Predecessor to the Reuter-Stokes RS 111 Pressurized Ion Chamber (early 1960s)

Predecessor to the Reuter-Stokes RS 111 Pressurized Ion Chamber

The instrument pictured here was the predecessor of the famed Reuter-Stokes RS-111 pressurized ion chamber. The latter became known as the "gold standard" for real-time gamma measurements in the environment.  For obvious reasons, this early design was referred to as the "fire extinguisher."

Although pressurized ion chambers (PICs) had been used for many years in the study of cosmic rays, the idea to use them to measure environmental exposure rates originated at the Health and Safety Laboratory (better known as HASL) in New York City. The impetus was the desire to assess the fallout generated by above ground nuclear tests.

For the most part, Harold Beck and Bill Condon at HASL designed the electronics for the "fire extinguisher" while the design of the ion chamber was handled by Art Stokes of Reuter-Stokes. The heart of the electronics package was a Victoreen vibrating reed electrometer - something HASL had on hand at the time.

Only a couple of the original of the fire extinguisher units were constructed (in the early 1960s) and these were exclusively used at HASL. The one in the ORAU collection pictured here is HASL PIC #1! 

Sometime around 1970, HASL switched to a unit that employed a spherical ion chamber. The latter was coupled to electronics using a MOSFET electrometer designed at HASL. This formed the basis of the design Reuter-Stokes produced commercially as the RS-111.

The extreme sensitivity of the unit derived from the large volume of the ion chamber and the high pressure of the gas.

Readout: The readout simply indicated the voltage drop across the unit's high meg resister. There were five range switch settings: 3, 10, 30, 100 and 300

Sensitivity: Approximately a few uR/hr up to 100-200 uR/hr

Size: ca. 33" high (the cylindrical aluminum electrometer housing is 9" in diameter) 

Fill gas: Argon at approximately 40 atmospheres

Donated by Reuter-Stokes courtesy of Dan McCormick.

Predecessor to the Reuter-Stokes RS 111 Pressurized Ion Chamber
Predecessor to the Reuter-Stokes RS 111 Pressurized Ion Chamber

The above photo taken in the early 1960s shows the "fire extinguisher" at work. The detector to the right is a NaI gamma scintillator connected to a 256-channel analyzer in the van (Miller and Larsen 2002)


  • Harold Beck. Personal communication.
  • Miller and Larsen. "Field-based measurement methods for radioactive fallout assessment." Health Physics. Vol. 82 (5). May 2002.
  • The reference to get, and one I haven't found yet, is DeCampo, Beck and Raft's. "High-pressure argon ionization chamber systems for the measurement of environmental radiation exposure rates." HASL-260: 1-69. 1972.