Ultraviolet detector

Abstract

An ultraviolet detector comprises a metal tubular member which hermetically encloses an anode and a cathode therein and is filled with a discharged gas introduced therein from a metal exhaust tube. After the anode and the cathode are enclosed within the tubular member, the ultraviolet detector can be made without being subjected to any glass fusing process. Accordingly, the inside of the sealed vessel V1 can be prevented from being contaminated with fluorine, whereby the ultraviolet detector with stable characteristics can be provided.

Description

BACKGROUND OF THE INVENTION1. Field of the InventionThe present invention relates to an ultraviolet detector which detects ultraviolet radiation incident thereon by converting them into an electric signal.2. Related Background ArtAn example of conventional ultraviolet detectors is disclosed in Japanese Utility model Publication No. 49-17184. This publication discloses an ultraviolet detector in which an anode and a cathode are disposed within a sealed vessel constituted by a glass envelope and a glass bottom plate welded to the bottom portion of the glass envelope.Though the conventional ultraviolet detector mentioned above is an excellent detector which has a long life and can stably detect ultraviolet radiation, its characteristics may not be sufficient. Specifically, when used for a long period of time, its characteristics may deteriorate over time, thus lacking in stability.SUMMARY OF THE INVENTIONIn order to overcome such shortcomings, various studies have conventionally been m...

AI Technical Summary

Benefits of technology

In order to overcome such shortcomings, various studies have conventionally been made. The inventors have elucidated that these shortcomings result from the glass material used as a window material for the ultraviolet detector. Typical glass materials which are transparent to ultraviolet radiation contain fluorine. Upon welding of the envelope and bottom plate of the ultraviolet detector, fluorine contained in the glass material evaporated from the glass material and adsorbed onto the surfaces of the anode and cathode, the inner surface of the sealed vessel, and the like. Normal operation of the detector and the aging process in fabrication both include the gas discharge between the electrodes. Electrons and ions generated by the gas discharge impinge onto the surfaces of the anode and cathode respectively. It causes the desorption of fluorine adsorbed on the surface of these electrodes. The fluorine containments on the other sites in the vessel can also be desorbed by means of the heat which arises in the aging processes of the detector fabrication and even in the normal operation condition of the detector. The desorbed fluorine alters the ionization property of the discharged gas filled in the vessel. This alternation commonly results in the lowering of the breakdown voltage and that leads to occasional and continuous false discharges and unwanted increase of the sensitivity. These effects considerably degrade the stability and the reliability of the detector.

In such a configuration, since the tubular member is made of a metal material blocking ultraviolet radiation, incident ultraviolet radiation are introduced through the window member made of an ultraviolet-transparent material toward the anode and cathode of the detector, whereby the detector exhibits a high directivity. Further, since the tubular member is made of a metal material, even when this tubular member is connected to the metal portion of the stem by pressure or welding, impurities such as fluorine do not attach to the sealed vessel, anode, and cathode. Accordingly, the ultraviolet detector in accordance with the present invention is prevented from being affected by fluorine or the like, whereby the break down voltage of the detector can be held stably.

And more, the cathode of the present invention is secured to the tubular member or the metal portion of the stem without a stem pin. So it is easy to manufacture the ultraviolet detector having discharging gap with a high precision.

Such configuration aids in facilitating manufacture of high accurate ultraviolet detector.

Problems solved by technology

This alternation commonly results in the lowering of the breakdown voltage and that leads to occasional and continuous false discharges and unwanted increase of the sensitivity.

These effects considerably degrade the stability and the reliability of the detector.

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