Calibration of the massic activity of a solution of 99Tc

A solution of 99Tc was calibrated in terms of massic activity using the NIST 4πβ(LS)–γ-anticoincidence counting system. 60Co was used as the efficiency-tracing radionuclide. Measurements were also made using conventional 4πβ liquid-scintillation (LS) counting. 3H was used as the efficiency-monitor radionuclide. The LS detection efficiency ratios, (ε99/ε3), were calculated theoretically. The calculated detection efficiency ratios depend strongly upon the assumed shape of the beta spectrum of 99Tc.