Models SRJ-7 and HRJ-7 Juno Survey Meters

The reason for choosing aluminum coated with aquadag is to duplicate the
performance of a hypothetical air wall chamber as nearly as possible.
In order to give a relatively correct reading on all types of radiation
and all energies, the solid material of which a chamber is made must
nearly duplicate the ionizing properties of air and therefore have ap-
proximately the same atomic weight.
Aquadag approaches this very closely
and aluminum is the most acceptable of those metals which have satisfactory
structural properties.
B. Electrometer Tube and Grid Resistors
The electrometer tube is a specially constructed, high vacuum tri-
ode.
It requires a very low power signal on its grid to control its
plate current.
The low power input permits the use of an extremely
high grid resistor, (R-1, R-2, or R-3). Hence, a very small current
through the grid resistor will make a readily observed change in the
plate current. In turn, the plate current is conducted through a 20
microampere
meter which provides the visual indication of the level of
radiation in the chamber.
ates on 10 ma., 1.25 volts.
The CK 5886 electrometer tube filament oper-
The plate voltage is 6.5~ and the plate
current (with no radiation) is 75 micro amps.
The tube is supported on
its leads.
The base is specially treated for high insulation value in
high humidities and will probably be permanently damaged if touched
with fingers.
The three grid resistors are also specially treated.
The housing for the switch and electrometer is at bias potential so
that the ionization of air in the tube compartment will not affect the
voltage of the electrometer grid.
C. Juno Circuit
B-3 is in series with 82,000 ohms and supplies 75 micro amps to the
meter.
The electrometer tube with a plate voltage of 6.5volts, and
filasnent voltage of approximately 1.25 volts, has a plate current of
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