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EXPERIMENT 8—1
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179
mounted along the axis of the cathode and thegrid is located
between these electrode$.
The rectifying action of a glow dis—
charge With large cathode and small anode has been discussed previously. In the hot—cathode tubes, high efciency dull emitter
cathodes are used.
If the positive ions which bombard' the la—
ment possess too great an energy, above the disim‘egmz‘ion voltage
(about 30 volts), the emitting surface Will be destroved. If, therefore, the plate voltage is applied before the lament has reached
—
the normal operating temperature, the high voltage aCross the tube
Will give the positive ions a destructively high velocity and the
lament Will be ruined or its life shortehed.
The lamentmust be
hot before the plate voltage is applied. However, after the la—
ment is heated, and a discharge started, the voltage across the
tube falls to a comparatively xed value (of 10—20 volts) charac—
.
teristic of the pressure in the tube, as discussed before.
It is for-,
tunate that there is a small range of voltage between the disinte—
.
-
gration voltage and'the ionizing potential needed to create ions in
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the gas.
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EXPERIMENT 8—1
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IONIZATION CURRENT MEASUREMENT WITH A
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QUADRANT ,E‘LECTROMETER° _‘
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The purpose ofthis experimetisü observe
the current— through
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a
at atmospheric pressure
acceleratingpotentials.
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