Radiation safety math
Understand gamma-source units, dose rate, distance, shielding and decay through worked examples. These are educational estimates, not operational safety decisions.
Start with units, then dose rate, distance, shielding and stay time. Finish with decay and the sources inside portable gauges. Each guide shows the arithmetic, assumptions and published sources.
Use these pages to understand a calculation. For field decisions, use a calibrated survey instrument, your radiation safety officer and the conditions of your license.
7 articles by Steven Michael Barber.
Radiation units explained: Sv vs rem, Gy vs rad, Bq vs Ci
Practical guide
What activity, absorbed dose and equivalent dose each measure, the exact SI and traditional unit conversions, and where the roentgen and weighting factors fit.
Gamma dose rate, distance and shielding
Practical guide
How the point-source formula, the inverse-square law and half-value layers of lead, steel and concrete set the dose rate from a gamma source, worked out.
Distance is the cheapest shield: the inverse-square law in practice
Practical guide
Use inverse-square estimates to compare distance and shielding, understand model limits and distinguish calculated contours from surveyed boundaries.
Half-value layers compared: lead, steel and concrete for Cs-137, Co-60 and Ir-192
Practical guide
Half-value and tenth-value layers of lead, steel and concrete for the common industrial gamma sources, by thickness and by weight, with a worked shield.
Stay time and dose budgets: working from dose rate and time
Practical guide
Work through illustrative dose budgets and rate-times-time examples, with federal limits and the measurements and procedures that govern real work.
Radioactive decay and half-life
Practical guide
The decay law in plain terms: how to work out the activity left after a given time, how long a source takes to fall to a given level, and the mistakes to avoid.
Portable nuclear gauges explained: the sources inside, the leak test and the license
Practical guide
What is inside a moisture-density gauge, how it measures, how its cesium and americium sources age, and the dated duties of the license and every trip to a job.