Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
E(50) = I x e(50) = M x e(50)/m(t)…………(7.2)
If the time of the intake during a monitoring period is unknown, the intake is
generally assumed to have occurred at the mid-point of the period (Section 6.3).
(412) Dose per unit content, z(t), represents the committed effective dose per unit
organ (body) radionuclide content or per unit radionuclide content in the 24 hour
excreta sample at time t after an acute intake. The use of z(t) simplifies the dose
evaluation to a single step, instead of the traditional method of first applying the
retention or excretion function m(t) to calculate the intake (equation 7.1), and then the
dose coefficient e(50) to calculate the resulting effective dose (equation 7.2).
E(50) = M x z(t) ………………………(7.3)
(413) Values of dose per unit content, z(t), are provided to allow a more
straightforward assessment of committed dose from bioassay measurements without
the need to first determine the intake. For measurements of activity in body tissues
and excreta, predicted values of committed effective dose are tabulated for various
times after radionuclide intake following inhalation, ingestion, entry through wounds
or uptake to blood.
(414) Graphs of predicted activity of the radionuclide in selected body tissues, urine
(daily excretion) and faeces (daily excretion), at various times after intake, are given
for an acute intake of 1 Bq of the radionuclide (unit intake). These values correspond
to m(t). Figures are given for intakes by inhalation, ingestion, and direct transfer to
blood. Data are given in the form of fractional activity related to the intake, i.e. Bq per
Bq intake for retention and daily excretion. One exception to this is for intake of
tritiated water where data are given in Bq l -1 per Bq intake since this is directly related
to the dose rate.
(415) Data are given for time periods up to 10 4 days after intake or until the
fractional activity is less than 10 -10 of the intake.
(416) For each radionuclide, the monitoring periods have been selected (as in
Publication 78, paragraph 91) for intake by inhalation for all absorption Types so that
any underestimation introduced by an unknown time of intake is no more than a factor
of three when an acute intake in the middle of the monitoring interval is assumed. The
frequency of monitoring, determined using the models that have been applied, is
determined both by the behaviour of the radionuclide in the body and its physical
half-life. Within any workplace, the probability of occurrence of an intake should also
be taken into account.
(417) The accompanying CD-ROM gives extensive additional information for all
relevant isotopes of each element, including:
Committed effective dose (Sv) per unit measurement (Bq) for an acute intake
by inhalation of aerosols with median sizes ranging from an AMTD of 0.001
µm to an AMAD of 20 µm;
Committed effective dose (Sv) per unit measurement (Bq) for an acute intake
by ingestion, with default fA values appropriate for the element;
Bioassay data (i.e. whole body and/or organ retention, and daily urinary and
faecal excretion, Bq per Bq intake), for an acute intake by inhalation of
aerosols with median sizes ranging from an AMTD of 0.001 µm to an AMAD
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