Plan radiation work by estimating needed separation quickly. Supports reference measurements and source constants too. Export results for reports, checks, and safer decisions today.
This calculator uses the inverse-square relationship for point-source radiation fields. If you have a reference measurement:
D₂ = D₁ × (r₁ / r₂)² so
r₂ = r₁ × √(D₁ / D₂)
If you have a radionuclide gamma constant Γ and activity A:
D = ΓA / r² so
r = √(ΓA / D)
| Scenario | Method | Inputs | Target dose rate | Estimated distance |
|---|---|---|---|---|
| Survey meter planning | Reference | 1200 µSv/h at 1 m | 10 µSv/h | ≈ 10.95 m |
| Controlled boundary | Reference | 2 mSv/h at 0.5 m | 50 µSv/h | ≈ 3.16 m |
| Source estimate | Source + Γ | A = 37 MBq, Γ = 0.084 (mSv·m²)/(h·GBq) | 5 µSv/h | ≈ 2.49 m |
| Conservative spacing | Reference | 800 µSv/h at 1 m, safety factor 2 | 20 µSv/h | ≈ 8.94 m |
| Quick check | Reference | 300 µSv/h at 2 m | 30 µSv/h | ≈ 6.32 m |
This tool estimates how far you should be from a radiation source to achieve a chosen dose rate at that location. It is designed for planning boundaries, walk‑downs, and controlled-area layouts when you need a fast, unit-consistent distance estimate and a simple record for documentation.
If you have a survey reading at a known distance, the calculator scales that measurement using inverse-square behavior. Because the reading already reflects your setup, it can capture effects such as partial shielding and local scatter better than a purely theoretical model. Example: 1200 µSv/h at 1 m scales to about 10.95 m for 10 µSv/h.
When measurements are not available, you can estimate dose rate from activity A and gamma constant Γ using D = ΓA / r². After converting units to Bq and (Sv·m²)/(h·Bq), the calculator solves r = √(ΓA / D). This is useful for early-stage planning, shipping checks, and quick screening calculations.
Dose rate values are normalized internally to Sv/h, while activity converts to Bq from common metric and curie-based units. Distance is computed in meters, then also shown in centimeters and feet to match typical field notes and signage needs.
A safety factor reduces the effective target dose rate, increasing the recommended distance. A factor of 2 plans for half the entered target dose rate. Use this margin when uncertainty is high, occupancy varies, or ALARA practice requires extra conservatism. For public areas, combine the factor with postings and re-surveys during the job to confirm stability.
Inverse-square scaling assumes a point source and relatively open geometry. Extended sources, collimated beams, nearby walls, or heavy shielding can shift the falloff. If readings are inconsistent with distance, rely on representative reference measurements and re-calculate after configuration changes.
Choose a target dose rate that matches your procedure, select a method, and enter inputs with correct units. Add notes describing shielding, source state, and measurement position. After calculating, export CSV or PDF to attach to work packages, briefings, or shift logs.
The distance is a planning estimate, not a guarantee. Always verify with calibrated instruments, consider time and occupancy, and update the calculation if source strength, geometry, or shielding changes. Prefer the reference method when real measurements are available.
Use the reference measurement method when you have a reliable survey reading at a known distance. Use the source + Γ method when you only know activity and a suitable gamma constant for your radionuclide.
The safety factor makes the calculator more conservative by lowering the effective target dose rate. A higher factor increases the computed distance to provide extra margin against uncertainty and changing conditions.
Shielding is included only if your reference dose rate was measured with that shielding in place. The source + Γ method is an unshielded point-source style estimate unless your Γ value already accounts for attenuation.
Scatter from walls, floor, equipment, and air, plus extended source size or collimation, can change how dose rate falls with distance. Use representative measurements and re-check after moving the source or adding shielding.
It can support planning when you have a reference measurement at a known distance. For machine sources with beam direction, filtration, or duty cycle, the inverse-square assumption may not hold everywhere, so verify with surveys.
Choose the unit that matches your instruments or paperwork. The calculator converts internally to Sv/h, so results are consistent. Ensure you enter the numeric value and unit that belong together.
The PDF is a concise calculation record with inputs and outputs. For audits, attach supporting data such as instrument ID, calibration status, measurement geometry, shielding description, and the applicable site dose-rate limits.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.