Point & Extended Sources
Point Source (Inverse Square Law)
Calculates exposure rate at a new distance or determines the required standoff distance to reach a target dose rate boundary from an isotropic point source.
I₁ × D₁² = I₂ × D₂²
Input Parameters
Calculation Goal
Target Boundary & Standoff Presets
Calculated Result & Visual Analysis
Nominal Solved Value Updated automatically
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Enter parameters on the left to calculate.
Geometry & Field Diagram
Interactive Model
Sensitivity Curve
Governing Equation & Parameters
Exposure₂ = Exposure₁ × (Distance₁ / Distance₂)²
| Symbol | Parameter | Default Unit | Definition |
|---|---|---|---|
| I₁ | R | Measured exposure or dose rate at the initial reference distance D₁. | |
| D₁ | cm | Distance from the source where I₁ was measured. | |
| I₂ | R | Resulting exposure or target boundary dose limit at distance D₂. | |
| D₂ | cm | New standoff distance from the point source. |
Health Physics Notes & Related Calculators
Operational Guidance
- Accurate when the measurement distance exceeds 3× the largest physical dimension of the source (d ≥ 3L).
- Doubling the distance from a point source reduces the dose rate to one-quarter (25%) of its initial value.
- Neglects air attenuation and scattering buildup, providing a conservative estimate for typical indoor survey distances under 10 meters.
Related Calculators
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