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.