What the half-life of Mo-99?

Technetium-99m's short half-life of6 hours makes storage impossible and would make transport very expensive. Instead its parent nuclide 99Mo is supplied to hospitals after its extraction from the neutron-irradiated uranium targets and its purification in dedicated processing facilities. It is shipped by specialised radiopharmaceutical companies in the form of technetium-99m generators worldwide or directly distributed to the local market. The generators, colloquially known as a moly cows, are devices designed to provide radiation shielding for transport and to minimize the extraction work done at the medical facility. A typical dose rate at1 metre from Tc-99m generator is20-50 μSv/h during transport. These generators' output declines with time and must be replaced weekly, since the half-life of 99Mo is still only66 hours.

Since the half-life of the parent nuclide (99Mo) is much longer than that of the daughter nuclide (99mTc),50% of equilibrium activity is reached within one daughter half-life,75% within two daughter half-lives. Hence, removing the daughter nuclide (elution process) from the generator ("milking" the cow) is reasonably done as often as every6 hours in a 99Mo/99mTc generator.

Molybdenum-99 (66 h)*: Used as the 'parent' in a generator to produce technetium-99m.

Technetium-99m (6 h): Used in to image the skeleton and heart muscle in particular, but also for brain, thyroid, lungs (perfusion and ventilation), liver, spleen, kidney (structure and filtration rate), gall bladder, bone marrow, salivary and lacrimal glands, heart blood pool, infection and numerous specialised medical studies.  Produced from Mo-99 in a generator.

Molybdenum-99 (Mo-99) has a life time of about66 hours; before decaying to Technetium-99m (Tc-99m) which has a life time of only6 hours.

(Tc-99m) is probably the most widely used isotope in Nuclear Medicine.