Nuclear Radiation Shielding Calculator
Calculates the required shielding thickness to reduce gamma radiation from a radioactive source to a safe dose rate at a given working distance. Use it when designing barriers around radiation sources in medical, industrial, or nuclear facilities.
Last updated: September 2026
Formula below · 2 sources (nrc.gov, Wikipedia) · Updated Sep 2026
Compare with similar
About this calculator
The unshielded dose rate from a point gamma source at distance d is Γ × A / d², where Γ is the isotope's gamma-ray constant (R·m²/Ci·h: Co-60 1.32, Cs-137 0.33, Ir-192 0.59 taken at the conservative end) and 1 R ≈ 10 mSv. The shield must reduce that by the factor F = unshielded / target dose rate. With broad-beam tenth-value layers (TVLs), which include scattered-photon buildup, the thickness is TVL × log₁₀(F). TVLs (NCRP Report 49): Co-60 — lead 4.0 cm, steel 6.9 cm, concrete 20.6 cm; Cs-137 — lead 2.1, steel 5.3, concrete 15.7 cm. Water is scaled from concrete by density (48 and 37 cm) and tungsten from lead by density with a margin (2.6 and 1.4 cm). Ir-192 uses the Cs-137 TVLs, which are thicker than its own, so the estimate errs on the safe side. Results assume a point source, a single primary barrier and no gaps; a qualified expert must confirm any real design and survey it after installation.
How to use
Example: 10 Ci of Co-60, a target of 0.025 mSv/h at a working distance of 60 cm, lead shield. Step 1: unshielded dose rate = 1.32 × 10 × 10 / 0.6² = 366.7 mSv/h. Step 2: reduction F = 366.7 / 0.025 = 14,667, log₁₀ F = 4.17 TVLs. Step 3: thickness = 4.17 × 4.0 = 16.7 cm of lead (85.8 cm of concrete). For the same Cs-137 activity the unshielded rate is 4× lower and lead's TVL is 2.1 cm: 3.56 × 2.1 = 7.5 cm. The defaults (1,000 Ci Co-60 at 1 m, 0.025 mSv/h, concrete) need 117.9 cm.
Frequently asked questions
What is a half-value layer and how does it determine shielding thickness?
A half-value layer (HVL) is the thickness of a specific material needed to reduce the intensity of gamma radiation by exactly 50%. Every additional HVL added halves the remaining dose rate again, giving exponential attenuation. For example, two HVLs reduce dose to 25%, three HVLs to 12.5%, and so on. The HVL depends on both the photon energy and the shielding material — lead has a much smaller HVL than concrete because of its much greater density and atomic number. To find the required thickness, you calculate how many HVLs are needed to bring the dose rate from the unshielded level down to the target limit, then multiply by the HVL of your chosen material.
Why does photon energy affect the required shielding thickness for gamma radiation?
Higher-energy gamma photons are more penetrating because they interact less often per centimetre. Below about 0.5 MeV the photoelectric effect dominates and high-Z materials such as lead are extremely effective; from about 0.5 to 5 MeV Compton scattering dominates and attenuation depends mainly on density. That is why lead's tenth-value layer roughly doubles from Cs-137 (0.662 MeV, 2.1 cm) to Co-60 (1.25 MeV, 4.0 cm). The source-isotope setting picks the matching gamma constant and TVLs.
How do tungsten, lead, steel, concrete, and water compare as gamma radiation shielding materials?
Per centimetre, tungsten (19.3 g/cm³) is the most effective, then lead (11.35), steel (7.9), concrete (2.35) and water (1.0); for the Compton-dominated energies of Co-60 and Cs-137, attenuation scales roughly with density. Broad-beam tenth-value layers for Co-60 are about 2.6 cm tungsten (estimated), 4.0 cm lead, 6.9 cm steel, 20.6 cm concrete and 48 cm water. Lead is the usual compact choice, concrete the economical structural choice for large walls, and water is used in pools where transparency and cooling matter.