352
15.
COSMIC RAYS
with their great energies, billions of volts, may be used in nuclear
disintegrations.
EXPERIMENT 15—1
.
THE ABSORPTÏON OF COSMIC RAYS
The circuit of gure 15—4 may be used.
The chamber (Â)
may
be co‘nstructed of seamless steel tubing % inch thick, 2 to
3 inches in diameter and 12 inches long inside. The chamber is
to be lled with a gas
at high pressure
and must, therefore, have
carefully constructed ends. The gas pressure should be 30 to 50
_
atmospheres in order that sufcient ion pairs be produced to give
an
ionization current appreciably greater than the natural leak
of the equipment. Air may be used. Oxygen is comparable to
air, carbon dioxide or nitrogen somewhat better and argon very
much better.
If the gas is not free from radioactive contaminations, the natural leak will be found to be large. All parts of the '
equipment must be dry. The insulating plug is made of amber
and so designed as to withstand the pressure
in the chamber.
The collecting rod (B) is a
steel rod passing through the
plug and running axially along the center of the cylindrical cham'
her to approximately one inch of the opposite end. Non-radio—
active metals, tested with an electroscope, are placed around and
under the chamber.
Three to four inches of lead or of iron Slabs
should be used.
As is usual with electrometer technique, and
especially true here, the lead wires to the insulated quadrants of
the electrometer as well as the switch (K) must be carefully
shielded in grounded metal tubes
cases.
The voltage (17)'
is to be of the order of 100 to 200 volts.
The experiment should
only be attempted with a sensitive electrometer, as the currents
are of the order of
amperes and less.
It should be carried
.
'
out in a room which is free from radioactive contaminations.
;
'
Slabs of iron, free from contamination, of % to 1—inch thickness, Which cover the chamber are to be placed over it. The rate of '
,
deection of the electrometer
as increasing layers of
;
iron are added, up
to about one foot total.
These rates are pro_portional to the. cosmic ray intensity and are to be plotted against
‘
!
the total thicknesses of iron to obtain a curve of the absorption
of
the softer cosmic rays which reach the earth’s surface.
.
15.
COSMIC RAYS
with their great energies, billions of volts, may be used in nuclear
disintegrations.
EXPERIMENT 15—1
.
THE ABSORPTÏON OF COSMIC RAYS
The circuit of gure 15—4 may be used.
The chamber (Â)
may
be co‘nstructed of seamless steel tubing % inch thick, 2 to
3 inches in diameter and 12 inches long inside. The chamber is
to be lled with a gas
at high pressure
and must, therefore, have
carefully constructed ends. The gas pressure should be 30 to 50
_
atmospheres in order that sufcient ion pairs be produced to give
an
ionization current appreciably greater than the natural leak
of the equipment. Air may be used. Oxygen is comparable to
air, carbon dioxide or nitrogen somewhat better and argon very
much better.
If the gas is not free from radioactive contaminations, the natural leak will be found to be large. All parts of the '
equipment must be dry. The insulating plug is made of amber
and so designed as to withstand the pressure
in the chamber.
The collecting rod (B) is a
steel rod passing through the
plug and running axially along the center of the cylindrical cham'
her to approximately one inch of the opposite end. Non-radio—
active metals, tested with an electroscope, are placed around and
under the chamber.
Three to four inches of lead or of iron Slabs
should be used.
As is usual with electrometer technique, and
especially true here, the lead wires to the insulated quadrants of
the electrometer as well as the switch (K) must be carefully
shielded in grounded metal tubes
cases.
The voltage (17)'
is to be of the order of 100 to 200 volts.
The experiment should
only be attempted with a sensitive electrometer, as the currents
are of the order of
amperes and less.
It should be carried
.
'
out in a room which is free from radioactive contaminations.
;
'
Slabs of iron, free from contamination, of % to 1—inch thickness, Which cover the chamber are to be placed over it. The rate of '
,
deection of the electrometer
as increasing layers of
;
iron are added, up
to about one foot total.
These rates are pro_portional to the. cosmic ray intensity and are to be plotted against
‘
!
the total thicknesses of iron to obtain a curve of the absorption
of
the softer cosmic rays which reach the earth’s surface.
.