Health Physics

estimate” values are needed to calculate realistic
population-average or typical mdividual doses
The purpose of this paper 1s to (a) review and
evaluate historical data on the physical and chemical
characteristics of radionuclides associated with fallout
debris includmg fractionation, solubility, and other fac-

tors which may affect the1r absorption by humans, (b)
review and evaluate f, values for key fallout radionuchdes from the available hterature as they pertain to
fallout m general and to the unique coral environment
of the Marshall Islands, mm particular, and (c) provide

an evaluation and present our “best estimates” for f,
values for use im reconstruction of realistic mternal
doses from acute imtake of local and regional fallout

from nuclear tests, and for chronic intake of radioac-

tive materials following their mcorporation ito terrestrial and aquatic foodstuffs In this paper, local
fallout 1s assumed to have occurred at close-in locations that are typically associated with large particle
sizes (250 jum) and extend roughly up to 300 km from
ground zero, whereas regional fallout that occurs at
distant locations 1s composed of only smaller particle
sizes and 1s assumed to extend from 300 to 3,000 km

from ground zero
Justifications for the choice of f, values for fallout
radionuclides were made takmg mto account the particular circumstances of various nuclear test conditions and
the expected nuchdes’ solubility and biological availabil-

August 2010, Volume 99, Number 2
Unique characteristics of the Pacific
Proving Ground
The basic components of topsoil at coral atolls lke
the Marshall Islands are coral-based sand, hard and
weathered coral, and marme shells Coral-based soil 1s

typically low m organic matter, potassium, clay, and
many other nutrients, but ennched m lime (CaCO,)
content (Srmon et al 2002)

In the case of detonations over coral or coral-based
soils, calc1um carbonate m the ground is heated to very
high temperatures or completely vaporized, resultmg m
the formation of relatively fme particles When such
particles mix with bomb debris m the cooling fireball,
they adsorb fission radionuchdes within and on the
surface of particles (Norman 1973) Fresh coral debris 1s
largely CaO, CaCO,, and Ca(OH), (Herdt et al 1953,
Maxwell et al 1955) and, hence, raises the pH considerably (pH 10-11) when it dissolves m water (Crocker et

al 1965) The maximum soil adsorption and retention of
Sr, Cs, Y, Ce, and Pu also occurs at this high pH range
In addition, me rich soil may further mcrease the
retention of Sr and Cs (NAS 1963) In fallout particles

from water-surface tests, radioactivity 1s carned m water
droplets which form a cloud of mustafter detonation In
the presence of sea water, some fission products may be
fused in sodium oxide particles or precipitated as sulfate

ity, whenever such mformation was available Informa-

on particle surfaces (discussed im detail later) For tests
conducted on barges or towers, iron from the steel

review of the available fallout hterature, declassified

mixed iron, calcium, and fission-products oxides (Adams

tion presented m this paper resulted from a thorough
government documents, and various reports from national and mternational orgamzations Although emphasis wasgiven to nuclear weapons testmg conductedat the
Marshall Islands, mformation provided here may be
applicable to fallout from tests or detonations conducted
A large numberof fission and activation products
are formed m nuclear weapons tests (Hicks 1981) Most

of them are either produced m low yield or have short
half-lives Key fallout radionuclides that contribute substantially to the mternal dose to humans resulting from
nuclear tests conducted m the Marshall] Islands are
isotopes of iodine (I), tellunum (Te), cestum (Cs),
strontium (Sr), yttrum (Y), molybdenum (Mo) barium
(Ba), lanthanum (La), cerium (Ce), praseodymium (Pr),
iron (Fe), cobalt (Co), zme (Zn), and neptuntum (Np)
(Simon et al 2010) Plutomum (Pu), americ1um (Am),
uramum (U), zirconum (Zr), ruthemum (Ru), rubidium
(Rb), and bismuth (B1) are among other elements of

terest present in radioactive fallout Review and evaluation of f, values for the above elements from exposure
to fallout are addressed im this document

structures can mcorporate m fallout particles to form
et al 1958) Small fallout particles from coral islands
were found to be 10-50% water soluble and almost
completely soluble m acids (Cohn et al 1954, Herdtet al
1953, and personal experience)

Fractionation, solubility, and bioavailability of
fallout debris
Fractionation and solubility of fallout debris are
important phenomena because of their relationship to
bioavailabihty and the absorption of various radioactive
species by humans The fractionation occurs due to both
physical and chemical separation of fallout particles
and/or fission products The degree of fractionation 1s a
function of many mteracting factors mcludmg the physical and chemical properties of nuchdes formed m the
fission process as well as those of progeny elements ma
given decay cham, particle size and composition, distance from ground zero, the specific conditions of nuclear detonation (weapon composition, yield, burst
height, meteorological conditions, etc ), and the propertes of the surroundmg environment after the deposition
of fallout particles (Tompkins and Wermer 1955, Beck

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