Dose Coefficients for External Exposures to Environmental Sources

Draft document: Dose Coefficients for External Exposures to Environmental Sources
Submitted by Alex Malins, Japan Atomic Energy Agency
Commenting as an individual

General Comments

- Introduction paras 6-8: For ground contamination, the focus of the report is on external exposures from radionuclides distributed in soil. Some might be a little confused as to why the ICRP suggests this in general is the most important case. E.g. para 8: "Soil contamination is the most important source in large-scale accidents...". This is almost certainly not true for residents in large parts of Fukushima City, where it is a struggle to find any patches of soil in and amongst all the concrete and asphalt! The most important sources in that case will be contamination on asphalt, buildings and other urban surfaces.

An improvement in this respect would be to clarify that the photon dose coefficients derived for soil contamination in this report can also be applied, for radiation protection purposes, when assessing external doses from other ground types. This requires appropriate matching of the mass per unit area of the contamination depth profiles between the different cases, as per the discussion in sections 8.1.1 and 8.1.2. A caveat applies for low energy photons (<200 keV), where the mass attenuation coefficients are more sensitive to the elemental composition of the ground material (Saito and Jacob, 1995; Cresswell and Sanderson, 2012). It would also be helpful to quote ICRU (1994) who suggested an exponential distribution with relaxation mass per unit area of 0.1 g cm^-2 as an appropriate depth profile for low permeability urban surfaces.

- Effect of phantom orientation: related to the discussion in para 71 on the air submersion case, I think it would be helpful to add some comment on the effect of phantom orientation for the soil contamination case. I think it is worth citing the Saito et al. (1998) result that, given a plane source in the ground, effective dose is lower when the phantom is lying down compared to standing up. This result helps support the assumption for using upright phantoms for the soil contamination calculations in this report. Many will find this result counter-intuitive, as air kerma and H*(10) both increase towards the ground, but E is lower when the phantom is lying closer to the ground than when it is standing up!

Editorial Comments

- L658: “Absorbed dose D is used to set limits on organ/tissue doses to prevent tissue reactions (deterministic effects).” Some confusion here as this is being consulted on as a plan for the future, but currently ICRP sets dose limits to prevent tissue reactions using equivalent dose.

- L762: Expand acronym.

- L992: Malins et al. (2015) rather than Malins et al. (2016) contains the data appropriate to this sentence.

- L1128-9: Shouldn’t this say “the dose rate coefficient per air kerma decreases with increasing humidity”?

- L1130-1: “those mentioned above”. Details on the number of histories etc. for the soil contamination case are not mentioned until later on in the report (in Para 98).

- L1202/1215: Is Cinelli et al. (2018) a more appropriate reference than the EURDEP website?

- L1244: Surplus or missing bracket.

- L1479: “Fig. 5.5 (right)” -> “The right side of Fig. 5.5” or suchlike is better? The former had me looking for Fig. 5.5 on the same page as L1479.

- L2657-8: In terms of readability, it might be better to state the full 2.137 and 1.775 mm figures here. I was confused as to where 2.1 and 1.7 mm had come from on first pass reading.

- L2715-8: It might be worth highlighting this limitation somewhere in the main text of the report. And likewise that the effective dose coefficients of this report are not generally applicable for calculating equivalent dose to the lens of the eye, or to the hands and feet, which are the other tissues that the ICRP explicitly sets separate limits for.

- L2729: “photon”->”electron”

- L2786: “above 0.2 to 0.6 MeV” is slightly confusing. Why not simply write “above ~0.2” or whichever figure in the 0.2-0.6 MeV range is most appropriate?

- L2791: “EGS4” should be “EGSnrc”?


Cinelli et al. 2018. Digital version of the European Atlas of natural radiation. J. Environ. Radioact. In press.

Cresswell, A.J., Sanderson, D.C.W., 2012. Evaluating airborne and ground based gamma spectrometry methods for detecting particulate radioactivity in the environment: a case study of Irish Sea beaches. Sci. Total Environ. 437, 285?296

Malins et al. 2015. Fields of View for Environmental Radioactivity. Proceedings of the International Symposium on Radiological Issues for Fukushima's Revitalized Future. 28-34.'15_Proceedings_EN.pdf

Finally many thanks to all the authors of this report for the hundreds of hours of effort it must have taken to produce all the dose coefficients.