Inverse Square Law (Radiation)
Compute the radiation intensity at a new distance from a point source, I₂ = I₁·(d₁/d₂)², by the inverse square law: intensity falls with the square of distance. Doubling the distance reduces the dose to a quarter — which is why distance is one of the three basic radiation-protection defenses (time, distance and shielding) and the most effective and cheapest. Enter the initial intensity and distance and the new distance.
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Inverse square law (radiation)
A point source of radiation spreads its energy in every direction, over the surface of a sphere that grows with the square of the radius. The intensity reaching a given point therefore falls with the square of the distance: I₂ = I₁·(d₁/d₂)². The consequence for safety is powerful: doubling the distance cuts the dose to one quarter; tripling it, to one ninth. That is why distance is one of the three classic defences of radiation protection — alongside time (less exposure) and shielding — and the cheapest and most effective of the three: stepping a few metres away from a source, or handling it with long tongs and manipulators, drives the dose down sharply at no cost. (The law holds strictly for point sources in vacuum; extended sources or absorbing media bend the relation somewhat.) Enter the initial intensity and distance and the new distance.
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Radiation Shielding Attenuation
Compute the radiation intensity after passing through shielding, I = I₀·e^(−μ·x), by the exponential attenuation law, from the initial intensity (I₀), the material's linear attenuation coefficient (μ) and the thickness (x). Unlike alpha and beta particles (which have a finite range), gamma rays and X-rays are only exponentially attenuated — never fully blocked. It is the basis of shielding calculation. Enter the initial intensity, the attenuation coefficient and the thickness.
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Compute the exposure (or dose) rate of a point gamma source, X = Γ·A/d², from the exposure-rate constant (Γ, specific to the radionuclide), the source activity (A) and the distance (d). It combines the source strength with the inverse square law, allowing you to estimate the dose received at a given distance — fundamental in planning tasks with radioactive sources. Enter the gamma constant, the activity and the distance.
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