Calculator
Fixed-site zoning
Distances at which the dose rate falls below each threshold, for a gamma source on a fixed site. The collimator lowers the on-axis dose rate by the isotope factor.
| Zone | Limite | Distance |
|---|---|---|
| Supervised area (low threshold) | — | — — |
| Controlled area — green | — | — — |
| Controlled area — yellow | — | — — |
| Controlled area — orange | — | — — |
| Exclusion area | — | — — |
- Dose constant K
- —
- Collimator
- —
Distances rounded to the nearest decimetre; the feet value is indicative.
Method
K = A × 0.037 × Γ
r = √(K / Ḣ)
- A — activity in Ci
- Γ — isotope gamma constant in mSv·m²/(h·TBq)
- K — dose constant in mSv·m²/h
- Ḣ — dose rate threshold in mSv/h (µSv/h ÷ 1000)
- r — distance in m
With a collimator, K is divided by the isotope factor (250 for Ir-192 and Se-75, 10 for Co-60). The calculation assumes a point source, no shielding, no scatter and no air attenuation: it is an upper bound.
The ASN thresholds are a French reference. If your Luxembourg authorisation sets different values, use custom mode. 0.5 µSv/h is a low working value, not a legal limit.
Indicative result — check it against your authorisation and your dosimetry.