For most typical radiological contamination situations involving the inhalation of
radioactive material, organ dose commitments are calculated using published inhalation dose conversion factors.
Inhalation dose conversion factors are available for
activity on particles of less than
10um
in diameter;
however, inhalation dose
conversion factors for large particles are not available in the published literature.
Accordingly, for the purpose of this dose calculation a set of large-particle inhalation
dose conversion factors is developed.
For particles greater than 10ywm diameter, essentially all of the inhaled material
is initially deposited in the nasal or nasopharyngeal region of the respiratory tract
(Reference 17).
This material is removed by chemical (absorption) and mechanical
processes, and goes either to the blood, with subsequent transfer to other body organs,
or to the gastrointestinal (GI) tract, with subsequent transfer to the blood and further
transfer to other body organs or bodily elimination by excretion.
The "pulmonary
clearance classification" of the inhaled material (roughly analogous to the solubility of
the material) determines the amount of the material that is initially transferred to the
blood or the GI tract; for example, 99 percent of an "insoluble" material will go to the
the GI tract with only | percent going to the blood, whereas a "very soluble" material
will be divided evenly between the GI tract and the blood (Reference 16).
As ingestion plays a major role in the fate of an inhaled large particle, the largeparticle inhalation dose conversion factors used for the present dose calculation are
Obtained by
modifying ingestion dose conversion factors.
This
modification
is
necessary to properly account for that portion of the inhaled materia! that is initially
transferred to the blood, rather than to the GI tract.
construct
large-particle’ inhalation
ORNL/NUREG/TM-190
radionuclides.
dose
(Reference 16)
for
The TM-190 dose conversion
The metabolic data needed to
conversion
the
most
factors
are
radiologically
given
in
significant
factors, based on the most current
dosimetry information, are used in conjunction with these. For those radionuclides not
addressed in TM-190, unmodified ingestion dose conversion factors are taken from
NUREG-0172 (Reference 18).
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