Precision Radiation Instruments "Professional" Geiger Counter Model 107B "As Is"

Description

Precision Radiation Instruments "Professional" Geiger Counter Model 107B
Sold "As Is"
This is a relic of the Atomic Age, circa mid 1950s. The Precision Radiation Instruments Model 107B, known as the "Professional" was a Geiger Mueller (GM) survey instrument designed for uranium prospecting and/or civil defense.
The waterproof
CIRCUIT BOX
is constructed of a stamped steel top and bottom housing separated with a waterproof gasket and secured together with steel latches. It contains the majority of the electronic components and measures 7" x 4.75" x 4". For ease of operation the circuit box can be attached to the surveyor's belt as shown in the 2nd exhibit.
This survey meter was powered by two (2) 45 volt "B" batteries (Eveready #455 or equivalent NEDA 201), one (1) 22
1/2 volt "C" battery (Eveready #412 or equivalent NEDA 215) and two (2) 1.5 volt "D" flashlight batteries
(Eveready #D99 or equivalent)
ALL NOT INCLUDED
.
The original Eveready #455 and #412 as carbon-zinc batteries are no longer available. However, they've become available as alkaline through another brand, Exell battery. I've seen them for sale on-line (e.g. Lowe's).
The detector response is indicated by a covered standard 1/4
PHONE
jack on the top of the instrument for headphones which are included. The
COUNT RATE
could also be estimated by observing the small flashing neon light to the left of the meter dial. There are two (2) controls:
A
RANGE SWITCH
; Off, X100, X10 and X1 with four (4) scale ranges; 0.5, 0.10, 0.15, and 0.20
mR/hr. The second control is a
locked adjustment:
CALIBRATION ADJUSTMENT
on the top of the case that's covered with a cap-nut that permitted the surveyor to adjust the calibration in the field. A calibration source is provided.
It's a
1.25" in diameter
coin shape
that contains
depleted uranium
rated at 1.1 mR/hr that's stowed on a clip attached to the lower housing of the circuit box as shown in the 3rd exhibit.
The waterproof
DETECTOR PROBE
is connected to the case with a non-detachable cable. The probe has a sliding shield which may be operated by loosening a knurled head screw on the probe. When the shield is closed the instrument detects gamma rays only. With the shield open it would detect both beta and gamma rays. It housed a Victoreen Model 1B85 Thyrode thin wall aluminium Geiger Mueller (GM) tube (30 mg/cm2) which has
subsequently collapsed
as shown in the 5th exhibit.
This is mainly a "museum" or "conversation" piece.
The survey meter's interior exhibits some very minor battery corrosion in the D cell compartment as shown in the 9th exhibit which didn't effect its conductivity. This survey meter was tested with the required batteries and when powered-on the meter's needle swung all the way to the right. The neon bulb would flash intermittently and there were two (2) lamps that glowed as shown in the 10th exhibit.
Some have bypassed the search by converting these old pieces to more conventional batteries.
It would take a "Radio Shack type" to restore/upgrade this survey meter, but not entirely impossible, mainly due to its some-what simplistic design as compared to today's micro-chip technology.
This survey meter comes with headphones in the
the original carton as shown in the first exhibit. A fac
simile
of the
Operation and Maintenance Manual
that includes a schematic is included as shown in the last exhibit.
Made by Precision Radiation Instruments, Inc. Los Angeles 16, CA Serial No. 507T7522
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