When one material isn't enough
Reactor environments, neutron sources and accelerator facilities often produce both neutrons and gamma rays. Tungsten is excellent against photons but does little to neutrons. Boron carbide absorbs thermal neutrons but does little to photons. Mixed fields call for both.
Ordering the layers
- Moderate fast neutrons with a hydrogen-rich material, such as polyethylene or water, if the source produces them.
- Absorb the slowed neutrons with Rapid 3DShield Boron Carbide. A few millimetres at 100% infill absorbs nearly all of a thermal beam (calculated).
- Stop photons with Rapid 3DShield Tungsten. This covers source gammas and the 0.48 MeV gamma ray that boron-10 gives off in most neutron captures.
Neutron capture in many materials produces secondary gammas, so placing tungsten after the neutron absorber is usually the better arrangement. Your geometry and source may change that. Model or measure before you commit.
Building a layered part
- Nested prints. Print each material separately and nest them, for example concentric sleeves or a shell with an insert. Design overlaps or steps at the joints so there's no straight-through gap.
- Multi-material printing. Printers with two toolheads can print both in one job. Remember the different nozzle recommendations: 0.8 mm for tungsten, 0.6 mm for boron carbide, both hardened steel.
Verify
Attenuation of separate layers multiplies. Real fields with scatter and mixed energies need measurement, so confirm the finished assembly with appropriate detectors and have your Radiation Safety Officer sign off.
Working on a shielding program or ordering by PO? Email [email protected]. · Tungsten filament · Boron carbide filament