The Molybdenum-Technetium Generator
- A molybdenum–technetium generator is a device that produces technetium from molybdenum
- Technetium-99m (Tc-99) has a half-life of 6.0 hours
- This allows it to be used as a tracer with low irradiation of the patient, thanks to the short half-life
- The short half-life, however, means it must be produced in the hospital when needed, as it cannot maintain the required levels of radioactivity for long periods of time
- Molybdenum-99 (Mo-99) has a half-life of 66 hours (2.8 days)
- It is produced in nuclear reactors, and due to its slightly longer half-life, it can be transported to hospitals every week
- Once Mo-99 arrives at a hospital, it can be placed in a molybdenum-technetium generator to produce Tc-99m
- In the generator, Mo-99 decays over the course of a few days, producing Tc-99m for up to a week
- Tc-99m is extracted from the generator every few days by passing a saline solution over the radioactive materials
- Tc-99m enters the solution, which can then be extracted and injected into patients ready for scanning
Worked example
A medic suggests that the molybdenum-technetium generator should be kept at the nuclear power station and Tc-99m should just be shipped into the hospital.
It is a 12 hour journey for a truck from the nearest nuclear power station.
Calculate the percentage of Tc-99m lost in the process of supplying the hospital with 1 kg of Tc-99m.
The half-life of Tc-99m is 6.0 hours.
Answer:
Step 1: Determine the number of half-lives that pass during the journey
- The journey is 12 hours long
- Two half-lives pass over the course of the journey
Step 2: Determine the initial mass of Tc-99m
- Mass has halved twice to reach 1 kg
- Initial mass was 4 kg
Step 3: Determine the percentage of Tc-99m lost
- 3 kg of Tc-99m was lost
- This is 75% of the initial mass
Exam Tip
You don't need to know the ins-and-outs of the molybdenum-technetium generator, but expect to come across questions regarding the half-lives of each radioisotope and why the generator is required.
