Radiation Exposure Rate Calculator
Understanding Radiation Exposure Rate
In the fields of health physics, industrial radiography, and nuclear safety, calculating the Exposure Rate is a fundamental task for ensuring personnel safety. The exposure rate determines the intensity of radiation at a specific distance from a radioactive source.
This calculator uses the standard "Inverse Square Law" combined with the specific Gamma constant of the radioactive isotope to determine how many Roentgens per hour (R/h) a person or object would be exposed to at a given distance.
The Exposure Rate Formula
For a point source of radiation, the exposure rate is calculated using the following formula:
Where:
- X = Exposure Rate (Roentgens per hour, R/h)
- Γ (Gamma) = Specific Gamma Ray Constant (R·m²/Ci·h)
- A = Activity of the source (Curies, Ci)
- d = Distance from the source (Meters)
Inverse Square Law Explained
The most critical component of this calculation is the distance (d). Because distance is squared in the denominator (d²), doubling your distance from a radiation source reduces the exposure rate by a factor of four. Conversely, halving your distance increases the exposure by a factor of four.
This principle is a cornerstone of the ALARA (As Low As Reasonably Achievable) safety concept: Time, Distance, and Shielding.
Common Gamma Constants
Different isotopes emit gamma rays at different energies and probabilities. The Gamma Constant (Γ) normalizes these factors for calculation. Here are common approximate values used in industrial radiography:
- Cobalt-60 (Co-60): 1.32 R·m²/Ci·h (High energy, used in sterilization and therapy)
- Cesium-137 (Cs-137): 0.33 R·m²/Ci·h (Used in calibration equipment)
- Iridium-192 (Ir-192): 0.48 R·m²/Ci·h (Standard for industrial radiography/NDT)
How to Use This Calculator
- Select Isotope: Choose a common isotope from the dropdown menu to auto-fill the Gamma Constant. If your isotope isn't listed, select "Custom" and enter the constant manually.
- Enter Activity: Input the current activity of the source in Curies (Ci). Note that activity decays over time, so ensure you use the current activity, not the initial activity at the time of manufacture.
- Enter Distance: Input the distance between the source and the point of measurement in meters.
- Calculate: Press the button to see the result in Roentgens per hour (R/h) and milliRoentgens per hour (mR/h).
Disclaimer: This calculator is for educational and estimation purposes only. It assumes a point source geometry and does not account for air attenuation or shielding. Always use calibrated survey meters for verifying actual radiation levels.