1B124 — Metal Counter Thyrode Tube

The 1B124 is a sturdily constructed metal Geiger-Mueller counter tube, designated as a Thyrode. It is designed primarily for gamma ray measurement in portable survey instruments and well logging equipment. Positioned as an intermediate-sized device, the 1B124 fits between the smaller 1B85 Thyrode and the larger 1B125 Thyrode in its physical size class.

Mechanical Construction and Physical Dimensions

The 1B124 features a robust metal envelope designed to withstand demanding field environments. The wall of the tube is constructed from brass with a density thickness of 200 mg/cm². The tube has an active length of 11 inches, which defines its sensitive detection region.

The physical dimensions of the device are as follows:

• Overall Length: 14 9/16 inches
• Main Body Diameter: 0.750 inches
• Base Diameters: 1 inch, 51/64 inch, and 15/16 inch

Base, Connections, and System Compatibility

The tube utilizes a standard RMA type A1-82 counter tube base, which is a coaxial base design. As a two-terminal device, its electrical connections are simplified into an anode and a cathode:

• Anode (A): Connected to the center pin of the coaxial base.
• Cathode (K): Connected to the outer shell/sleeve of the base.

This coaxial base configuration, combined with its nominal 900 V operating characteristics, allows the 1B124 to be interchangeable with several other counter tubes, including the 1B85 beta-gamma tube, the 1B106 mica window tube, and the 1B125 cosmic ray tube.

For physical integration into radiation detection equipment, the 1B124 is compatible with specific sockets and probes:

• Compatible Sockets: Victoreen socket types 380 and 500.
• Compatible Probes: Victoreen probe types 389 and 263-232.

Electrical Characteristics and Operating Ratings

The 1B124 operates as a high-voltage radiation detector with defined plateau and recovery characteristics. Its electrical performance parameters include:

• Operating Voltage Range: 850 V to 950 V (with a nominal center point of 900 V).
• Threshold Voltage: Maximum of 800 V.
• Plateau Length: Minimum of 200 V.
• Plateau Slope: Maximum of 3% per 100 V, measured across the voltage range of V0 = 800 V to 1000 V.
• Recovery Time: 100 microseconds.
• Background Count Rate: 200 counts per minute (c/m) when operated at V0 = 900 V.
• Service Life: Rated for 10^9 counts when tested at a rate of 6000 c/m at V0 = 900 V. The end point of its useful life is defined when the plateau slope degrades to 10% per 100 V (measured from V0 = 850 V to 950 V).

Environmental Ratings

The 1B124 is rated to operate under a wide range of environmental conditions, making it suitable for both portable outdoor survey meters and deep well logging applications:

• Ambient Temperature Range: Minimum of -10 °C to a maximum of 100 °C.
• Relative Humidity: Maximum of 100%.