UPTAKE OF RADIOACTIVE NUCLIDES
LL
273
The extent of environmental contamination with world-wide fallout
varies both with latitude (since the majority of weapons trials have been in
the Northern Hemisphere) and with climate, since fallout is deposited
mainly, though not entirely, in rain. The internal dose from ingested radioactive materials is also influenced by agricultural factors and by the choice
of food. The evaluation of man’s exposure to radiation from fallout is
further complicated by the fact that whereas some components of the dose
ntific Committee on the Effects of
comprehensive estimate which has
yerienced by the world population.
, column 1.
om cosmic rays and from terrestrial
cay products of the uranium and
earth’s crust. It is of interest that
are received for a short period only, others will be,experienced for many
years. Accordingly it is appropriate to consider not only the annual ex-
the U.N. Report (2) is appreciably
til recently; this is because the sig-
od to a relatively constant radiation
posures which have been received hitherto, but also the continuing level to
which the population has been committed. Annual dose rates in the United
Kingdom in the middle of 1959 are shown in Table I, column 2. That time
organs. Thus, the major dose from
is selected because the highest exposures from the early series of weapons
trials were then experienced; the choice of the United Kingdom as an
cosmic rays has but lately become
ingested materials may vary widely
mainly to radium and its daughter
example rests partly on the availability of data and partly on the fact that
it lies in a latitudinal band of relatively high deposition, Table I, column 3,
based on. the U.N. Report (2), shows the estimated exposure of the world
sources to different tissues is esti-
er year.? Considerable variations in
population from weapons tests up to 1961, averaged over the years 1954 to
2000 AD; in column 4 of the table the fraction of the dose from these tests
-ent localities on the earth’s surface.
2, rises both with increasing altitude
which will not be received until after 2000 AD is shown.
e from the equator. The dose from
Iodine 131 is not considered in Table I, since the average exposure of
ust is subject to even greater varia-
the population gives little indication of its significance. This nuclide is of
be several times above the average
concern primarily as a source of exposure of infants who consume appreciable quantities of fresh milk, partly because of the very small size of their
ised by the choice of building matremely high background, values of
. The internal dose from the radium
thyroid glands in which it is concentrated, and partly because milk is usually
the most highly contaminated food. Doses to infants from iodine 131 have
on occasions been considerably higher than those from any other component
of fallout; for example, towards the end of 1961 it was estimated from the
of extra radiation which man has
eniently divided into those resulting
nent with the radioactive substances
itter group will be considered first;
t source. Estimates of the mean dose
‘+s where modern medical procedures
year in Norwayto 58 in France (2).
analysis of milk (5) that the thyroid glands of infants fed on fresh milk in
the United Kingdom would have received about 170 mrems (2).
Table I shows that the doses from fallout have hitherto been small relative to those from natural sources; they are less even than that from diagnostic radiology. However, since the present evidence indicates that all
exposure to radiation may be deleterious, these relatively small additions to
h sources as luminous watches, shoe-
man’s exposure cannot be ignored. Furthermore the possibility of signifi-
cantly higher levels of exposure in the future cannot be excluded. Nonethe-
: information on all aspects of man’s exannexes and bibliographies covering not
gactivity and the behaviour of radioactive
» existence of this document makes it unverage of the literature, except on topics
ration.
of radiation is usually measured in rems.
g the absorbed dose in rads (1 rad is 100
ye biological effectiveness) for the type of
d gammaradiation is 1, that for alpha and
I
Te pee Serye FE
less, the realization that past doses from fallout have been smaller than
those accepted unknowingly by persons who move from areas of low to higher
natural background, can aid a rational approach to new problems.
Ingested materials are the main sources of exposure from fallout and, of
these, strontium 90, caesium 137 and carbon 14 are the most important.
Carbon 14, though currently delivering relatively small doses, is, because of
its long half life (5570 years), a continuing source of exposure. The total
dose commitment from this nuclide released by past weaponstrials should
approximately equal that from all other sources of fallout (2).
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