238
10.
POSITIVE RAYS AND lSOTOPES
The scintillation screen (S) can be obtained from a burned out
_
-
cathode’ray oscillograph tube or prepared by coating a glass plate
With a thin layer of phosphorescent zinc sulphide or with willemite. .
A trace of saliva or gelatin is used as a binder. The tube (E) may
be of glass or metal.
Procedure—The apparatus is evacuated to as low a pressure as
possible through the large tube (T), which should be at least 2.5
centimeters in diameter.
It should be impossible to pass a discharge
'
through the tube when 40 to 60 kilovolts are applied between Â
and C.
The high voltage may be obtained by the use of a trans—
former and rectier tube as in experiment 3—1. A static machine
may be used but does not give good intensity. A Bunsen burner
-
With a small blue ame is now used to warm the palladium thimble
(P).
hydrogen ows through P into the discharge tube.
Adjust the heating until, with the vacuum pumps in operation, a
faint blue discharge is just visible in the tube. A spot of light
should be seen at the center of the screen (S). Apply both the
.
magnetic and electric deecting elds and observe the positive ray _
parabola with varying eld strengths.
If conditions are suf-*
ciently steady, measurements can be made and E/M and 0 of the
positive ions calculated; or the parabola may be photographed.
Preeauliom.—l. Ground the cathode.
Keep away from the
emode.
2. Be sure the cathode is water cooled before starting the
discharge. 3. Do not heat the palladium tube beyond a very dull
_
red.
_
If there is breakdown of the glass near the cathode, slip a snugly
tting iron tube over its end. Let the iron tube extend beyond C, -
toward Â, about 5 centimeters.
’
_
REFERENCES
_
_
:
:
_
1. A. ]. Dempster, Phys. Rev., 15, 138 (1920).
'
’
'
’
»
2. ]. ]. Thomson, Phil. Mag., 13, 561 (1907).
,
__
"
"
?>. See Harnwell and Livingoo‘d, Experimental Atomic Physics, McGraw—
Hill Book Co. (1933), page 136.
.
…
,
.
_
4. General Reference A, page 73. ‘ "
:_
_
’
-
.
—
‘
_
5. General Reference A, pages 82 and 86.
_6. General Reference A, Chapter IV.
_
.
.
-
7.' A.
Phys. Rev., 11, 316 (1918); 20, 631
,
8. K. T. Bainbridge, _Îr. Frank. Inst., 215,509 (1933).
-
'
'
-
'
10.
POSITIVE RAYS AND lSOTOPES
The scintillation screen (S) can be obtained from a burned out
_
-
cathode’ray oscillograph tube or prepared by coating a glass plate
With a thin layer of phosphorescent zinc sulphide or with willemite. .
A trace of saliva or gelatin is used as a binder. The tube (E) may
be of glass or metal.
Procedure—The apparatus is evacuated to as low a pressure as
possible through the large tube (T), which should be at least 2.5
centimeters in diameter.
It should be impossible to pass a discharge
'
through the tube when 40 to 60 kilovolts are applied between Â
and C.
The high voltage may be obtained by the use of a trans—
former and rectier tube as in experiment 3—1. A static machine
may be used but does not give good intensity. A Bunsen burner
-
With a small blue ame is now used to warm the palladium thimble
(P).
hydrogen ows through P into the discharge tube.
Adjust the heating until, with the vacuum pumps in operation, a
faint blue discharge is just visible in the tube. A spot of light
should be seen at the center of the screen (S). Apply both the
.
magnetic and electric deecting elds and observe the positive ray _
parabola with varying eld strengths.
If conditions are suf-*
ciently steady, measurements can be made and E/M and 0 of the
positive ions calculated; or the parabola may be photographed.
Preeauliom.—l. Ground the cathode.
Keep away from the
emode.
2. Be sure the cathode is water cooled before starting the
discharge. 3. Do not heat the palladium tube beyond a very dull
_
red.
_
If there is breakdown of the glass near the cathode, slip a snugly
tting iron tube over its end. Let the iron tube extend beyond C, -
toward Â, about 5 centimeters.
’
_
REFERENCES
_
_
:
:
_
1. A. ]. Dempster, Phys. Rev., 15, 138 (1920).
'
’
'
’
»
2. ]. ]. Thomson, Phil. Mag., 13, 561 (1907).
,
__
"
"
?>. See Harnwell and Livingoo‘d, Experimental Atomic Physics, McGraw—
Hill Book Co. (1933), page 136.
.
…
,
.
_
4. General Reference A, page 73. ‘ "
:_
_
’
-
.
—
‘
_
5. General Reference A, pages 82 and 86.
_6. General Reference A, Chapter IV.
_
.
.
-
7.' A.
Phys. Rev., 11, 316 (1918); 20, 631
,
8. K. T. Bainbridge, _Îr. Frank. Inst., 215,509 (1933).
-
'
'
-
'