EngineerHub.orgScreen natural radioactivity in building materials
Enter measured Ra-226, Th-232 and K-40 activity concentrations. The calculator evaluates gamma dose rate and commonly used screening indices.
Material inputs
Screening results
Background
Open a section to understand the model, equations and limitations.
I = CRa/300 + CTh/200 + CK/3000
This is a conservative screening index used in European and IAEA guidance contexts. It is not a universal compliance certificate.
D = 0.462 CRa + 0.604 CTh + 0.0417 CK
The result is absorbed dose rate in air in nGy/h for a broad environmental geometry. A building-specific model can differ.
Radium equivalent activity and external/internal hazard indices are widely reported in material studies. They are convenient comparisons but should not be mistaken for direct measurements of personal dose.
A complete evaluation considers representative sampling, density, thickness, room geometry, material fraction, occupancy, secular equilibrium, radon exhalation and national regulatory criteria.
For a material containing 40 Bq/kg Ra-226, 30 Bq/kg Th-232 and 400 Bq/kg K-40:
D = 0.462(40) + 0.604(30) + 0.0417(400) = 53.3 nGy/h
Using the calculator defaults of 0.7 Sv/Gy and 7000 indoor hours/year:
E = 53.3 × 7000 × 0.7 ÷ 10⁶ = 0.261 mSv/year
The activity concentration index is 0.417. This example demonstrates the page calculation but does not represent a universal compliance decision because real room geometry, material use, wall thickness and national rules matter.
IAEA safety standards use a reference level of approximately 1 mSv/year for indoor external gamma exposure from radionuclides in building materials. The activity concentration index is a conservative screening tool for identifying materials that may need further assessment; it is not a stand-alone legal pass/fail test.
Some countries adopt lower values or additional controls. Always compare with the applicable national regulation and the intended use of the material.
Frequently Asked Questions
Practical questions about interpretation and use.
Not universally. It is a screening index. National rules, intended use, material geometry and the applicable dose reference level determine compliance.
They represent the main natural gamma-emitting series and potassium contribution commonly measured in construction materials.
No. Radon exhalation depends on radium availability, emanation, diffusion, surface area and ventilation. Gamma indices cannot substitute for a radon assessment.
Only when the relevant decay-chain equilibrium and analytical basis are understood. The calculator labels the input as Ra-226 because disequilibrium can occur in processed materials.