03 Nuclear
Mo-99 / Tc-99m generator
Daughter activity in transient equilibrium after ingrowth time.
Listen
Listen · English
Simulation
Mo-99 / Tc-99m generator — Change the numbers; the scene follows.
Where it works
Hot lab
Generator
At the Mo-99/Tc-99m generator — elution yield, secular equilibrium, Mo breakthrough.
Open this machineFormula
Variables
Results
A_Tc
Technetium activity
13.5157GBq
A_Tc/A_Mo(0)
Ratio
0.6758
Curve
Explanation
What it means
A Mo-99/Tc-99m generator is a classic transient-equilibrium parent–daughter pair. Tc-99m grows in with T½ = 6.02 h while Mo-99 (66 h) slowly decays; activity peaks around 24 h after a perfect elution. Branching to Tc-99m is ~86%. This is a working relation in Nuclear medicine.
Where it is used
Clinically it sits on the Hot lab — Generator. At the Mo-99/Tc-99m generator — elution yield, secular equilibrium, Mo breakthrough. Nuclear-medicine relations sit in the hot lab, on the camera, and in the voxel: decay, SUV, TOF, and counting statistics. They decide whether an uptake is real or a clock error.
Hot lab · Open this machineHow to use it
Enter Mo activity at t = 0 (post-elution). The curve over 72 h shows ingrowth. Real generators never reach the theoretical maximum because of incomplete elution and Tc-99 (ground state) buildup. Change one input and watch the curve and the simulation follow.
Symbols
- A_MoMolybdenum activity20 GBq
- T½_MoMo half-life66 h
- T½_TcTc half-life6.02 h
- fBranching fraction0.86
- tIngrowth time24 h
Worked example
A typical case from the default values: A_Mo = 20 GBq (Molybdenum activity); T½_Mo = 66 h (Mo half-life); T½_Tc = 6.02 h (Tc half-life); f = 0.86 (Branching fraction); t = 24 h (Ingrowth time). Substituting into the relation gives A_Tc = 13.5157 GBq; A_Tc/A_Mo(0) = 0.6758. These are teaching numbers — align them with your machine.
Typical values give
- A_Tc = 13.5157GBq
- A_Tc/A_Mo(0) = 0.6758
Where it comes from
The displayed formula is the working relation. Daughter activity in transient equilibrium after ingrowth time. Usual reference: Cherry, generators. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Cherry, generators
Assumptions & limits
Bateman equation with two species and a constant branching fraction. No Mo breakthrough, no Tc-99m remaining after elution (assumes perfect milk-out at t=0).
Pitfalls
Activity is not counts. SUV needs the true injected activity, the residual, and the correct decay time — a clock off by 10 min on ¹⁸F is a several-percent error. Do not compare SUVs across reconstructions. Bateman equation with two species and a constant branching fraction. No Mo breakthrough, no Tc-99m remaining after elution (assumes perfect milk-out at t=0).
Keep this
f ≈ 0.86 branching to Tc-99m. T½(Mo)=66 h, T½(Tc)=6.02 h.
In this specialty