Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2002-11-08
2004-12-28
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S207000, C313S1030CM
Reexamination Certificate
active
06835922
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a photomultiplier tube for detecting weak light incident on a faceplate by multiplying electrons emitted on the faceplate, and a method for manufacturing the photomultiplier tube.
BACKGROUND ART
Japanese patent Kokai publication No. Hei 5-290793 discloses a conventional photomultiplier tube wherein a hermetically sealed vessel accommodates an electron multiplier. Referring to
FIG. 18
, a flange
101
is formed over the entire upper end of a metal side tube
100
. A lower end face
111
a
of the flange
101
contacts an upper face
102
a
of a faceplate
102
. The side tube
100
and an upper face
102
a
of the faceplate
102
are then crimped and welded. Therefore, the flange
101
ensured that the vessel is hermetically sealed.
Heating the side tube
100
is required to weld the side tube to the faceplate. If the side tube
100
has a rectangular section, the amount of heat generated on each of the four corners in the flange
101
is greater than that of the portions other than the corners of the flange
101
. As a result, when the flange
101
is fixed to the faceplate
102
, a problem may arise that the fixed conditions on the corners are different from those of the portions other than the corners. Accordingly, the problem may affect throughput of manufacturing photomultiplier tubes. Additionally, deformation of the flanges due to heat may result in instability of the hermetic property of the vessel.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a photomultiplier tube and a manufacturing method thereof in which the method provides improved throughput, and integration of the side tube and the faceplate are ensured to obtain enhanced hermetic sealing of the vessel.
The present invention features a photomultiplier tube which has a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. The hermetically sealed vessel includes: a stem plate having stem pins for fixing the electron multiplier and the anode thereon; a metal side tube enclosing the electron multiplier and the anode, and having one open end to which the stem plate is fixed; and the faceplate fixed to another open end of the side tube, the faceplate being made of glass. The side tube has a polygonal shape defined by a plurality of plates, each of the plurality of plates having a rolled-up upper end, and the side tube is fused to the faceplate in such a manner that the upper end of each side is embedded in a photocathode side of the faceplate.
In the above photomultiplier tube, the rolled-up edges of the plurality of plates are joined so that the joined plates have a polygonal shape. Each corner, that is, the joint of the plates, is raised more than the other portions. As a result, the upper end of the side tube is more deeply embedded in the faceplate, which contributes to an improved joint condition between the side tube and the faceplate. In addition, the fusion between the side tube and the faceplate is ensured, so that the hermetic seal at the joint portion between the side tube and the faceplate is improved. The throughput of manufacturing the photomultiplier tube is improved.
In the photomultiplier according to present invention, the side tube preferably has an edge portion on the upper end, the edge portion being embedded in a photocathode side of the faceplate. The edge portion provided in the side tube is embedded perpendicularly to the glass faceplate, which contributes to conformability between the side tube and the faceplate and reliability of tight hermetic seal. The edge portion extends upright from the side tube rather than laterally from the side tube like a flange. When the edge portion is embedded as closely as possible to the side face of the faceplate, the effective surface area of the faceplate is increased to nearly 100%. The dead area of the faceplate can be decreased to as nearly 0 as possible.
A tip end of the edge portion of the photemultiplier tube preferably extends straight. This structure enables the edge portion of the side tube to pierce the faceplate. Furthermore, the edge portion is on a line extending from the side tube, which promotes enlargement of the effective sensitive area of the faceplate.
According to present invention, a tip end of the edge portion of the photomultiplier tube may be curved in either one of an interior and an exterior of the side tube. This structure increases a surface area of the edge portion embedded in the faceplate, contributing to improved hermetic seal of the joint between the side tube and the faceplate.
The edge portion of the photomultiplier tube preferably has a knife-edged tip end. This structure enables the edge portion of the side tube to pierce into the faceplate. Therefore, assembly operation and reliability are improved when the glass faceplate is fused to the side tube.
In the photomultiplier tube according to the present invention, it is preferable that an inner side wall at the lower end of the side tube is in contact with an end face of the metal stem plate, then the metal side tube and the metal stem plate are welded together. If this structure is adopted, the side tube and the faceplate are fused together, with an inner side wall at the lower end of the side tube being in contact with an edge face of the stem plate. Therefore, a projection such as a flange is eliminated at the lower end of the photomultiplier tube. Accordingly, it is possible to reduce the external dimensions of the photomultiplier tube, though the above structure of the photomultiplier tube and the side tube may be improper for resistance-welding. When several photomultiplier tubes are arranged, it is possible to place the side tubes closely to each other.
The present invention provides a photomultiplier tube having: a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. The hermetically sealed vessel includes: a stem plate having stem pins for fixing the electron multiplier and the anode thereon; a metal side tube having open ends and enclosing the electron multiplier and the anode, the stem plate being fixed to one of the open ends; and the faceplate fused to the other open end of the side tube, the faceplate being made of glass. The side tube has a cylinder having a polygonal section, the side tube having a plurality of corners, an end face on each of the plurality of corners protrudes beyond an end face of the side tube other than the end faces on the plurality of corners, the faceplate is fused to the other open end so that the other open end is embedded in the photocathode side of the faceplate.
The end face corresponding to the corner at the open end of the side tube facing the faceplate is at a higher level than that of the end face other than the corner. At first, the faceplate is supported by the protruding end face on the corner. Then, melting of the faceplate is started from the supporting position, so that the positional relationship between the side tube and the faceplate is ensured at an early stage of the fusion. Accordingly, the shape of the side tube is readily maintained even during heating.
The present invention features a method for manufacturing a photomultiplier tube having: a photocathode for emitting electrons in response to light incident on a faceplate; an electron multiplier in an hermetically sealed vessel for multiplying electrons emitted from the photocathode; and an anode for generating an output signal based on electrons multiplied by the electron multiplier. The photomultiplier tube includes a side tube having a polygonal section with a plurality of plates, each of the plurality
Kyushima Hiroyuki
Masuda Yuji
Shimoi Hideki
Allen Stephone B.
Hamamatsu Photonics K.K.
Oliff & Berridg,e PLC
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