Radiation protection
Inverse Square & Shielding Estimator
Calculate how dose rate changes with distance and shielding to support ALARA planning, room design, and exposure monitoring. Units can be any consistent combination (e.g., mSv/h, feet or meters, minutes).
Dose rate measured at the reference distance.
Remaining fraction after shielding (e.g., 0.25 for 75% attenuation).
Optional: calculate cumulative dose over this time.
Optional: compute time to reach occupational or public dose limits.
Adjusted dose rate
0.031 mSv/h
Inverse square × shielding applied.
Cumulative dose
0.008 mSv
Over 15 minutes.
Time to dose limit
1920.0 minutes
Manageable dose rateMonitor accumulated dose and ensure ALARA practices are in place.
How to Use This Calculator
Measure or obtain reference dose rate
Use survey instruments or manufacturer data at a known distance from the source.
Determine shielding transmission
Consult tenth-value layer tables or measured attenuation for lead, concrete, or mobile barriers.
Plan exposure time accordingly
Compare cumulative dose with occupational or public dose limits and adjust workflows as necessary.
Formula
Inverse square law: D₂ = D₁ × (d₁ ÷ d₂)²
Shielding: Dshielded = D₂ × Transmission fraction
Cumulative dose = Dose rate × Time
Time to limit = Dose limit ÷ Dose rate
Full Description
Radiation intensity diminishes with the square of distance from a point source—a key principle in shielding design. Additional protection comes from materials that attenuate the beam. Combining distance, time, and shielding (the “three pillars” of radiation protection) supports As Low As Reasonably Achievable (ALARA) practice in medical, industrial, and research settings.
Use this calculator to model new barrier thickness, evaluate staff workflows, or communicate safety strategies. Remember that scatter fields, patient attenuation, and non-isotropic sources may require more sophisticated modeling or Monte Carlo analysis.
Frequently Asked Questions
How do I estimate shielding transmission?
Use TVL (tenth-value layer) or HVL (half-value layer) data for the energy spectrum. Transmission = 10-n where n = thickness ÷ TVL.
Does this apply to extended sources?
The inverse square law assumes a point source. For extended sources or scatter fields, use measured data or specialized dose modeling.
Can I convert between mSv and mrem?
Yes. 1 mSv = 100 mrem. Multiply dose and dose rates accordingly if using customary units.
What if shielding also reduces scatter directionally?
Transmission factors may vary by angle. Use measured attenuation for the specific geometry when available.