If a Mo99/Tc-99m generator is eluted at 0700 and 1300, what will happen to the Tc-99m yield at 0700 the next day?

When considering the yield of Tc-99m from a Mo-99/Tc-99m generator, it is important to understand the decay characteristics of Mo-99 and how it replenishes Tc-99m.

Mo-99 has a half-life of approximately 66 hours, meaning that over time, the amount of Mo-99 in the generator will decrease significantly due to radioactive decay. When elution occurs at 0700 and again at 1300, it extracts the available Tc-99m, which is produced from the decay of Mo-99. Between the two elution times, there will still be some production of Tc-99m from the remaining Mo-99.

However, by 0700 on the next day, the remaining Mo-99 quantity is expected to be at a lower level due to its radioactive decay; therefore, the amount of Tc-99m available for elution will also be decreased. As a result, the yield of Tc-99m at 0700 the next day will be lower than it was on the previous day.

This decline in yield explains why the correct choice is associated with a decrease in the amount of Tc-99m produced.