Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
Publication 70 (ICRP, 1995b) and revised systemic biokinetic models for selected
isotopes of 31 elements given in Publications 56, 67, 69 and 71 (ICRP, 1989, 1993b,
1995a,c). Biokinetic models for other elements were taken from Publication 30 and
modified by addition of explicit excretion pathways to improve dose estimates for the
urinary bladder and colon walls. Publication 68 did not give ALIs, as ICRP wished to
emphasise the need to take account of all exposures to ionising radiation in the
workplace, from external radiation and intakes of all radionuclides.
(23) Publications 54 and 78 gave guidance on the design of monitoring
programmes and the interpretation of results to estimate doses to workers following
radionuclide inhalation or ingestion (ICRP, 1988a, 1997b). The guidance was
supported by numerical data to enable the assessment of intakes and doses from
bioassay data (that is, measurements of body and organ content, and daily urinary and
faecal excretion). These data were provided for a number of radionuclides selected as
those most likely to be encountered in the workplace. Predicted values of the
measured quantities for various times after a single intake or for routine monitoring
were given in terms of the activity of the intake per unit activity measured. Standard
dose coefficients would then be used to calculate effective dose from the assessed
intake.
1.4 Changes in Publication 103 (ICRP, 2007) that affect the calculation of
equivalent and effective dose
(24) In the 2007 Recommendations issued in Publication 103 (ICRP, 2007), the
concept and use of equivalent and effective dose remain unchanged, but a number of
revisions were made to the methods used in their calculation. Changes were
introduced in the radiation and tissue weighting factors, from the values previously
recommended in Publication 60 (ICRP, 1991). Since radiation weighting factors (wR)
for photons, electron and alpha particles are unchanged, the only difference of
potential importance to internally deposited radionuclides is for neutrons (Table 1).
The changes made do not reflect the availability of additional data but rather a
reconsideration of the appropriate treatment of radiation weighting for protection
purposes. The abandonment of a step function for neutron wR as a function of energy
is a reflection of the fact that in practice only a continuous function has been used.
The major change in the continuous function is a lower wR value at low energies
which more properly reflects the low LET contribution from secondary photons. In
addition, there are good theoretical reasons for assuming that wR values at high
energies will converge with that for protons.
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