,
'
,
9—4.
INTENSITY MEASUREMENTS
197
pfoduces the same blackening-‘as the former. The beams are
then of equal intensity. This prOcedure is used in experiment 9—1.
When x-rays pass through a gas, photo-electrons are ejected
from the molecules in the same manner as photo—electrons are
ejected from a gas by ultra—violet light. The total number of
ions which the photo-electrons in turn produce in the gas is far
greater than their own number.
Thus, the ionization of a gas by
_x-rays is, to a great extent, an indirect process.
.
Drop-tracks,3 formed in an expansion chamber upon the ions
created by the
maybe observed by means of the
apparatus shown in gure 9—5. As the piston P is pui—led down,
the shutter S permits a narrow beam
of x-rays to pass through the waterFL !
i
'
C
-
_
saturatèd gas_ in the chamber ÏC. ‘
'
———' —_—ÎîîÎΗ—r
.
The droplets of
form
|
5
. 'FËË
'
on
the ions
then be seen
Frs. 9'_5_' A drop—track apparatus
are represented by the crooked lines.
_
_
used With
.
,
The total number Of ions produced
‘
'
a direct measure Ïof tHe strength
intensity of the x-ray
"
’
,
“
_
Since the ions are electrically
they may be
drawn over to
plates.
_
The jcurrent
which then ows
and maybe used
_
as a
This
the
_
most common methodofmeasurlng the1nten31 ty of“x—raysz It 'is,
of course,necessarythatsuiaentvoltagebeapplied
to the ioniza£
—
tion chamber—if‘1äläëstodrawoverawns before ahfy0fthem have
—
.
_
,
WiththensualtypeofchamberIngure9*Ôflsthe
10mzat10n "
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chamberThebrasswalls©fthecyhnderseweasoneeïectr0de '… i
andastw1reCsupp0rœd@fÏtheœnter©fthe°hamberbyan
: " Ï àî p- zi Â3‘ th1ncell®Phane@flummumwmd@wm@nendThegasmthe
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chambermYbederf0raf®natatm©sphecpressureThe
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