152
7. "THE OUTER PARTS OF THE ATOM
‘
7—9.
may now say
that the atom contains
a massive, positively charged nucleus around which negative electrons are Conned in known energy levels.
EXPERIMENT 7—1
,
MINIMUM IONIZING POTENTIALS
The purpose of this experiment is to measure the minimum
ionizing potentials of various gases such as nitrogen, hydrogen,
helium and argon using three—electrode vacuum tubes.
Preparation of the tube may be made by the instructor or by
'
the advanced student in the following manner.
Secure a radio
tube such as the 01A and make a small hole in its top either
with a ame or by cutting of the tip. Seal on a piece of soft
glass tubing which contains a constriction a short distance from its
_
end.
Then seal this to a good vacuum system, blowing through a
drying tube, and evacuate until an electrical discharge can no '
longer be made to pass through the system.
(Note: If the la—
ment is left exposed to the air for more than a few hours, water
vapor Will ruin it.)
If possible, it is advisable to outgas the grid
and plate. (See the chapter on Vacuum Technique.) Now
admit a little of the gas to be tested and re—evacuate as thoroughly
as possible. Let in a little of the gas again and start the evacu— '_
ation but close of? the system from the pumps
when the pressure
'
is around one-half mm. Anywhere from 1.0 mm. to 0.005 mm.
'
will serve.
The lower pressures are better although the amount
'
of the positive ion currents measured will be small. The degree
—
of
be crudely estimated by the distance
between
:.
the striations.
This
to about 1 mm. for a pressure
_-of 1 mm. and 1 or 2 cm. for a pressure around 0.05 mm. The
.
constricti0n is now closed,‘ using as small a ame as possible,
and
,
the tube removed from the system.
It is now ready-for use. Of
—
course the experiment may be carried out without remoVing it
from thefevacuation system.
,
-
‘
,
-
as
in gure 7—7. The grid-voltage potentiometer
should, permit Variations of 0.1 to 0.5 volts. A 3000 ohm poten—
7. "THE OUTER PARTS OF THE ATOM
‘
7—9.
may now say
that the atom contains
a massive, positively charged nucleus around which negative electrons are Conned in known energy levels.
EXPERIMENT 7—1
,
MINIMUM IONIZING POTENTIALS
The purpose of this experiment is to measure the minimum
ionizing potentials of various gases such as nitrogen, hydrogen,
helium and argon using three—electrode vacuum tubes.
Preparation of the tube may be made by the instructor or by
'
the advanced student in the following manner.
Secure a radio
tube such as the 01A and make a small hole in its top either
with a ame or by cutting of the tip. Seal on a piece of soft
glass tubing which contains a constriction a short distance from its
_
end.
Then seal this to a good vacuum system, blowing through a
drying tube, and evacuate until an electrical discharge can no '
longer be made to pass through the system.
(Note: If the la—
ment is left exposed to the air for more than a few hours, water
vapor Will ruin it.)
If possible, it is advisable to outgas the grid
and plate. (See the chapter on Vacuum Technique.) Now
admit a little of the gas to be tested and re—evacuate as thoroughly
as possible. Let in a little of the gas again and start the evacu— '_
ation but close of? the system from the pumps
when the pressure
'
is around one-half mm. Anywhere from 1.0 mm. to 0.005 mm.
'
will serve.
The lower pressures are better although the amount
'
of the positive ion currents measured will be small. The degree
—
of
be crudely estimated by the distance
between
:.
the striations.
This
to about 1 mm. for a pressure
_-of 1 mm. and 1 or 2 cm. for a pressure around 0.05 mm. The
.
constricti0n is now closed,‘ using as small a ame as possible,
and
,
the tube removed from the system.
It is now ready-for use. Of
—
course the experiment may be carried out without remoVing it
from thefevacuation system.
,
-
‘
,
-
as
in gure 7—7. The grid-voltage potentiometer
should, permit Variations of 0.1 to 0.5 volts. A 3000 ohm poten—