Calculator
Photon attenuation calculator
Half-value layer and transmission for gamma and X-ray beams through common materials.
At 662 keV, 5.54 mm of lead halves a narrow photon beam; 18.42 mm reduces it to one tenth. Choose a material, photon energy and thickness to calculate μ/ρ, μ, half-value layer (HVL), tenth-value layer (TVL), transmission and interaction-process shares.
Photon attenuation calculator: half-value layer and transmission
How much of a material stops how much of a gamma or X-ray beam. Mass attenuation coefficient by process, half- and tenth-value layers, mean free path and narrow-beam transmission, from NIST XCOM.
The calculator needs JavaScript. The reference values below are computed by the same code.
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Shielding reference: 15 common isotopes
HVL and TVL in mm for the selected gamma line. HVL halves the unscattered beam; TVL transmits 10%. These are single-energy, narrow-beam values without scattered-photon build-up, not full-spectrum dose shielding thicknesses.
| Isotope | Energy (keV) | Lead HVL / TVL (mm) | Concrete HVL / TVL (mm) | Steel (Fe) HVL / TVL (mm) | Water HVL / TVL (mm) |
|---|---|---|---|---|---|
| Cs-137 (via Ba-137m) | 661.657 | 5.54 / 18.4 | 38.7 / 129 | 12 / 39.8 | 80.8 / 268 |
| Co-60 | 1173.23 | 9.87 / 32.8 | 50.9 / 169 | 15.9 / 52.9 | 106 / 353 |
| Co-60 | 1332.49 | 10.9 / 36.2 | 54.3 / 180 | 17 / 56.5 | 113 / 376 |
| Ir-192 | 316.506 | 1.69 / 5.61 | 28.4 / 94.2 | 8.26 / 27.4 | 59.6 / 198 |
| Tc-99m | 140.511 | 0.258 / 0.856 | 20.5 / 68.1 | 4.12 / 13.7 | 45.1 / 150 |
| I-131 | 364.489 | 2.22 / 7.38 | 30 / 99.7 | 8.92 / 29.6 | 63 / 209 |
| F-18 (annihilation) | 511 | 3.91 / 13 | 34.5 / 115 | 10.6 / 35.1 | 72.2 / 240 |
| Am-241 | 59.5409 | 0.119 / 0.396 | 10.7 / 35.5 | 0.716 / 2.38 | 33.5 / 111 |
| Ra-226 (parent only) | 186.211 | 0.515 / 1.71 | 23.1 / 76.6 | 5.65 / 18.8 | 49.4 / 164 |
| Se-75 | 264.658 | 1.16 / 3.85 | 26.4 / 87.8 | 7.42 / 24.6 | 55.8 / 185 |
| Yb-169 | 63.12 | 0.139 / 0.46 | 11.5 / 38.2 | 0.832 / 2.77 | 34.4 / 114 |
| Lu-177 | 208.366 | 0.674 / 2.24 | 24.1 / 80 | 6.24 / 20.7 | 51.3 / 170 |
| Ga-68 (annihilation) | 511 | 3.91 / 13 | 34.5 / 115 | 10.6 / 35.1 | 72.2 / 240 |
| In-111 | 245.35 | 0.981 / 3.26 | 25.7 / 85.3 | 7.05 / 23.4 | 54.3 / 180 |
| Tl-201 | 167.43 | 0.398 / 1.32 | 22.1 / 73.4 | 5.08 / 16.9 | 47.7 / 158 |
| Ba-133 | 356.013 | 2.13 / 7.06 | 29.7 / 98.8 | 8.81 / 29.3 | 62.4 / 207 |
Lead, ordinary concrete, steel (pure-iron proxy) and water densities: 11.35, 2.3, 7.874, 1 g/cm³, respectively. Co-60 has two principal lines, shown separately. F-18 and Ga-68 use annihilation photons; Cs-137 uses Ba-137m. Ra-226 excludes daughter emissions. Tl-201 and Yb-169 rows exclude characteristic X-rays.
Used in
The same engine is embedded in The Interaction of Photons with Matter Explained. For charged particles, use the energy-loss calculator.
Cite this
ScienceShot. Photon attenuation calculator. https://scienceshot.com/photon-attenuation-calculator. Use “Copy as citation” above to include your inputs, result and access date.
Sources: NIST XCOM (SRD 8) (cross sections); NIST ESTAR (SRD 124) (densities and compositions); NNDC NuDat 3 / ENSDF (gamma-line energies).
ScienceShot calculation.
Cite this page
ScienceShot. (2026). Photon attenuation calculator [Online calculator]. https://scienceshot.com/photon-attenuation-calculator
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author = {{ScienceShot}},
title = {{Photon attenuation calculator}},
year = {2026},
note = {Online calculator},
url = {https://scienceshot.com/photon-attenuation-calculator}
}