120N — Radiation Counter Tube
A permanent sensitivity, stainless steel radiation counter tube designed for beta radiation detection applications.
Overview
The 120N is a specialized radiation counter tube designed primarily for the detection of beta radiation. It features a robust physical construction characterized by a stainless steel cathode and a thin mica window. The tube utilizes a neon gas filling with a quenching admixture to achieve stable electrical characteristics and a long operating life.
Engineered for reliability under diverse environmental conditions, the 120N operates over a wide temperature range and offers a life expectancy that is unlimited by use. Its electrical design is optimized for a nominal 700 V D.C. operating voltage, providing a wide plateau and controlled background noise characteristics.
Physical Construction and Dimensions
The mechanical design of the 120N is tailored to facilitate the entry and detection of beta particles while maintaining structural integrity. The tube is built with a stainless steel cathode, ensuring resistance to degradation and consistent performance over time.
The physical dimensions and structural specifications of the tube include:
- Cathode Dimensions: The effective cathode measures 2-11/16 inches in length, with an outer diameter (O.D.) of 2 inches and a wall thickness of 5/64 inches.
- Mica Window: To permit the penetration of beta radiation into the active volume, the tube features a thin mica window with an effective diameter of 1-29/32 inches. The window has an average thickness of 0.0008 inches, which corresponds to an areal density of 5.6 mg/cm² or a physical thickness of 20.32 microns.
- Overall Tube Dimensions: The maximum overall dimensions of the tube housing are 2-3/8 inches in diameter by 5-1/8 inches in length.
- Operating Temperature Range: The tube is rated to operate reliably at temperatures ranging from -55°C to +75°C.
Electrical and Detection Characteristics
The 120N relies on a neon gas filling combined with a quenching admixture to facilitate the ionization and quenching cycles necessary for radiation counting. Its primary electrical and operating parameters are:
- Operating Voltage: 700 V D.C.
- Plateau Length: The operating plateau extends in excess of 200 volts, providing a broad voltage range where the count rate remains relatively stable.
- Plateau Slope: The slope of the plateau is rated between 5% and 10% per 100 volts.
- Dead Time: The approximate dead time of the tube is 300 microseconds, which defines the minimum interval required between successive ionizing events for individual detection.
- Background Count: When placed within a shielded enclosure featuring a 2-inch lead shield, the background count of the tube is limited to a maximum of 100 counts per minute.
Related Variants and Comparisons
The 120N is part of a broader family of radiation counter tubes that share similar physical dimensions or operating principles but differ in their specific configurations:
- 120NB: This variant shares identical electrical characteristics with the 120N, including a 700 V D.C. operating voltage, a plateau in excess of 200 volts, a 300-microsecond dead time, and a maximum background count of 100 counts per minute. It also utilizes the same cathode and mica window dimensions. However, the 120NB is equipped with a 4-pin base and has slightly different maximum overall dimensions of 2-5/16 inches by 5-3/4 inches.
- 120C: While sharing the same physical cathode dimensions, mica window diameter, and window thickness as the 120N, the 120C utilizes an argon and quenching admixture filling instead of neon. This gas composition shifts its nominal operating voltage to 1200 V D.C., extends its plateau to in excess of 300 volts, and expands its application scope to include both Beta and X-Ray detection.
Technical Summary
The 120N is a neon-filled, self-quenched radiation counter tube designed for beta detection. It features a stainless steel cathode measuring 2-11/16 inches by 2 inches O.D., a 1-29/32 inch effective diameter mica window, and a maximum overall size of 2-3/8 inches by 5-1/8 inches. Operating at 700 V D.C. with a plateau exceeding 200 volts, the tube exhibits a plateau slope of 5% to 10% per 100 volts, an approximate dead time of 300 microseconds, and a maximum shielded background of 100 counts per minute. Its construction ensures an unlimited life expectancy across an operating temperature range of -55°C to +75°C.
