secondly , the effect of variation of spatial sensitivity was studied by measuring the activation and detection efficiencies of small samples at many positions within an anthropomorphic phantom , and also by comparing the known amounts of nitrogen within a new type of phantom in which the elements are fixed , with the amounts measured using a calibration based on experiments with a bush phantom in which the elements are freely diffusible within each phantom part .
C0028158
nitrogen
C0013879
elements