Calculator Input
Example Data Table
This example uses 120 mSv/h at 1 meter.
| Distance (m) | Dose Rate (mSv/h) |
|---|---|
| 0.5 | 480 |
| 1 | 120 |
| 1.5 | 53.3333 |
| 2 | 30 |
| 3 | 13.3333 |
| 4 | 7.5 |
| 5 | 4.8 |
Formula Used
Inverse square law: D2 = D1 × (r1 / r2)2
Total dose: Total Dose = Target Dose Rate × Exposure Time
Required distance for a desired rate: rrequired = r1 × √(D1 / Ddesired)
D1 is the known dose rate. r1 is the known distance. D2 is the estimated dose rate at the new distance r2.
This relationship applies best to point sources with negligible attenuation between the source and the measurement point.
How to Use This Calculator
- Enter the known dose rate at a measured reference distance.
- Enter the target distance where dose is needed.
- Add exposure time to estimate accumulated dose.
- Optionally enter a desired dose rate target.
- Set graph limits to visualize distance response.
- Press calculate to display results above the form.
- Use CSV or PDF export for records.
- Review assumptions before using the estimate operationally.
Frequently Asked Questions
1. What does the inverse square law describe?
It describes how intensity changes with distance from a point source. When distance doubles, intensity becomes one fourth. When distance triples, intensity becomes one ninth.
2. Why does radiation dose drop so fast?
The same emitted energy spreads across a larger spherical area as distance increases. That spreading causes the measured dose rate to decrease with the square of distance.
3. When is this calculator most accurate?
It works best for point like sources, open geometry, and minimal attenuation. Accuracy falls when the source is extended, shielded, scattered, or surrounded by reflective structures.
4. Does this calculator include shielding effects?
No. It only models distance based change. Shielding, buildup, collimation, air attenuation, and detector efficiency should be handled separately for realistic field estimates.
5. Can I use different dose units?
Yes. The ratio calculation stays valid if units remain consistent. Keep the same dose rate unit everywhere, and pair exposure time with that unit correctly.
6. What is the difference between dose rate and total dose?
Dose rate is dose per unit time. Total dose is the accumulated exposure over a selected duration. This calculator reports both values separately.
7. What happens if I move closer than the reference distance?
The estimated dose rate increases sharply. Halving the distance multiplies dose rate by four, assuming the same geometry and no added shielding.
8. Can this be used for clinical or regulatory decisions?
Use it for education, planning, and quick screening. Final decisions should rely on qualified health physics review, calibrated measurements, and site specific procedures.