Prospectors need small instruments. 
Canada's 
Department of Mines has developed 4 prototypes 
for search and assay that can be carried by hand 
or in the pocket. 
They are cheap and reliable 
FIG. 1. G-M counter has aural indication. 
First model had square case 
All-Transistor Circuits 
By G. G. EICHHOLZ, G. E. ALEXANDER and A. H. BETTENS 
Department of Mines and Technical Surveys 
Ottawa, Canada 
IN THE LAST FEW YEARS as uranium 
mining has become important among 
Canadian mining industries, a need has 
arisen for specialized radiation detec- 
tors. Asa limited demand was antici- 
pated, we undertook development of a 
number of portable detectors. 
The characteristics of five of them 
are tabulated on p. 92. They have 
completely transistorized circuits for 
light weight and compactness. Cir- 
cuits are kept as simple as possible, and 
circuit ‘‘building blocks” are stand- 
ardized as much as possible. The 
units are intended as prototypes to 
stimulate commercial production. 
High-voltage supplies. High-volt- 
age circuits were largely based on a 
simple oscillator power supply (1, 2) 
modified to suit the particular require- 
FIG. 4. Directional counter has either 
speaker or meter indication 
50 
ments. Earlier designs with vibrator 
power supplies (3) have proved un- 
satisfactory because of limited life, 
large bulk, and high battery drain. 
Portable G-M Counter 
To avoid the bulkiness of most 
portable G-M counters we chose a 
G-M tube first and designed around it. 
The tube has to be large, halogen- 
quenched for long life, and preferably 
low-voltage. 
For a rugged, lightweight, general- 
purpose survey instrument it was 
decided to use aural indication only. 
Brush BB-134 hearing-aid* and Argo- 
nne microphones were found to be 
small enough yet loud enough. 
Co., Cleveland 
* Brush Electronics 
Ohio. 
Two mechanical designs were made. 
The first was in a square box (Fig. 1), 
but the later model in a case of ellip- 
tical cross section fits the hand much 
better (Fig. 2). Both are powered by 
three penlight batteries, Eveready 
No. 912 or equivalent. The circuit 
consists of only an oscillator power 
supply with voltage tripler and direct 
aural indication (Fig. 3). 
Tests show that it is advisable to 
coat the G-M tube with black paint 
or to wrap it with friction tape to re- 
duce its photosensitivity. 
Directional G-M Counters 
Another problem was to make a 
directional counter for underground 
use in uranium mines Preliminary 
| Meg 
|Meg 
T1-Ferroxcube, Primary: 45 turns tapped at 20, Secondary: 2,000 turns. 
T2-Hammond |42J 
FIG. 5. Speaker model of directional counter has this oscillator-doubler circuit. 
Life is, 
limited by relatively large battery drain of 8 ma 
