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45
been reflected in an increase in body burdensof
some radionuclides. As will be shown, the in-
creases, though manyfold, have remainedfar below maximum permissible levels.
ESTIMATION OF THE INTERNAL
RADIATION HAZARD
The potential radiation effects that may be pro-
duced byspecific quantities of internally-deposited
radioisotopes can be only roughly predicted from
so low thatlittle effort was made to quantify these
elements in the Marshallese until whole-body
counting techniques madeitfeasible.
The body burden of fission products can be
determined in three ways. The method ofchoice
is the direct zn vivo measurement by whole-body
spectrometry. The limitations of this method are
that few whole-body counters are in existence,
they require enormously bulky shielding and thus
are not easily transported to varioussites, and
their absolute calibration is difficult. Further,this
ternally-deposited radium. These effects do not
appear until a period of years (10 to 15) has
elapsed. Thus, althoughit is possible to estimate
method is restricted to analysis of gamma-emitting
isotopes, since, to date, a whole-body beta counter
has not been developed.
A second methodfor calculating body burden,
particularly for counting beta emitters such as
Sr°°, is the estimation of the internal deposition
within a few years after contamination yield no
data on the degree of damagethat mayultimately
the urine.
clinically observed effects of known amounts ofin-
the potential hazard in termsof the concentration
of internal emitters, clinical observations made
be produced.
In evaluating the long-term effects produced by
an acute internal exposure and exposure toresid-
from data obtained by radiochemicalanalysis of
Finally, it is possible to make a completely indirect estimate of the human body burden of
radioisotopes by what maybe called theenviron- .
ual contamination, Sr’? is clearly the criticalele-
mental approach. In this method, the estimate of
lese, and thusto estimate the body burdens.
the fission products present in the environment,
chiefly the soil and the important components of
ment. Particular effort was therefore made to
determine its levels in the urine of the MarshalOf the gamma-emittingfission products, Cs'*" is
the body burden is based on the concentrations of
the diet. In order to makethis estimate, data must
of the two radioelements are nearly equal, they
be obtained on the transfer of the fission products
between successive elements of the ecological
chain leading from soil to bone. For example, although Sr and Ca are chemically similar and thus
appear together in the various componentsof the
ecological chain, Ca is taken up preferentially by
plants and animals so thatit is necessary to deter-
duced radioelement Zn*, even thoughit, too, does
the concentration of a radionuclide in man from
its concentration in any step of the ecological
chain.
All three of these approaches to the estimation
of the body burdensin the Marshallese people will
be considered in this report.
of the greatest interest, even thoughit is of minor
significance as an internal radiation hazard. Like
Sr*’, Cs'3" has a gaseous precursor with a half-life
sufficiently long to avoid early condensation in the
fireball. Cs'** thus follows Sr*® into the stratosphere. Since thefission yields and the half-lives
are presentin thefallout in like quantities. While
they have different ecological cycles because of
their different chemical properties, Cs'?’ nevertheless provides a useful tracer for studying the movement of Sr°° through the biosphere, since its gamma-emitting properties makeit readily detectable.
Thereis also someinterest in the neutron-innot appearin levels hazardous to humanbeings.
The interest centers chiefly around the fact thatit
is definitely transmitted through marinelife, and
thus provides a clear example of the transmission
of a radioelement through the food chain to man.
Other fission products and neutron-induced
minethe discrimination factor for each step. When
these factors are known, it is possible to estimate
EXPERIMENTAL PROCEDURES
Whole-Body Counting
The gamma-ray activity from the internally-
Zr°°-Nb**, and Ru'®*-Rh**) also appear in small
deposited fission products and the neutron-inducedactivities in 227 of the Marshallese people
were measured with a whole-body gammascin-
may appearultimately in man,but the levels are
gamma-ray measurement of human beings was
activities
(Fe®5°°,
Co57-58.80,
Mn**,
Ce!**_ Pris,
amountsin thesoil and the food chain, and thus
tillation spectrometer. The techniqueof in vivo