Question

Calculate the exact time at which the first three 'milkings' of the technetium cow should be performed.

Answer 1

Radionuclide generators are devices that produce a useful short-lived medical radionuclide (known as “daughter”) from the radioactive transformation of a non-medical long-lived radionuclide (called a “parent”).

Technetium Cow- A technetium-99m generator, is a device used to extract the metastable isotope 99mTc from a source of decaying molydenum-99.

Milking - For generator systems to be practical, the parent must have a relatively long half-life compared to that of the daughter, and the generator device (often referred as a "cow") must provide for repeated separations of the daughter product. This separation process is called an elution (colloquially it is also referred to as a "milking").

• As the parent, Mo-99, decays, the concentration of the daughter, Tc-99m, increases in the column. Tc-99m reaches a maximum after about 24 hours
• When the ratio of the rate of production of the daughter and rate of decay of the daughter stabilize, the system is said to be in equilibrium.
• in the Mo-99-Tc-99m radionuclide generator, the half-life of the parent nuclide is much longer than that of the daughter nuclide. About 50% of the equilibrium activity is reached within one daughter half-life, 75% within two daughter half-lives and so on.
• It takes about 4 daughter half-lives to reach equilibrium with the parent.

99Mo has a half-life of 66 hours.

Half Life of Tc-99m is 6 hours.

Four half lives = 24 hours.

The first milking process occurs after 24 hours.

Removing the daughter nuclide from the generator is reasonably done every 6 hours or, at most, twice daily in a Mo-99-Tc-99m generator.

2nd milking process after 24 + 6 = 30 hours..

3rd milking process after 30 + 6 = 36 hours.