Nanovia Flex B4C : Neutron capture

The risks of free neutrons

When a free neutron hits a person, it’s able to modify/destroy the DNA of a molecule. Since the neutron does not have a charge, they are not easily slowed down by the other atomic elements, and can penetrate through a lot of material before hitting another atom’s core.

How B4C captures free radicals generated by nuclear fission

The boron present in the ceramic B4C, Is a metalloid of which several isotopes exist, Meaning that these atoms have the same number of protons but a different number of neutrons.

Boron-10 in particular has a very wide core absorption cross section. When a free neutron, generated by nuclear fission encounters boron-10, this wide core absorption cross section effectively functions as a big net. This makes boron-10 much more likely to get hit than other atoms.

This impact creates an predominantly unstable isotope of Boron-11 that fissures into :

• An alpha particle (helium atom without electrons)
• A lithium-7 atom
• Gamma radiation

¹⁰B + nth → ⁴ He²⁺ + ⁷Li ³⁺ + 2.79 MeV (6%)

¹⁰B + nth → ⁴ He²⁺ + ⁷Li ³⁺ + 2.31 MeV + γ (0.48 MeV) (94%)

Source : Caractérisation de champs neutroniques rapides et épithermiques pour thérapie par capture neutronique basée sur accélérateur / Marine HERVE

The two elements generated are not radioactive, the gamma radiation is absorbed by the other elements as it passes through them. Shielding made out of heavier elements such as lead allows for a quicker absorption.

These properties make boron-10, in its solid form (Boron carbide) and its liquid form (Boric acid), used as a regulator (neuron poisons) in nuclear reactors. By inserting boron-10 when required, the liberated neurons by the fission of uranium-235 are intercepted, neutering the chain reaction.