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MITHOD
13
Mesothorium in living persons can be detected in far smaller amounts by the
expired air method than radium, as will be explained in Part II of this report
dealing with the underlying principles upon thich these measurements are based.
Here let it suffice to say that we had no difficulty in establishing the presence
of mesothorium in Subject O, whose total gamma ray activity was scarcely 5 micro-
grams expressed as radium equivalente Since this subject had handled consider~
ably more radium than mesothorium it is reasonable to assume that the principal
source of the gramma radiation was radium.
To establish the presence of mesothorium (or radiothorium), the expired air
is tested for thorium emanation (thoron). The air as it is expired is blown
directly into the ionization chamber set up with electroscope head in position.
The natural drift having been read, the dried, filtered current of expired air
is blown through the chamber for a minute or two. Readings of drift are then
taken at once at intervals of 54.5 seconds by two observers. One makes the
readings as the other observer holding two stop watches calls off the intervals of
54.5 seconds. When the first reading is being taken the timer starts one of the
stop watches; the drift observer makes the second reading at the moment the timer
indicates that 54.5 seconds have passed. The timer also stops the watch at 54.5
seconds and starts the other watch at the same time.
The reader makes his third reading
the instant the timer calls the second period of 54.5 seconds, and starts the other
watch off on the third half value interval, etc. An example of the readings
actually recorded by the timer when Subject C. Table IV was under test follows:
TABLE IV.
TEST FOR THORIUM EMANATION
Interval : Scale Readings se Gross drift Division per Interval: Net drift per interval
1
: 92 - 67
:
25.0
:
21.7
2
:
67 - 53.5
:
13.5
:
10.2
3
:
53.5 A 45.2
:
8.3
:
5.0
4
:
45.2 - 39.6
:
5.6
:
2.3
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"ocrText": "-11-\nMITHOD\n13\nMesothorium in living persons can be detected in far smaller amounts by the\nexpired air method than radium, as will be explained in Part II of this report\ndealing with the underlying principles upon thich these measurements are based.\nHere let it suffice to say that we had no difficulty in establishing the presence\nof mesothorium in Subject O, whose total gamma ray activity was scarcely 5 micro-\ngrams expressed as radium equivalente Since this subject had handled consider~\nably more radium than mesothorium it is reasonable to assume that the principal\nsource of the gramma radiation was radium.\nTo establish the presence of mesothorium (or radiothorium), the expired air\nis tested for thorium emanation (thoron). The air as it is expired is blown\ndirectly into the ionization chamber set up with electroscope head in position.\nThe natural drift having been read, the dried, filtered current of expired air\nis blown through the chamber for a minute or two. Readings of drift are then\ntaken at once at intervals of 54.5 seconds by two observers. One makes the\nreadings as the other observer holding two stop watches calls off the intervals of\n54.5 seconds. When the first reading is being taken the timer starts one of the\nstop watches; the drift observer makes the second reading at the moment the timer\nindicates that 54.5 seconds have passed. The timer also stops the watch at 54.5\nseconds and starts the other watch at the same time.\nThe reader makes his third reading\nthe instant the timer calls the second period of 54.5 seconds, and starts the other\nwatch off on the third half value interval, etc. An example of the readings\nactually recorded by the timer when Subject C. Table IV was under test follows:\nTABLE IV.\nTEST FOR THORIUM EMANATION\nInterval : Scale Readings se Gross drift Division per Interval: Net drift per interval\n1\n: 92 - 67\n:\n25.0\n:\n21.7\n2\n:\n67 - 53.5\n:\n13.5\n:\n10.2\n3\n:\n53.5 A 45.2\n:\n8.3\n:\n5.0\n4\n:\n45.2 - 39.6\n:\n5.6\n:\n2.3"
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