150
INTERNAL DOSE FROM SHORT-LIVED RADIONUCLIDES
THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
Therefore, most of the absorbed dose (in ergs/g
or rad units) is delivered to the lower large
intestine in the case of the radionuclides with
relatively long half-lives which are listed in the
ICRP Handbook. The material spends 1
hour in the stomach, 4 hours in the small in-
were given for 5 different sets of assumptions:
ble radioactive material is inhaled with the lung
testine, 8 hours in the upper large intestine, and
18 hours in the lower large intestine. Jf
radionuclides of shorter half-life are considered
in future publications and if MPC values are
as the critical body organ; and 5. Insoluble
radioactive material is inhaled with various
portions of the G.I. tract to become the critical
only the lowest maximum permissible values
are listed in Table I, The three assumed permissible exposures were 0.3 rem/wk, 15.7
rem/yr or 150 rem/70 years following the
exposure, We should note that in Tables I
and JI the 0.3 rem/wk is the limiting case-—
givenfor single exposure, we may expect other
body tissue.
In the present ICRP Handbook
the assumption is made that the fraction, f,,
of the radionuclide passes through the small
intestine into the blood so that only (1—f,)
reaches the upper and lower large intestine.
Therefore, if radionuclides are considered in
which f,2x1, the critical organs are unlikely
to be the large intestines.
Although no official MPC or q values for a
short period of single exposure have been
agreed upon, unofficial single exposure values
have been adopted by some of the laboratories
working with certain of the radionuclides in
order (o aid in assessing the hazards associated
with accidents or “spills.” Previous attempts
have been made to prepare tables of MPC
values for single exposure. Tables of MPC.
values of some 80 radionuclides were given for
two cases: 1. The radionuclide is taken into
the body by inhalation or ingestion over a
portions of the G.I. tract as the critical body
organ. The calculations were made for three
criteria relative (o permissible exposure and
gives the smallest maximum permissible
values—with the exception of 5 bone-seeking
radionuelides (Sr°+Y®, Sm’, Ra’, natural
thorium, and Pu™) in the soluble form. Jn
these cases, 150 rem/70 years is the limiting
case. In the case of a wound contaminated
with insoluble radioactive material it was
assumed that all the contamination remained
in 1 mg of tissue at the wound site. In the
cases of inhalation of radioactive material, the
we values given in Tables 1 and IT correspond
to the amount of the radionuclides initially
present in the air—for example, as the result of
an accident—which if inhaled over a period of
24-hour period,‘ and 2. The radionuclide is
8 hours would deliver the indicated dose. The
radioactive material decays with a half-life T,
over an 8-hourperiod, or by way of a con-
tion, and is eliminated with a biological. half-
taken into the body by inhalation or ingestion
taminated wound. None of these single exposure values hasofficial status.
Itis to be expected that single exposure values
will be included in the Internal Dose Handhooks in the near future. Table I is a summary of the single exposure data given at the
Conference on Peaceful Uses of Atomic Energy
in 1955 at Geneva‘.
Single exposure values
4 Morgan, K. 2. and M. BR Ford, “Developments im Internal Dose
Determinations,” Nucteonica, Vol. 12, Ne 4, $2 Qune 10541,
§ Morgan, K. 2, W. 8. Snyder, and M. R. Ford, “Maximum Per-
migsibla Concentration of Radlonuclides in Air and Water for Short
Period Exposure,” International Conference nn the Peaeeful Uses of
Atomic Enagy, Geneva, Switzerland(1054).
Single Exposure Values for Radionuclides for Tohalation and for Cantaminated Wounds
1. Soluble radioactive material is inhaled;
2. A wound is contaminated with soluble radio-
active material; 3. A wound is contaminated
with insoluble radioactive material; 4. Insolu-
in this period, i. e., both before and after inhalalife T, while in the body.
In the case of a
wound all the radioactive contamination enters
the wound at time zero. Values were not given
in the Geneva paper for ingestion because
experience had indicated that in cases of single
exposure, inhalation in general presents a much
greater hazard than ingestion.
However, in
some accident eases one may be concerned with
the ingestion problem and so Table IT is added
to give the uc that are considered permissible
to ingest in an 8-hour period, Tables I and IT
list values of ue present initially at the time of
ap accident, e. g., spill, explosion, failure of a
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