Victoreen Model 6306 High Efficiency GM (1950s)
The Victoreen Model 6306 GM tube "is designed for portable survey instruments, area monitoring devices, and precision laboratory measuring equipment." It is very similar to the Victoreen 1B85 tube except that it is primarily intended for gamma ray measurements. According to the Victoreen specification sheet "it is interchangeable mechanically and electrically with the 1B85 counter tube" but that "it is not recommended as a replacement for 1B85 for counting betas."
To give the tube a high efficiency for gamma ray detection, there is a plating of bismuth (105 mg/cm²) on the inside of the wall. The high atomic number of the bismuth (which serves as the tube's cathode) increases the probability of gamma ray interactions. For 50 keV gamma rays, the 6306 has about twice the sensitivity of the 1B85. For 200 keV gammas it has ten times the sensitivity.
The 6306 tube is also lined with a copper screen to provide mechanical strength. Unlike the 1B85, the 6306 can be handled without a constant fear that it is about to collapse.
The photo to the right shows three 6306 tubes ganged together in an Atomic Research Corporation survey meter. Quoting the manufacturer's literature: "It is ideally suited for parallel operation requiring no decoupling networks. When used in clusters, these tubes compare favorable in cost and performance with scintillation detectors."
Size: 4 1/8" long, 51/64" diameter
Active length: 2 3/4"
Wall: Aluminum, 30 mg/cm²
Operating voltage: 850 - 950 volts
Gas: Argon plus organic quench
- Nucleonics, November 1956, page 113.
- Nucleonics, June 1953, page 95.
- Victoreen Data sheet for 6306.