MARMAD - Development of a model to determine the dose of radiation received by marine mammals

Lead Institute FI Institute of Fisheries Ecology

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Marine mammals accumulate radionuclides particularly strongly due to their long lifespan and their top position in the food chain. All studies conducted to date have been based on simplified dosimetric models with high uncertainties in dose estimation.
The development of modern dosimetric models (e.g. voxel models) is necessary in order to obtain a realistic and reliable estimate of the radiation dose for marine mammals. Thanks to modern diagnostic imaging methods, anatomical features are described in great detail in these models. The model can also be easily adapted to the body characteristics of the subject, thus increasing the accuracy of the dosimetric calculation.
Harbour porpoises are one of the four marine mammal species found in German waters and are very well suited as reference organisms for environmental health due to their similarity to other marine mammal species, their occurrence in the North and Baltic Seas and their local fidelity.

Background and Objective

The aim of this project is to develop a state-of-the-art computational model for a harbour porpoise (Phocoena phocoena) based on CT data. This model will be coupled with the Monte Carlo code MCNP to calculate dose conversion coefficients for internal and external exposures for nine energies between 0.1 and 4 MeV of gamma and beta particles. These conversion coefficients have the great advantage of being an essential tool in the event of an accidental release of radionuclides into the marine environment.

Approach

The tissues of dead porpoises are characterised non-destructively using computer tomography and a dosimetric tissue model is developed from this. This is coupled with the Monte Carlo code MCNP to calculate dose conversion coefficients for internal and external exposures for an energy range of gamma photons and beta particles from 0.1 to 4 MeV. These energy-dependent dose conversion coefficients can be used to calculate dose coefficients for any radionuclides, which enable rapid dose estimates for harbour porpoises after an accidental release of radioactive substances, for example. As the size and shape of harbour porpoises and their organs vary, the influence of these parameters on the internal and external dose is investigated using an uncertainty analysis.

Preliminary Results

The main result of this project is a model that allows an appropriate estimation of the dose conversion coefficients for the organs due to internal and external exposure for the most important artificial radionuclides. In addition, the influence of the activity distribution and the different body sizes and shapes of the various cetacean species on the dose estimation will be evaluated.
In this way, more accurate dose estimates can be made for the currently most important environmental contaminations with radioactive substances (e.g. Baltic Sea, Irish Sea) and guidelines for the selection of suitable protective measures for future accidental releases of radionuclides into the marine environment can be established.