Calculator Inputs
The page stays in one main column, while the input fields use a responsive three, two, and one column grid.
Example Data Table
Example using initial activity 1200 Bq and half-life 5 days.
| Time (days) | Activity (Bq) | Remaining % |
|---|---|---|
| 0 | 1200 | 100% |
| 5 | 600 | 50% |
| 10 | 300 | 25% |
| 15 | 150 | 12.5% |
| 20 | 75 | 6.25% |
Formula Used
A(t) is the activity after elapsed time t. A₀ is the initial activity. λ is the decay constant. N(t) is the remaining number of undecayed nuclei.
When a target activity is known, the time to reach that target comes from rearranging the exponential law:
This calculator assumes a single radionuclide, constant decay constant, and no daughter product buildup.
How to Use This Calculator
- Enter a sample label to identify the run.
- Choose whether you want to define decay using half-life or decay constant.
- Enter initial activity, initial nuclei, or both.
- Set elapsed time and choose matching units.
- Optionally enter a target activity and a target remaining percent.
- Choose chart points for smoother or lighter graphs.
- Press the calculate button to show results above the form.
- Use the download buttons to export the current results as CSV or PDF.
FAQs
1. What does activity mean in this calculator?
Activity is the decay rate of a radioactive sample. It tells you how many nuclear disintegrations happen each second or other selected time unit.
2. When should I use half-life instead of decay constant?
Use half-life when the nuclide is described by the time required to drop to half its value. Use decay constant when the rate constant is already known.
3. Can I enter only nuclei without initial activity?
Yes. If you provide nuclei and a valid decay constant source, the calculator derives initial activity through A = λN automatically.
4. Why do activity and nuclei both decrease exponentially?
Each undecayed nucleus has the same constant probability of decaying. That statistical behavior produces the same exponential factor for both activity and remaining nuclei.
5. What is mean lifetime?
Mean lifetime is the average survival time of a nucleus before decay. It equals 1 divided by the decay constant and differs from half-life.
6. Does this model include daughter isotope buildup?
No. This page models one-step decay only. It does not include decay chains, branching ratios, shielding, or detector efficiency corrections.
7. Why might my initial activity and nuclei seem inconsistent?
If both are entered, they should satisfy A = λN. Small differences can come from rounding, unit conversion mistakes, or mixing measurements from different moments.
8. Can I use curies instead of becquerels?
Yes. The calculator supports Bq, kBq, MBq, GBq, Ci, mCi, microcurie, and nCi, then converts internally for consistent physics calculations.