A study of the absorption of vitamin B12labelled with57Co was performedby whole-body counting. The subjects were measured in prone and supine positionsby a NaI(Tl) scintillation detector which moved l50 cm along the subject. Thetechnique was evaluated by model studies, by whole-body counting of subjects and byradioactivity assay of excreta. The influence of body size upon the whole-bodycounter sensitivity was demonstrated. This influence was considerably diminishedwhen the Compton energy range instead of the photopeak energy range was used forthe determination of the radioactivity in the body.
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