Measuring terrestrial wildlife external radiation exposure under field conditions

This thesis presents the results of a 3-year project to develop methods for measuring external radiation exposure of free-ranging terrestrial animals under field conditions. An evaluation of available passive dosimeter technologies was undertaken and guidance developed on the selection of dosimeters for different sizes of terrestrial animals. To test dosimeters under field conditions, a field study using reindeer in an area of Norway with elevated 137Cs was initiated. The dosimeter selection guidance was used to identify four passive dosimeters (i.e. TLD, OSLD, RPLD and DIS), which should be suitable for reindeer. To protect these dosimeters during use, they were housed in an aluminium box that could be attached to a collar around the reindeer’s neck. The performance of dosimeters within the box was tested in a laboratory. This testing confirmed dose linearity, angular linearity for the angles tested (45˚ – 135˚) and energy linearity for radionuclides tested (137Cs, 60Co, 226Ra). The dosimeter box did not respond to beta exposure. The external absorbed doses of a reindeer herd (Vågå, Norway) were measured over 11 months using the dosimeter box developed. Dosimeter results were then compared with model predictions. There was a significant difference between the estimates of dosimeters, but the difference of the mean doses between maximum and minimum values was <14 %. Reindeer external doses were modelled based on GPS tracking data and data on radiation in their environment. The mean predicted doses using the GPS tracking data were not significantly different to RPLD and DIS. However, the TLD and OSLD results were 18% higher than the mean dose estimated using the reindeer GPS tracking data. Average external doses predicted across the herd area (without using GPS data) were significantly lower than doses from all dosimeter types and predicted using the GPS data because the animals favoured the more contaminated areas of the study site which were good grazing in several seasons for those reindeer. A deer dosimetry phantom was created from red deer CT images and a human adult dosimetry phantom to estimate a whole-body dose and organ doses from external radiation exposure. The data of whole-body and organ doses from x-ray and 137Cs were used to calculate conversion factors that can be used to convert from external whole-organism doses of deer species to individual organ doses from external exposure