Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
(251) The activity present in a wound can be detected with conventional detectors
if the contaminant emits energetic -rays. In the case of contamination with a-
emitting radionuclides, detection is much more difficult since the low energy X-rays
that follow the a-decay will be strongly attenuated in tissue; this effect is more
important the deeper the wound. It is often necessary to localise the active material
and this requires a well-collimated detector. Wound monitors must have an energy
discrimination capability if a good estimate is to be made of contamination with
mixtures of radionuclides. If whole body measurements are made, it may be necessary
to shield any activity remaining at the wound site.
(252) For activity calibrations of in vivo monitoring systems, laboratories generally
use physical phantoms, either commercially available or handcrafted (e.g. the Bottle-
Mannikin-ABsorption (BOMAB) phantom, the Lawrence Livermore thorax phantom
(Griffith et al, 1986; Snyder et al, 2010)). This approach has some limitations with
respect to the body size, body shape, and radionuclide distribution. The distribution of
the radionuclide in the calibration phantom should match that expected in the human
subject as far as possible. Alternatively, numerical calibration techniques may be
applied. Mathematical software combines voxel phantoms and Monte-Carlo statistical
simulations to model photon transport from the phantom and the detection of photons
by a simulated detector (Franck et al, 2003; Hunt et al, 2003; Kramer, 2005; Gómez-
Ros et al 2007; Lopez et al 2011a).
(253) The IAEA (1996) and the ICRU (2002a) have given guidance on the direct
measurement of body content of radionuclides.
4.3 Analysis of Excreta and Other Biological Materials
(254) Excreta monitoring programmes usually involve analysis of urine, although
faecal analysis may also be required if the material is relatively insoluble. Other
samples may be analyzed for specific investigations. Examples are the use of nose
blow or nasal smears as routine screening techniques.
(255) The collection of urine samples involves three considerations. Firstly, care
must be taken to avoid adventitious contamination of the sample. Secondly, it is
usually necessary to assess or estimate the total activity excreted in urine per unit time
from measurements on the sample provided. For most routine analyses, a 24 h
collection is preferred but, if this is not feasible, it must be recognised that smaller
samples may not be representative. Where a 24 h sample is not easily collected then
the first morning voiding is preferable for analysis (IAEA, 2000). Measurement of
creatinine concentration in urine has frequently been used to estimate 24 h excretion
of radionuclides from urine samples collected over part of a day. Tritium is an
exceptional case for which it is usual to take only a small sample and to relate the
measured activity concentration to the concentration in body water. Thirdly, the
volume required for analysis depends upon the sensitivity of the analytical technique.
For some radionuclides, adequate sensitivity can be achieved only by analysis of
several days’ excreta (e.g. Duke, 1998).
(256) The interpretation of faecal samples for routine monitoring involves
uncertainty owing to daily fluctuations in faecal excretion. Ideally, therefore,
collection should be over a period of several days. However, this may be difficult to
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