EXPERIMENT 12—1
_
285
tively long life. Radium D is continually producing radium F or
polonium (after an intervening substance) and this sends out the
alpha particles whose range is to be measured. The metal disc is
placed in a horizontal position and coated with a thin.layer of water
glass (sodium silicate). While this is drying, two or three pul—
verized radium D tubes are sprinkled over its surface. When dry
it is ready for use.
'
The uorescent screen G isprepared by placing the glass plate
"
in a horizontal position, covering With a thin layer of gelatin.
When thoroughly dry, soften its
with alcohol and sprinkle
with a uniform layer Of green phosphorescent zinc sulphide.
Shake off the excess powder, clear the edges and;se‘al to the end
_
of the tube with sealing wax, the luminescent material being inside.
Scintillations produced by those alpha particles which reach this
screen are observed through a small lens H.
Notes:—1. Turn the stop Cook  to admit air to the oil pump
before shutting OH its motor; otherwise oil will be sucked up into
_
the system.
‘
2. The experiment must be performed in a good dark room. It
will be necessary for the observer to ‘remainin the dark at least
ten or fteen minutes toaccustom his eyes
to the darkness and to
allow the screen to dim down before the scintillations Will be sui—
ciently bright for accurate work. A sec‘ond student should
read
the manometer and manipula‘te the stOp cocks, using a sh1elded
ruby light, or better, work
in another room, the rubber tubmg
running through the wall.
3. There are always a few scintillations occurr1ng at more or
less rare intervals on the screen. These are to be disregarded.
_
4.»Do not touch the“ surface of_the active material Wlth'thê
.
ngers.
.
.
'
_
-_
’
’
.
the barometric pressure and the tempera—
ture at the beginning and end of this experiment. Use the average
value in the calculations.
_
_
—
Set the source at _a diStance d (see gure 12—19) which is
to be
about one centimeter greater than the range
Of the particles at
'
atmospheric pressure.
Record the value of d. When the eyes have
become .accustomèd t‘othe darkness, lower the pressure slowly until
the scintillations rst appear.
this pressure…
LOW€Y the
pressure still farther, then let it increase slowly and observe the
_
285
tively long life. Radium D is continually producing radium F or
polonium (after an intervening substance) and this sends out the
alpha particles whose range is to be measured. The metal disc is
placed in a horizontal position and coated with a thin.layer of water
glass (sodium silicate). While this is drying, two or three pul—
verized radium D tubes are sprinkled over its surface. When dry
it is ready for use.
'
The uorescent screen G isprepared by placing the glass plate
"
in a horizontal position, covering With a thin layer of gelatin.
When thoroughly dry, soften its
with alcohol and sprinkle
with a uniform layer Of green phosphorescent zinc sulphide.
Shake off the excess powder, clear the edges and;se‘al to the end
_
of the tube with sealing wax, the luminescent material being inside.
Scintillations produced by those alpha particles which reach this
screen are observed through a small lens H.
Notes:—1. Turn the stop Cook  to admit air to the oil pump
before shutting OH its motor; otherwise oil will be sucked up into
_
the system.
‘
2. The experiment must be performed in a good dark room. It
will be necessary for the observer to ‘remainin the dark at least
ten or fteen minutes toaccustom his eyes
to the darkness and to
allow the screen to dim down before the scintillations Will be sui—
ciently bright for accurate work. A sec‘ond student should
read
the manometer and manipula‘te the stOp cocks, using a sh1elded
ruby light, or better, work
in another room, the rubber tubmg
running through the wall.
3. There are always a few scintillations occurr1ng at more or
less rare intervals on the screen. These are to be disregarded.
_
4.»Do not touch the“ surface of_the active material Wlth'thê
.
ngers.
.
.
'
_
-_
’
’
.
the barometric pressure and the tempera—
ture at the beginning and end of this experiment. Use the average
value in the calculations.
_
_
—
Set the source at _a diStance d (see gure 12—19) which is
to be
about one centimeter greater than the range
Of the particles at
'
atmospheric pressure.
Record the value of d. When the eyes have
become .accustomèd t‘othe darkness, lower the pressure slowly until
the scintillations rst appear.
this pressure…
LOW€Y the
pressure still farther, then let it increase slowly and observe the