Why technetium-99m for biomedical radiodiagnostic is not a carrier-free radionuclide? Analytical behavior of its 'isotopic dilution factor' with time

Technetium-99m is used extensively in radiodiagnostics and it is usually called a carrier-free radionuclide. This statement is substantially wrong for several reasons: firstly, 99mTc obtained by its parent 'generator' 99Mo decays by IT - before and after elution - on its long-lived ground level 99gTc, which constitutes an unavoidable isotopic carrier. The behavior vs. time of isotopic dilution factor of no carrier added 99mTc is calculated analytically. In case of production of 99mTc via 98 Mo(n,g)99Mo/99mTc route, no other radioisotopic impurities other than 99gTc are expected, whereas if 99Mo is produced by fission of enriched 125U (fission-moly), 97gTc, 98Tc and 99gTc are produced as direct fission by-products. The yields of direct fission production of 97gTc, 98Tc and 99gTc are calculated with the theory of fission as a function of Z. Because 100 % yield radiochemistry cannot exist, these Tc radionuclides are present in 99Mo, even after several elutions of 99mTc for radiopharmaceutical applications. Secondly, Tc is not an artificial element, because its long-lived radionuclides 98Tc, 99gTc and 97gTc are present in the environment as fission and activation products of U and Th ores. Finally, production by accelerator through light ion irradiation on Mo or other targets leads to a no carrier added 99mTc too