Photomultiplier tube tightly arranged with substantially no space between adjacent tubes

A radiation detector comprising:

• a scintillator for emitting fluorescent light in response to radiation generated from an object of analysis;
• a plurality of photomultiplier tubes for outputting electric charges based on fluorescent light emitted from the scintillator, and a position calculating section for performing calculations on the electric charges output from the plurality of photomultiplier tubes and outputting positioning signals of radiation issued from the object of analysis,
• wherein each of the plurality of the photomultiplier tubes comprises:
• a faceplate disposed in opposition to the scintillator;
• a photocathode for emitting electrons in response to light incident on the faceplate;
• an airtight vessel;
• an electron multiplying section, disposed inside the airtight vessel, for multiplying the electrons emitted from the photocathode;
• and
• an anode for outputting an output signal based on the electrons multiplied by the electron multiplying section,
• wherein the airtight vessel comprises:
• a metal stem plate for fixedly supporting the electron multiplying section and the anode with stem pins;
• and
• a metal side tube with the stem plate fixed on one open end, and enclosing the electron multiplying section and the anode;
• wherein the faceplate is fixed on the other open end of the metal side tube,
• and wherein the radiation detector includes a photomultiplier tube unit in which a plurality of airtight vessels are juxtaposed, and outer surfaces of the plurality of airtight vessels are flat and in facial contact with one another, each outer surface being perpendicular in entirety to the corresponding photocathode.