Electron multiplier including dynode unit, insulating plates, and columns

An electron multiplier comprising:

• a dynode unit, having a plurality of dynodes positioned in a mutually-insulated, layered state in multiple stages and disposed in a vacuum container;
• an anode housed inside the vacuum container;
• a plurality of insulating plates, insulating the respective dynodes from each other;
• and
• columns, erected from a stem plate, making up the vacuum container, so as to fit or engage with the respective dynodes, anode, and the respective insulating plates,
• wherein the respective dynodes and the respective insulating plates are overlapped alternating in the state of being fitted or engaged with the columns and the respective dynodes and the respective insulating plates are supported integrally on the columns by means of arresting members being fixed to the tip portions of the columns,
• wherein a rear edge of each respective column is fixed to the stem plate and the arresting members are fixed to a front edge of each respective column,
• wherein an insulating part is provided so as to surround each respective column in the area near the rear edge so that each dynode, anode, and insulating plate are stacked on the insulating part,
• wherein the stem plate includes a metallic plate-shaped material structurally configured into a concave shape, the concave shape being filled-in with an insulating sealing member so that each respective column is erected through the stem plate and is embedded in the insulating sealing member, and
• wherein the insulating part, which is configured so as to surround each respective column, is disposed so as to be in direct contact with a top surface of the stem plate.