254
11.
SPONTANEOÜS DISINTEGRATION
»
-
.
per
cent of the total equilibrium amount
of gas Will be formed
and in 3 weeks there Will be 99 per
cent.
The tube is then con—
nected to an emanation electroscope and heated to drive out the
emanation.
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.
EXPERIMENT 11—1
THE INTENSITY OF RADIOACTIVE SUBSTAN CES
Read the discussion of electroscopes given in chapter 17.
_
The active material, in a shallow metal tray, is placed in the
electrosCope. Since the alpha rays are easily absorbed, only the
surface layers contribute to the activity and the thickness of
the material in the pan
is unimportant unleSs the layer is very
thin.
However, some of the activity is due to beta rays which are
not so
easily absorbed in passing through the material itself.
Therefore, use equal weights, or roughly, use equal thicknesses
(1 mm.) of the various materials (spread evenly in shalloW metal
pans about 6 cm. in diameter).
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.
Experiment.—Compare the intensities of at least three substances such as uranium oxide, pitchblende, thorium nitrate, etc.,
taking the average of four determinations for each. If a standard
is available, express the activities in milligrams of radium; if not,
express in terms of one of them, say the pitchblende.
[
Measure the capacity of the leaf“ system and compute the
ionization current in amperes produced by the standard substance.
Also compute the number of ions which it producesper
second per square centimeter.
;
_
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;
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EXPERIMENT 11—2_
1
'
RATE on FORMATION OF THORIUM (:
«. dppamtus—Rædthedxscusswnnelectrosœpea m chap
15°°nnedt°the °upbya ghtttmg bakehte C°V€fThc