Models SRJ-7 and HRJ-7 Juno Survey Meters

OPERATING TEMPERATURE
RANGE :
35OF. TO 135OF.
SRJ -7
HRJ -7
CASE :
HANDLE :
WE I GHT :
HARD-CHROME PLATED ALUMINUM WITH ENGRAVED MARKINGS
ON TOP OF CASE; GASKETED, DUST AND MOISTURE RESIST-
ANT. DIMENSIONS: 11 1/2" L. x 5 3/4" W. x 6 1/2"
H. e
ALUMINUM ESPECIALLY CAST LOW-POROSITY, SMOOTHLY
POL I SHED.
6 LBS. 11 oz. NET.
I l l . THEORY OF OPERATION
A. IONIZATION CHAMBER.
THE IONIZATION CHAMBER IS A RECTANGULAR ALUMINUM CASE, (THE INSIDE
OF WHICH is COATED WITH AQUADAG) LOCATED IN THE FORWARD END, BOTTOM OF
THE JUNO CASE. AIR AT ATMOSPHERIC PRESSURE IS THE IONlZATtON MEDIUM.
THE COLLECTOR, AN ALUMINUM ROD COATED WITH AQUADAG, IS EXTREMELY WELL
INSULATED BY MEANS OF A
TEFLON SUPPORT BUSHING.
ALPHA,
BETA AND/OR
GAMMA RADIATION, WHEN PASSING THROUGH THE CHAMBER, COLLIDES WITH INDIVID-
UAL MOLECULES OF AIR. A COLLISION CAUSES AN ELECTRON TO BE DISPLACED
FROM ITS NORMAL ENERGY LEVEL. ONCE REMOVED SUFFICIENTLY FAR FROM ITS
NORMAL ENERGY LEVEL IT IS SUBJECTED TO STATIC ELECTRIC FORCE. THIS
FORCE PULLS THE FREE ELECTRON TO THE COLLECTOR WHICH IS 90 VOLTS POSI-
TIVE WITH RESPECT TO THE CHAMBER WALLS. THE MOLECULE, OR ATOM, AFTER
LOSING AN ELECTRON ASSUMES A POSITIVE POTENTIAL (SUCH A CHARGED ATOM IS
CALLED AN ION) AND IS ATTRACTED BY THE NEGATIVELY CHARGED WALLS. SINCE
THE COLLECTOR IS WELL INSULATED THE ELECTRONS WHICH LAND ON ITS SURFACE
BUILD UP A CHARGE, RESULTING IN A MORE NEGATIVE POTENTIAL. THIS NEGA-
TIVE SHIFT IN THE COLLECTOR IS WHAT IS DETECTED BY THE ELECTROMETER CIR-
CUIT. THE REASON FOR CHOOSING ALUMINUM COATED WITH AQUADAG IS TO DUPLI-
CATE THE PERFORMANCE OF A
HYFOTHETICAL A I R WALL CHAMBER AS NEARLY AS POS-
SIBLE. 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 APPROXIMATELY THE SAME ATOMIC WEIGHT. AQUA~AG APPROACHES THIS
CLOSELY AND ALUMINUM IS THE MOST ACCEPTABLE OF THOSE METALS WHICH HAVE
SATISFACTORY STRUCTURAL PROPERTIES.
B. ELECTROMETER TUBE AND GRID RESISTORS.
VERY
THE ELECTROMETER TUBE IS A SPECIALLY CONSTRUCTED, HIGH VACUUM PENTODE
WHICH IS OPERATED AS A TRIODE. 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-I, 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.
THE CK 5886 ELECTROMETER TUBE
FILAMENT OPERATES ON 10 MA., 1.25 VOLTS. THE PLATE VOLTAGE IS 6.5' AND
THE PLATE CURRENT (WITH NO RADIATION) IS 80 MICROAMPS. THE TUBE IS
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