RCL Gas Flow Counter (ca. 1953-1960)

RCL Gas Flow Counter

This is a windowless gas flow counter designed to operate in either the proportional or Geiger mode. Although it carries no model number or other type of identification, it is clear that it was manufactured by Radiation Counter Laboratories, Inc, of Skokie, Illinois. Prior to 1955 or so, it was known as the Mark 12 Model 2. Later, it became known as the Model 10200.

The upper part of the unit contains a cylindrical counting chamber. The lower rotating section contains three sample wells. One well, containing the sample being counted, is positioned under the chamber. While the counting is in progress, the second well, also containing a sample, is being purged (pre-flushed)—this takes 1-2 minutes. The third well is positioned at the front to accept the next sample. The glass chamber on the side of the counter (upper right in photo) is used to monitor the gas flow. This is done by observing the rate at which the gas bubbles through the oil in the glass chamber. Typical flow rates are on the order of 1-3 bubbles per second.

Counting gas:

  • GM: Helium, isobutene (quench mix flow gas)
  • Proportional: Pure methane

Operating voltage:

  • GM: 1300 volts
  • Proportional:
    • Alpha 2700 volts
    • Beta 3900 volts

Sample well diameter: 1 1/32”

Size: 4.5” in diameter x 2.5” high

Weight: 6.5 pounds

Material: Chrome-plated brass

Donated by Ron Kathren.


  • RCL Radiation Detectors Catalog, no date.
  • Atomic Energy Commission Radiation Measuring Instruments RIB (Part 2) Supplement, page BG-5Q, July 1, 1954.