100N — Mica End Window Radiation Counter Tube

The 100N is a low-voltage, neon-filled, halogen-quenched radiation counter tube designed primarily for the detection of beta radiation. Featuring a robust stainless steel cathode and a thin mica end window, the 100N is engineered for applications requiring high sensitivity to beta particles, long-term operational stability, and a wide operating temperature range.

Mechanical Construction and Physical Dimensions

The 100N is constructed with a cylindrical geometry featuring a thin mica window at one end to permit the entry of low-energy radiation.

Cathode and Window Specifications

• Cathode Material: Type 446 stainless steel.
• Mica Window Diameter: 1-3/32 inches (approx. 1.094 inches) effective diameter.
• Mica Window Thickness: 0.0005 inches, equivalent to an areal density of 3.5 mg/cm² or a thickness of 12.70 microns.
• Cathode Dimensions: The effective cathode length is 1.5 inches (1-1/2 inches), with an outer diameter of 1-3/16 inches (1.187 inches). The wall thickness is documented as 3/64 inches (approximately 0.047 inches) in detailed design specifications, though some general tables list a 3/32-inch wall.

Physical Dimensions and Terminals

Unlike its sister model, the 100NB, which is equipped with a 4-pin base, the standard 100N features a direct terminal connection layout:

• Overall Length: Documented as 3-3/4 inches in general reference tables, and specified as 4-3/32 ± 1/8 inches in detailed engineering drawings (which includes a 3/16-inch window guard at the front).
• Maximum Diameter: 1-1/2 inches at the widest transition section.
• Body Diameters: The window end of the tube has an outer diameter of 1.312 ± 0.005 inches, while the main body has an outer diameter of 1.187 ± 0.005 inches.
• Anode Terminal: A single pin extending from the rear of the tube, measuring 0.250 ± 0.002 inches in diameter and 1/2 inch in length.

Electrical and Performance Characteristics

The 100N operates at a lower voltage than typical argon-filled counter tubes due to its neon gas filling. Its electrical and performance parameters are optimized for stable, long-term radiation monitoring.

Operating Voltages and Plateau

• Filling Gas: Neon with a halogen quenching admixture.
• Operating Voltage: 700 V D.C.
• Starting Voltage: 625 V D.C. maximum (for 0.3-volt pulses).
• Plateau Length: In excess of 200 volts.
• Plateau Slope: Rated between 5% and 10% per 100 volts (or less than 10% per 100 volts) measured at an average counting rate of 100 counts per second.

Timing and Sensitivity

• Dead Time / Read Time: Approximately 200 microseconds.
• Maximum Counting Rate: 830 counts per second, assuming an approximate 20% dead time correction.
• Terminal Capacity: 1.0 pF.
• Radial Sensitivity: Approximately 85% to 90%.
• Background Count: 50 counts per minute maximum when shielded with 2 inches of lead (or 2 inches of lead combined with 1/8 inch of aluminum).

Environmental and Lifetime Ratings

• Operating Temperature Range: -55°C to +75°C.
• Maximum Operating Altitude: 25,000 feet.
• Life Expectancy: Unlimited by use, with a guaranteed minimum of 5 x 10^10 counts.

Related Designations and Comparisons

The 100N belongs to a broader family of mica end window counters that share physical dimensions but differ in gas filling, window thickness, or base configuration:

• 100NB: Shares identical electrical characteristics, neon filling, and performance ratings with the 100N, but is fitted with a 4-pin base. This base increases the maximum overall dimensions to 1-3/8 inches in diameter by 4-11/32 inches in length.
• 100C / 100CB: These are argon-filled counterparts designed for soft X-ray and beta detection. They operate at a significantly higher voltage of 1200 V D.C. (with a 1075 V D.C. maximum starting voltage) and feature a longer plateau in excess of 300 volts. The "CB" suffix denotes the 4-pin base version.
• 200N / 200NB: These are neon-filled alpha and beta counters. They operate at the same 700 V D.C. level as the 100N but feature a much thinner mica window (0.0002 inches, or 1.4 to 2 mg/cm² / 5.08 microns) to allow the passage of alpha particles.

Technical Summary

The 100N is a highly reliable, neon-filled, halogen-quenched mica end window counter tube designed for beta radiation detection. It operates at a nominal 700 V D.C. with a starting voltage below 625 V D.C., offering a stable plateau in excess of 200 volts with a slope of less than 10% per 100 volts. Constructed with a Type 446 stainless steel cathode and a 3.5 mg/cm² (12.70 micron) mica window, the tube provides excellent sensitivity and an unlimited operational life expectancy (guaranteed minimum of 5 x 10^10 counts). Its robust design allows it to operate reliably across a temperature range of -55°C to +75°C and at altitudes up to 25,000 feet.