'
8—3“.
IONIZATlON
'
159 '
sent the total number of ions produced by the source, and the
recombination rates may be diHerent in different cases.
The potential which must be applied acroSs the plates of the
ionizatioh chamber in order to
a degree of
suP—
ciently complete for practical purposes is dierent in different
experiments but may be roughly stated as between 50 and 200
volts per centimeter for ions produced bythe beta and gamma
rays of radioactive substances.
In these cases, the ions are produced uniformly in the gas in the ionization chamber, but with
alpha particles the ions are produced in high concentration along
.
_
a narrow beam.
Rapid recombination results, requiring the use of '
several thousand volts per centimeter to.give saturation. Further,
—
the potential necessary
to produce saturation depends on the
'
density and kind of gas being ionized, the distance between the
'
‘
plates and the presence
dust or moisture; »However, if the sat_
uration current is given in amperes per
volt per cubic centimeœr
of air at standard pressure and temperature, it is an accurate speci—
‘
'
cation of the intensity of the source of ionization. For uniformly
ionized gaseS the value of the saturation current increases as the‘
total mass of gas betWeen the plates is
If, ”now, the potential “is still further increased the particles
travel with greater and greattefvelocities (particularly the nega—
.
tive charges) until
energy to break up
_
_
neutra—l atoms at
new positive
;
charges are
under]
eld'ahd' _‘
f
_‘ inerease
of B in gure
Thisra1d1ncreaseœntmuesuntWith rising—
‘
observe wmwwnôywlàsatatmosphempæssure1t
_
‘
topartlallyevacuatetheregwnbetweentheplates
-
‘
‘
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uœd
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