Radiation Dose Exposure Calculator
Calculates the radiation dose received from a point gamma source from its dose rate at 1 m, exposure time, distance and shielding. Used in radiation safety planning, occupational health, and emergency response.
Last updated: September 2026
Formula below · 2 sources (nrc.gov, Wikipedia) · Updated Sep 2026
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About this calculator
For a point source the dose rate falls with the square of distance, so the dose received is: Dose (mSv) = dose rate at 1 m (mSv/h) × exposure time (h) / distance² (m²) × shielding transmission. The shielding options give the fraction of dose that passes through each barrier for cobalt-60-energy gamma rays, from broad-beam tenth-value layers (NCRP Report 49: lead 4.0 cm, steel 6.9 cm, concrete 20.6 cm per factor of ten), so they already include scattered radiation; for lower-energy sources such as Cs-137 the real transmission is smaller, so these values err on the safe side. Dose is not scaled by body weight: sieverts already express energy per kilogram of tissue. Annual occupational dose limits set by the ICRP are 20 mSv per year averaged over five years; the public limit is 1 mSv per year.
How to use
Suppose a source gives 10 mSv/h at 1 m, and a worker spends 0.5 hours at 2 m behind a 2 cm steel plate. Step 1: dose rate × time = 10 × 0.5 = 5 mSv at 1 m. Step 2: inverse square at 2 m: 5 / 2² = 1.25 mSv. Step 3: steel 2 cm transmits about 51%: 1.25 × 0.51 = 0.64 mSv. Behind 5 cm of lead instead it would be 1.25 × 0.06 = 0.075 mSv.
Frequently asked questions
What is a safe level of radiation dose exposure for humans?
Background radiation from natural sources exposes the average person to about 2–3 mSv per year globally, varying significantly by location. Occupational dose limits set by the International Commission on Radiological Protection (ICRP) are 20 mSv per year averaged over five years, with a single-year maximum of 50 mSv. Medical procedures such as CT scans may deliver 2–20 mSv per examination. Acute doses above 1,000 mSv (1 Sv) can cause radiation sickness, while doses above 4–5 Sv are potentially lethal without medical treatment.
How does distance from a radiation source reduce your effective dose?
Radiation from a point source spreads outward in all directions, covering an ever-larger spherical surface as distance increases. Because the same total energy is spread over a surface area proportional to the square of the radius, the intensity — and thus dose rate — falls as 1/distance². This is the inverse-square law. Doubling your distance from the source reduces your dose to one-quarter. This principle is one of the three fundamental radiation protection strategies: time, distance, and shielding.
What types of shielding materials are most effective against different radiation types?
Alpha particles are stopped by a sheet of paper or a few centimeters of air, making external shielding trivial but inhalation hazardous. Beta particles are effectively blocked by a few millimeters of plastic, glass, or aluminum. Gamma rays and X-rays, being highly penetrating electromagnetic radiation, require dense materials such as lead, concrete, or thick steel to attenuate significantly. Neutrons, produced in nuclear reactors and some isotope sources, are best moderated and absorbed by hydrogen-rich materials like water or polyethylene, often combined with boron or cadmium.