Which material is considered the best for absorbing neutrons?

Polyethylene is considered the best material for absorbing neutrons due to its composition and hydrogen content. Neutrons interact primarily through nuclear reactions, and materials rich in hydrogen are particularly effective at slowing down (or moderating) neutrons because hydrogen nuclei are of similar mass to neutrons. This interaction leads to elastic scattering, which significantly reduces the energy of fast neutrons, effectively absorbing them.

In contrast, while concrete, lead, and steel can provide some degree of neutron shielding, they are not as efficient as polyethylene. Concrete may contain hydrogen in the form of water, but its other components, like silica and minerals, do not contribute as effectively to neutron attenuation. Lead, although a dense material, is primarily effective at absorbing gamma radiation rather than neutrons. Steel also has limited effectiveness for neutron absorption compared to materials with high hydrogen content. Therefore, polyethylene stands out as the superior choice for neutron shielding due to its effectiveness in moderating and absorbing neutrons.