THE BIOLOGICAL DIFFERENTIATION OF 99Mo AND 99Tcm IN RABBITS AND ITS EFFECT ON THE GAMMA-COUNTING RATE OF PLASMA SAMPLES

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Abstract
Thirty-one rabbits were each injected intravenously with 250-450 [mu]curies molybdate-99Mo in transient equilibrium with 99Tcm. Blood samples were taken at intervals from 0. 5 to 48 hours after the isotope injections. The gamma-counting rate of the blood plasma was recorded at 13 intervals during the 96 hours subsequent to the bleedings. Gamma curves, uncorrected for nuclear decay, were biphasic for 151 of the 194 samples. Recognizable first components (mean half-life [plus or minus] s.e.m., 6.12 [plus or minus] 0.10 hours) represented the buildup of 99Tcm to equilibrium levels in 53 samples (38 of these from rabbits fed on control diets) and decay of "excess" 99Tcm in 101 others (65 for rabbits fed on diets containing 0. 4% Na2MoO4). The second components (mean half-life 65.9 [plus or minus] 1.1 hours) represented a condition of transient equilibrium between 99Mo present in the samples at time of bleeding and the daughter nuclide. Biological differentiation of 99Mo and 99Tcm as observed in this study indicated that the indiscriminate measurement of gamma emissions for 99Mo-containing systems may give apparent 99mo concentrations 0. 57-2. 31 times the actual values. Counting of either the total beta emission or a specific 99Mo gamma energy is recommended when the measurement of 99M0 is attempted.

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