Precision Radiation Instruments "Drill Hole" Geiger Counter Model 120 "As Is"

Description

Precision Radiation Instruments "Drill Hole" Geiger Counter Model 120
Sold "As Is"
In 1955 Precision Instruments introduces the model 120 Geiger Counter known as the "Drill Hole" for uranium prospecting of drill holes as deep as 1000 feet. It was essentially the model 107B with the option of attaching a long cable and drill hole probe. It had an extra drill hole probe and 50" of cable. The drill hole probe was 7/8 " in diameter. It originally came with the standard model 107B probe as well as the longer drill hole probe. The drill hole probe and long cable are
NOT INCLUDED
in this listing and
neither are they available separately
.
The waterproof survey meter is constructed of a two-piece case made of stamped steel separated with a waterproof gasket. The waterproof Detector Probe is connected to the case with a 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 will detect both Beta and Gamma rays. It houses a thin wall aluminium Geiger Mueller (GM) tube (30 mg/cm2) as shown. Also INCLUDED is an adjustable canvas shoulder strap with hook clips at opposite ends as shown in the first exhibit.
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 three (3) scale ranges; 0.2, 2, and 20
mR/hr. The second is a
locked adjustment:
CALIBRATION ADJUSTMENT
on the top of the case that permitted the surveyor to adjust the calibration-a source was provided
(usually a source of depleted uranium) so
that the calibration could be performed in the field. This black coin shaped source was attached to the case (lower right) as shown in the 8th exhibit and is
NOT INCLUDED
.
It 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" type flashlight cell batteries
(Eveready #D99 or equivalent)
NOT INCLUDED
.
This is mainly a "museum" or "conversation" piece.
The meter as a whole appears to exhibit very little cosmetic wear and tear and the interior is remarkably preserved with no signs of battery corrosion which is common with this vintage units. This survey meter was not tested recently due to the unavailability of the necessary batteries.
The original Eveready #455 and #412 as carbon zinc batteries are no longer available. However, they have now become available as alkaline through another brand, Exell battery which can be purchased on-line.
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.
A
facsimile
of the
Operation and Maintenance Manual
for a similar model 107B is included which shows a schematic as shown in the exhibits.
Made by Precision Radiation Instruments, Inc. Los Angeles 16, CA Serial No. 20T2587
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