Model 109 "Professional" (1952)

Model 109 "Professional" (1952)

The Precision Radiation Instruments Model 109, just like the Model 107, was also known as the “Professional.” The major difference between the two was that the Model 109 employed an end window Geiger Mueller detector and was intended for either laboratory work or civil defense measurements (e.g., of food and water). There was no speaker to provide an audible signal but there was a covered jack on the top of the instrument for headphones. The count rate could also be estimated by observing the small flashing neon light to the left of the meter face. A locked adjustment on the top of the unit permitted the surveyor to adjust the calibration. The assigned date of 1952 is based on a July 1952 date on the instrument calibration curve (attached to the instrument case).

Detector: end window GM tube (1.4 mg/cm2), connected to the meter with a non-detachable cable

Range: 0-0.2, 0-2 and 0-20 mR/h

Batteries: Two 1.5 volt, two 45 volt and one 22.5 volt

Dimensions: 3.5” x 4.5” x 6.5”

Weight: 7 pounds

Price: $199.50 in 1954

For some reason, maybe it was just a part of being in LA, Precision Radiation Instruments was also in the music business. While none of the PRI-owned labels (Craftsman, Tops, etc) were household names, they did produce records for some reasonably well known entertainers such as Mel Torme and Lena Horne. One PRI 33 1/3 record worth mentioning: "If the Bomb Falls," a primer on surviving a nuclear attack.


  • Atomic Energy Commission Radiation Measuring Instruments RIB (Part 2) Supplement, page SGM-58A, July 1, 1954.
  • Precision Instruments catalog, form 1001B, 1954 copyright.