Amperex Model 120NB End Window GM (1950s, 1960s)

Amperex 120NB End Window GM Detector

This rather large end window GM tube was manufactured by Amperex Electronic Corporation of Brooklyn New York. Its main purpose would have been to count beta particles—the window is sufficiently thick that it would not respond to alpha particles. I believe that the N in the model number refers to the use of a neon fill gas and that the B refers to the four pin base.

Size: 5.75” long and 2.312” diameter

Window: 1.906" effective diameter, 5.6 mg/cm²

Operating voltage: 900 volts

Dead time: ca. 300 usec

Cathode: Stainless steel coated on outside with plastic.

Gas: Neon, halogen quenched

Base: Four prong


  • Atomic Energy Commission Radiation Instrument Catalog, Date July 1, 1950, page BG-1A11A.
  • Amperex Nuclear Products catalog of radiation tubes, 1981.
Amperex 120NB End Window GM Detector