EngineerHub.orgChoose the physical model that matches the radiation
Shielding is not one universal thickness equation. The dominant interaction mechanism changes with radiation type, energy, material composition, source geometry and the quantity being limited.
How to use this calculator
Follow the four steps below. The page changes its inputs and equations when you change radiation type.
Inputs
Quick examples
Results
Attenuation curve
Calculated transmission through the selected material.
Material comparison
Compare idealized thicknesses under the same input conditions.
Background
Open any section for the physical basis, assumptions and design limitations.
For an idealized monoenergetic narrow beam, the uncollided intensity follows I = I₀e−μx. The linear coefficient is μ = (μ/ρ)ρ, so both composition and density matter.
The photon presets interpolate NIST mass attenuation coefficients. Absorption edges and mixed spectra can make a single representative energy inadequate, particularly for diagnostic X-ray beams.
The half-value layer is HVL = ln(2)/μ; the tenth-value layer is TVL = ln(10)/μ. These are narrow-beam quantities.
Real shields receive scattered photons from the shield and surrounding structures. A buildup factor depends on energy, material, thickness and geometry; the constant allowance in this page is only a screening device.
The beta mode estimates the maximum practical range in areal density using the Katz–Penfold range–energy relation below 2.5 MeV and a linear extension above that range. Dividing by material density gives a physical thickness.
Low-Z plastics are normally placed closest to a beta source because dense high-Z materials increase bremsstrahlung production. High-energy or high-activity sources can require a second outer layer to attenuate the generated photons.
The fast-neutron screen uses R/R₀ = e−ΣRx. Removal coefficients are effective engineering parameters, not fundamental constants valid for every spectrum.
A practical neutron shield often combines hydrogen-rich material to slow neutrons, boron or another absorber to capture thermalized neutrons, and dense material to attenuate capture gamma radiation. Openings and streaming paths can dominate the result.
- Photons: compare attenuation, density, structural support, toxicity, fire performance, cost and buildability.
- Beta particles: use low-Z material close to the source and assess bremsstrahlung separately.
- Fast neutrons: use moderation plus capture and include secondary photon shielding.
- Alpha emitters: prioritize sealed containment, surface control, ventilation and prevention of intake.
Joints, penetrations, doors, cable routes, ducts, voids, density variation, moisture content, source distance, occupancy, skyshine and scattered fields can control a real design. Shielding blocks also impose structural, seismic and fire loads.
Photon mass attenuation presets are based on NIST X-Ray Mass Attenuation Coefficient tables. Beta guidance is checked against NIST ESTAR concepts and IAEA low-Z shielding guidance. Fast-neutron removal presets are legacy screening values from NBS Handbook 63.
NIST photon attenuation tables
NIST ESTAR electron range database
NBS Handbook 63 — neutron protection
Frequently Asked Questions
Practical questions about presets, equations and limitations.
No. Dense high-Z materials are useful for many photon fields, low-Z materials are normally preferred for beta shielding, and neutron shields typically require moderation, capture and secondary-photon control.
No. They represent idealized narrow-beam attenuation. Broad-beam geometry needs validated buildup treatment or transport analysis.
Photoelectric absorption, Compton scattering and pair production vary differently with photon energy and atomic number. The same material can therefore have very different HVL and TVL values at different energies.
They slow electrons with less bremsstrahlung production than lead or tungsten. An outer dense layer may still be needed when the generated bremsstrahlung is significant.
No. It is a removal-cross-section screen. Spectrum changes, capture reactions, secondary gamma production, geometry and penetrations require dedicated transport calculations.
It multiplies the idealized calculated thickness. It is not a substitute for uncertainty analysis, material tolerances, source uncertainty, construction quality or regulatory margins.
Only for education and preliminary comparisons. Final design requires a qualified specialist, validated source term, occupancy and distance assumptions, geometry, construction details and applicable regulation.