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Posted: 24/02/2012
From:
Chantal Medri
Canada

Dose

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rate equation

Question:

I am looking for the dose rate equation used by ERICA which takes into account the media. For instance, for the aquatic organism, I expect that the calculated dose rate should look something like this:

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Furthermore, are the DCCs for water and sediment the same? Sediment is denser than water, so I expected that different DCCs should be used.

Answer:

Your equation is the correct representation of the calculation of total EXTERNAL dose rate. This does not appear to be in documentation although equations for individual elements of dose (e.g. external from sediment at the sediment interface etc.) are presented in the Help file and Brown et al. 2008 paper.

You are also correct in that typical wet sediment densities tend to be greater than those for water but this difference isn't normally huge especially where the porosity, and therefore the water content, is high. In some cases you may get a factor of 2 to 3 difference between wet sediment and water but in view of all the other uncertainties this is fairly minor. For sake of simplicity using the same DCC for water and sediment isn't such a poor approximation and it gets around the problem of having to decide on an arbitrary reference density for wet sediment.

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