EXPERIMENT 8—2
181
5. If the ionization chamber can be evacuated, reduce the
pressure to about 2 centimeters of mercury by means of an oil
pump and measure the ionization currents While increasing the
potential on the plates until ionization by collision is clearly ob—
served.
Plot this data as before.
EXPERIMENT 8—2
MEASUREMENT OF THE ABSOLUTE VALUE OF AN IONIZATION CURRENT AND THE CAPACITY OF AN ELECTROMETER
SYSTEM
1. Connect the instrument as in gure 17—13 of chapter 17 and
adjust as described in experiment 17—1. Place a small amount of
radioactive substance, whose ionization current is to be measured,
in the chamber ÂB.
2. Observe the time il for a deection of say 10 centimeters.
3. Connect a standard condenser of capacity Co in parallel With
the ionization chamber and, using the same source of ionization,
observe the number of seconds & for a deection over the same
scale divisions.
4. Measure the voltage (Av) which must be applied directly to
the quadrants to give the same deection.
5. Calculate the capacity of the quadrant system (Q’ KB) from
equations 17—2 and
Also calculate the value of the ionization current using equation 17—16.
If Co and Av are in electro—
static units and the time in seconds, the current Will likewise be in
these units.
6. If a condenser standardized for induction coefcients is avail—
able, use the method of Harms for determining the capacity of the
quadrant system.
‘
EXPERIMENT 8—3
.
A STUDY OF THE GLOW DISCHARGE
The student should read chapter 16 on Vacuum Technique
before starting this experiment.
f
The purpose of the experiment is (1) to become familiar With
the phenomena accompanying the passage of electricity through