Patent ID: 8796925

Claim:
A discharge tube comprising: a first electrode, a second electrode, and a third electrode arranged in parallel; and an airtight outer enclosure including a first tubular body made of an insulating material and sandwiched between the first electrode and the second electrode, and a second tubular body made of an insulating material and sandwiched between the second electrode and the third electrode, a through-hole being formed in the second electrode and allowing internal spaces of the first tubular body and the second tubular body to communicate with each other, on the first electrode and the third electrode, discharge electrode portions being formed which protrude toward a center of the airtight outer enclosure and are disposed opposite to each other with a predetermined discharge gap provided in between, and a discharge gas being filled in the airtight outer enclosure, wherein on an end surface of the discharge electrode portion a film is formed containing cesium nitrate, rubidium nitrate, magnesium oxide and glass.