sented in Fig. 12. The power-supply 
circuit is contained in a shielded sec- 
tion of the detector unit. A 6-pin 
Jones plug completes the supply cir- 
cuits when the portable unit is detached 
from its cradle. The meter is a 134-in. 
Simpson Model 182, 100 wa full scale. 
The alarm system consists essentially 
of a Type 705 Weston Sensitrol meter 
relay in series with the detector meter. 
When the relay is tripped, it closes the 
buzzer circuit, which derives its power 
from the car battery. The relay is 
reset manually, and its sensitivity is 
controlled by the detector-range switch. 
Figure 13 shows the instrument. 
The choice of battery posed a definite 
problem. Easiest solution for a car- 
borne unit is to operate the whole 
system from the car battery. How- 
ever, in the present case it was felt to 
be preferable to keep the scintillation 
detector self-contained for independent 
use. Rechargeable batteries permit 
long uninterrupted service. Thechoice 
of suitable lightweight batteries proved 
rather limited, and the type selected 
in the end is the Yardney Silvercel type 
LR-05.* These are lightweight zinc- 
silver cells with an alkaline filling. 
Unfortunately they are very sensitive 
to overcharging, and to protect them 
it is necessary to charge them from the 
car battery while the car engine is not 
running. The circuit shown is in- 
tended for operation of the detector 
system insulated from the car body. 
This makes it independent of the 
grounding of the car battery, but the 
connection to plug Pl must be made 
as shown. 
* Yardney Electric Corp., 105 Chambers 
8t., N. Y., N. Y. 
Weston Sensitrol relay 
Gime D 
7 ap 
i 
6 Pin Jones Plug 
FIG. 12. Circuit for carborne unit 
includes buzzer operated from car 
battery to indicate high counting 
rate and rechargeable batteries in 
portable section 
FIG. 13. Top section of carborne 
detector is hand-portable Be 
In this development mechanical de- 
sign has been varied as much as possi- 
ble to investigate different approaches, 
and further changes will probably be 
required for commercial production. 
The work has demonstrated that con- 
siderable economies are possible in size, 
weight, and component requirements. 
There is also indication that diver- 
gence in design is to be expected as use 
of radioactivity spreads and higher 
specialization is required. Instrument 
cost and complexity grow steadily, but 
at the same time we should realize the 
savings that are possible by develop- 
ments in simpler instrumentation. 
T1-Primary: 40 turns No.27 enameled wire tapped at " turns, 
Secondary: 2,500 turns No.36 enameled wire 
FIG. 11. 
Circuit for portable scintillation detector of Fig. 10 
Plug to car battery” ¢ 
eee tin oF 
prey : 
3-pole, 3- position switch 
Ti- Primary: 40 turns No.27 enameled wire tapped at 
\l turns, Secondary: [500 turns No.36 enameled wire 
* * * 
The work described here has benefited from 
the cooperation of many of our colleagues at 
the Mines Branch. Thanks are due par- 
ticularly to L. S. Collett and R. B. Rowe of 
the Geological Survey of Canada for initial 
discussion of requirements and for assistance 
with field tests, to G. Meilleur for his skillful 
workmanship and many suggestions concern- 
ing the mechanical design of the units, to 
E. Hausmann of Canadian Benaudi Ltd. for 
the gift of a miniature speaker unit and to 
J.V. Krzyzewski and C. A. Josling for their 
assistance in the construction of the units and 
the drafting of circuits. 
This article is based on Mines Branch 
Topical Report TR-136/56 and published by 
permission of the Director, Mines Branch, 
Ottawa. 
BIBLIOGRAPHY 
1. G. E. Alexander. A transistor high voltage 
power supply for portable Geiger counters, 
Mines Branch Report TR-125/54 (November 
1954) 
2. A. H. Bettens, G. G. Eichholz. Transistorized 
high voltage power supplies (in preparation) 
8. A. H. Bettens, C. Lapointe, G. G. Eichholz. 
Portable directional Geiger counters, Mines 
Branch Report TR-122/54 (August 1954) 
4. C. M. Lapointe, A. H. Bettens. U.S., Patent 
application Serial No. 508,724 (May 16 1955) 
6. G. G. Eichholz, A. O. Smith, A. Bauer. Trans 
Can. Inst. Mining Met. 60, 59 (1957) 
6. H. H. Schwartz. Portable scintillation coun- 
ters, Mines Branch Internal Report IR-183/55. 
(November 1955) 
53 
