Photomultiplier tube

A photomultiplier tube having a faceplate (3), a photocathode (3a) for emitting electrons in response to light incident on the faceplate (3), an electron multiplying section (9), disposed inside an airtight vessel (5), for multiplying the electrons emitted from the photocathode (3a), and an anode (12) for outputting an output signal based on the electrons multiplied by the electron multiplying section (9), characterized in that the airtight vessel (5) is formed by:

• a stem plate (4) for fixedly supporting the electron multiplying section (9) and the anode (12) with stem pins (10);
• a side tube (2) with the stem plate (4) fixed on one open end, the side tube (2) being formed of metal and enclosing the electron multiplying section (9) and the anode (12);
• and
• the faceplate (3) fixed on the other open end of the side tube (2), and
• that an inner surface of a lower portion of the side tube (2) is in contact with an outer edge of the stem plate (4) so that the lower portion of the side tube does not extend beyond other portions of the side tube, at least a portion of the stem plate (4) contacting the inner surface of the lower portion of the side tube (2) is formed of metal, the portion thereof including the outer edge of the stem plate (4), and the side tube (2) is welded to the stem plate (4).