Photon shielding relies on dense, high-atomic-number materials: lead, tungsten, bismuth, tin, antimony, barium and rare-earth elements, often in polymer composites; concrete and steel for buildings; lead glass or lead acrylic where viewing is needed. Neutrons need hydrogen-rich and boron-containing materials. The right choice depends on energy, required attenuation, weight, form and environment.
Reviewed 2026-09-24
Common materials compared
| Material | Strengths | Limitations | Typical use |
|---|---|---|---|
| Lead sheet, lead rubber | High density (11.34 g/cm³), well-characterized, economical | Heavy; toxic; controlled recycling required | Garments, room shielding, containers |
| Lead-free polymer composites | Flexible; elements with different absorption edges can be combined | Performance depends on formulation and energy; compare under identical conditions | Garment cores, drapes, curtains |
| Tungsten | Very dense (19.3 g/cm³) | Costly; hard to form | Collimators, compact shields |
| Concrete, barite concrete, steel | Structural; economical at large scale | Thick and heavy | Imaging rooms, radiotherapy bunkers |
| Lead glass, lead acrylic | Transparent | Contain lead; lower attenuation per thickness than lead sheet | Viewing windows, barriers, eyewear |
| Polyethylene, water, borated materials | Slow and capture neutrons | Little use against photons on their own | Neutron sources, reactors |
Densities are standard handbook values. Performance of any product must be taken from its own test report at stated conditions.
Why combine elements?
Every element absorbs most strongly just above its absorption edge and less so just below it. Lead’s K-edge is at 88 keV, so it absorbs relatively weakly between about 40 and 88 keV, where much of a diagnostic scatter spectrum lies. Elements such as tin, antimony, barium and gadolinium have edges in that range, which is why multi-element lead-free formulations are designed around a target spectrum.
The same reasoning explains why a lead-free material can match lead at one tube voltage and differ at another: lead equivalence must always be stated with its test condition.
How lead equivalence is determined
- Same radiation quality (tube voltage, filtration) and the same measurement geometry for both paths.
- The material sample under test.
- A lead reference whose thickness d is adjusted.
- Transmission is measured at the same detector position.
- When transmission matches, the material’s lead equivalence is d mmPb. It is not the material’s own thickness, weight or lead content.
References
- NIST XCOM: Photon Cross Sections Database
- X-Ray Data Booklet, Lawrence Berkeley National Laboratory (electron binding energies)
- NCRP Report No. 147 (2004): Structural Shielding Design for Medical X-Ray Imaging Facilities
- Bushberg et al., The Essential Physics of Medical Imaging, 3rd ed., 2012
- IEC 61331-1:2014 / IEC 61331-3:2014 Protective devices against diagnostic medical X-radiation
This encyclopedia is for general and engineering reference and is not medical advice. Consult radiation protection or medical professionals for individual exposure assessment.