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Answer:
There is no transformation of CRs according to geometry or occupancy factors - these are used in determination of dose only. Occupancy factors influence external dose estimates only. However, perhaps the guidance within the ERICA Help is to some extent misleading as it suggests the user can use the occupancy factors to model organims which do not spend 100 % of their time in a given ecosystem. However, if for example an occupancy factor of 0.4 is used the external dose rate would be reduced to 40 % of that if the organism was assumed to spend 100 % of its time in the ecosystem under consideration, whereas, the internal dose estimation (and wholebody activity concentration) would be the same (as if the animal spend 100 % of time in the ecosystem).Note that the Area Factor (AF) parameter in RESRAD-BIOTA is used in the estimation of internal dose rate (although the report tissue activity concentration appears to stay the same regardless of the value of AF).

Answered by Nick Beresford 07/06/2010