What a shield actually has to stop
"Put heavy material in the way" works for some radiation and fails for others. Choosing the right Rapid 3DShield material starts with knowing what you're blocking.
X-rays and gamma rays
Photons have no charge and no mass. They are removed from a beam mainly by three interactions:
- Photoelectric absorption dominates at low energies and rises steeply with atomic number (Z). This is where tungsten excels.
- Compton scattering dominates in the mid-MeV range. It depends mostly on how many electrons lie in the path, which means how much mass per unit area.
- Pair production matters above about 1.02 MeV and also increases with Z.
Photon attenuation is exponential. Each half-value layer (HVL) cuts intensity in half, and the HVL depends on both photon energy and the density of the shield. Because a printed part is less dense than solid metal, it needs proportionally more thickness. Rapid 3DShield Tungsten at 7.8–9.2 g/cc needs roughly 2.1–2.5× the thickness of solid tungsten (19.3 g/cc) for the same mass per unit area. Use our measured green-state test data rather than handbook values for solid metal.
Neutrons
Neutrons carry no charge, and heavy nuclei barely slow them. Shielding them takes two steps:
- Moderation. Fast neutrons lose energy fastest by colliding with light nuclei, especially hydrogen in water and plastics.
- Absorption. Once slow, neutrons are captured by strong absorbers. Boron-10 (19.9% of natural boron) has a thermal cross-section of about 3,840 barns: ¹⁰B + n → ⁷Li + ⁴He + 2.79 MeV.
Rapid 3DShield Boron Carbide is built for the absorption step. At mid-spec loading, its calculated thermal-neutron mean free path is about 0.4 mm.
Distance and time still matter
For a small source, dose falls with the square of distance. Double the distance and dose drops to a quarter. Shielding works alongside distance and exposure time, not instead of them. Have your Radiation Safety Officer confirm the final design with measurements.
Working on a shielding program or ordering by PO? Email [email protected]. · Tungsten filament · Boron carbide filament