Occupational Intakes of Radionuclides Part 1 - ICRP

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convention and are not subject to uncertainty.
DRAFT REPORT FOR CONSULTATION
(355) It follows that there is no requirement to assess or record the uncertainty
associated with an individual dose assessment performed to demonstrate compliance
with regulatory requirements. Nevertheless, the assessment of uncertainties associated
with a specified monitoring procedure (including the dose assessment procedure)
provides important information for optimising the design of a monitoring programme
(Etherington et al, 2004a; Etherington et al, 2004b; ISO, 2011). Where uncertainties
in assessed effective dose are evaluated, uncertainties in material-specific model
parameter values should be considered, but individual-specific model parameter
values should be taken to be fixed at their reference values (Section 6.1).
(356) This section describes and discusses the important sources of uncertainty in
retrospective assessments of dose. The uncertainty in an internal dose assessment
based on bioassay data depends on the uncertainties associated with measurements
used to determine the activity of a radionuclide in vivo or in a biological sample,
uncertainties in the exposure scenario used to interpret the bioassay results, and
uncertainties in the biokinetic and dosimetric models used to interpret the bioassay
results. The exposure scenario includes factors such as the route of intake, the time
pattern of intake, the specific radionuclide(s) taken into the body, and the chemical
and physical form of the deposited radionuclide(s).
6.5.1 Uncertainties in Measurements
(357) Uncertainties in measurements of activity in the body or in biological samples
have been discussed in IAEA publications (IAEA, 1996a, 2000). There are no
standard procedures for indirect or direct bioassay measurements, although some
examples of bioassay methods are given in these reports and elsewhere. The choice of
the procedure, detector or facility will depend on the specific needs such as the
nuclides of interest, minimum detectable activities, and budget. All procedures used
to quantify the activity of a radionuclide are sources of both random and systematic
errors. Uncertainties in measurements are typically due mainly to counting statistics,
validity of the calibration procedures, possible contamination of the source or the
measurement system, and random fluctuations in background. A committee of the
U.S. National Council on Radiation Protection and Measurements (NCRP) has
developed a comprehensive report on uncertainties in internal radiation dose
assessment that addresses measurement uncertainties in great detail (NCRP, 2010).
(358) The total uncertainty associated with a measurement is generally expressed as
an interval within which the value of the measure and is believed to lie with a
specified level of confidence (EURACHEM/CITAC, 2000). In estimating the overall
uncertainty in a measurement, it may be necessary to take each source of uncertainty
and treat it separately to obtain the contribution from that source. Each of the separate
contributions to uncertainty is referred to as an uncertainty component.
(359) The components of uncertainty in a quantity may be divided into two main
categories referred to as Type A and Type B uncertainties (BIPM et al, 2010;
EURACHEM/CITAC, 2000; Cox and Harris, 2004; NCRP, 2010). Essentially, a
Type A component is one that is evaluated by a statistical analysis of the variability in
a set of observations, and a Type B component is one that is evaluated by other
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