second embodiment, it is preferred that the through-hole of the anode has an area equal to or smaller than the electron entrance surface.
In addition, the welded electrode comprises a portion to be resistance-welded to the stem. The stem has a mounter section, projecting toward the photocathode, for holding a semiconductor device.
In the electron tube according to the present invention, light incident on the face plate from the outside is converted into electrons by the photocathode. While the orbit of the electrons is converged by an electron lens effect formed by the cathode electrode and anode cooperating together, the electrons reach the electron entrance surface of the semiconductor device or the like. Here, the cathode electrode has a cylindrical form and can be made easily by any of various integral-molding methods such as press molding, injection molding, or cutting. Also, a small cathode electrode can easily be materialized when required, allowing the electrode to further decrease its size. Since each of the cathode electrode, body, and welded electrode is formed like a ring, they can easily be mounted on each other concentrically. Accordingly, in order to form a vacuum case, the operation for assembling the case is facilitated. As the electron tube is made smaller, the present invention can satisfy a strong demand in the fields of high energy and medical instruments for using 1,000 to 10,000 pieces of electron tubes arranged in a limited space. Also, when a ring-shaped member made of indium is disposed between the cathode electrode and face plate in the case, and the face plate (provided with a photocathode beforehand) and the cathode electrode are pressed against each other while a high pressure of about 100 kg is applied thereto in a v

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