TC-99m Physical Decay Calculator
Use this tool to estimate remaining technetium-99m activity after a given elapsed time, using the standard exponential decay model.
What is Tc-99m and why decay matters
Technetium-99m (Tc-99m) is one of the most common radionuclides used in diagnostic nuclear medicine. Because its physical half-life is about 6 hours, activity drops meaningfully throughout the day. Knowing the current activity is essential for practical decisions such as dose preparation, schedule timing, and quality checks.
The decay equation used in this calculator
This calculator applies pure physical decay:
- A(t) = remaining activity at time t
- A0 = initial activity
- T½ = half-life
- t = elapsed time
For Tc-99m, a common half-life value is approximately 6.01 hours. Some systems use slightly different constants based on calibration conventions; always follow your institutional standard when needed.
How to use this decay calculator tc99m
Step-by-step
- Enter the initial activity and choose mCi or MBq.
- Enter the elapsed time and time unit.
- Confirm half-life (default 6.01 hours for Tc-99m).
- Optionally enter a target activity to estimate when that level will be reached.
- Click Calculate Decay to view remaining activity and related values.
What results include
- Remaining activity
- Total activity decayed
- Percent remaining and percent decayed
- Elapsed half-lives
- Decay constant and mean life
- Time to target activity (optional)
Quick Tc-99m reference table
Approximate fraction remaining for a 6.01-hour half-life:
| Elapsed Time | Fraction Remaining | Percent Remaining |
|---|---|---|
| 0 hours | 1.000 | 100% |
| 3 hours | ~0.707 | ~70.7% |
| 6 hours | ~0.500 | ~50.0% |
| 9 hours | ~0.354 | ~35.4% |
| 12 hours | ~0.250 | ~25.0% |
| 18 hours | ~0.125 | ~12.5% |
| 24 hours | ~0.062 | ~6.2% |
mCi and MBq conversion
The calculator keeps your selected input unit and also shows the alternate unit in the result output.
- 1 mCi = 37 MBq
- 1 MBq = 0.0270 mCi (approx.)
Important usage notes
Physical decay vs biological clearance
This tool models physical decay only. In real patients, effective activity can also change due to biological distribution and clearance. For clinical decision-making, use official protocols and site procedures.
Rounding and calibration
Small differences can occur depending on rounding, instrument calibration, and exact half-life values configured in local systems.
Bottom line
If you need a fast and reliable decay calculator tc99m, this page gives a practical estimate for routine planning and checks. It is intended for educational and operational support and should not replace local policy, medical direction, or regulatory guidance.