[Vou. 91
1 therefore
e daughter
ent of soils
1? curies of
ms of most
neous rock
il respects.
rranite. Its
Rubidium,
andanee in
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1964]
.WARTIN : RADIOECOLOGY AND STUDY OF ENVIRONMENTAL RADIATION
287
ingested with food and water or other nonliving materials. According to
Hursh (1955), the most important natural radionuclides assimilated by
man are C-14 and K-40 (Table 4).
According to Libby (1955) and others, people who live between sea
level and an altitude of 5000 feet above sea level in areas underlain by
granite are normally exposed to about 200 mr/year of ionizing radiation
from natural sources. Roughly 25% of this total is due to cosmic radiation,
50¢e to external emitters, and 25% to internal emitters.
b. ‘‘Man-made’’ sources. The major man-made sources of ionizing radiation in the biosphere are radionuclides produced by atomic fission or by
neutron induction and released to the atmosphere as reactor effluents or as
fallout from nuclear weaponstests.
Table 3. Estimated activity of naturally oceurring radionuclides in the above ground
parts of an acre of green crop plants weighing 50 tons*.
Radio-
Activity in
Radio-
Activity in
which are
nuclides
euries x 10-9
nucildes
curies x 10-9
[In soil, for
K-40
Rhb-87
C-14
75,600
19,900
13,500
Ra-226
U-238
H-3
400
157
156
sea water
m in fresh
123 x 104
31.0 x 10738
156). Since
L957), this
e acre-foot
water.
are readily
id H-3 are
d C-14 in
itration of
ve ground
tain about
g only the
ratlo on a
‘le erop of
soil.*
ym the at-
ionuelides
erived from
* From: Fried & Heald (1959).
Table 4. Estimated activity of naturally oecurring radionuclides in a man weighing
70 kilograms".
Radio-
Activity in
Radio-
Activity in
nuclides
euries x 10-12
nuclides
curies x 10-12
K-40
C-14
190,000
85,000
Ra-266
H-3
100 to 290
6.3 to 31.5
* After: Hursh (1955),
The direct effects of neutron and gamma radiation associated with the
operation of a nuclear reactor are largely confined to the immediate vicinity
of the reactor. Reactor effluents containing small quantities of fission products and radionuclides produced by neutron induction may be released to
environmental media, but only local areas are affected. The disposal of
highly radioactive reactor waste products is usually aeeomplished in a
manner which prevents their release to the environment.
The direct effects of neutron and other ‘‘prompt’’ radiation released by
the detonation of nuclear weapons are usually confined to areas in which
the effects of blast and thermal radiation are more important. The radionuclides produced by nuclear detonations in the atmosphere are—by
virtue of their quantity, world-wide distribution, and potential biological
significance—the most important man-made sources of radioactivity in the
biosphere.
The slow fission of uranium produces at least 170 isotopes of 35 lighter