Radiation Dose Rate Calculator

Dose rate here is proportional to 1/d² (the inverse square law), not 1/d, because the same amount of radiation is spreading out over a spherical surface whose area grows with the square of distance. So doubling distance quadruples that surface area, spreading the same energy over four times the space and cutting dose rate to one-fourth — tripling distance cuts it to one-ninth, and so on.

It solves the dose rate equation backward: instead of computing dose rate at a given distance, it takes the public dose-rate target (derived from 1 mSv/year assuming 2,000 hours of annual exposure) and solves for the distance at which A×Γ/d² equals that target, which works out to d = √(A×Γ / target rate). The occupational limit distance uses the same approach with the higher 20 mSv/year target.

The gamma constant (Γ) is a fixed physical property of each radionuclide describing how much dose rate its gamma emissions produce at a given activity and distance — it depends on the isotope's specific gamma-ray energies and emission probabilities per decay. Co-60 emits two relatively high-energy gammas per decay, giving it a constant (0.351 mSv·m²/(GBq·hr)) roughly four times higher than Cs-137's (0.0842), meaning equal activities of Co-60 produce substantially more dose rate at the same distance.

No — it models an idealized bare point source in air with no intervening material, so it ignores any shielding, walls, or structures between you and the source, as well as buildup effects from scattered radiation and the finite size of real sources. If shielding is present, use the Radiation Shielding calculator to estimate its attenuation separately, since this dose-rate model will overstate actual exposure whenever real shielding exists.