linguistic:voice_change
Nuclear properties

Naturally occurring beryllium, save for slight contamination by the cosmogenic radioisotopes, is isotopically pure beryllium-9, which has a nuclear spin of 3 / 2. Beryllium has a large scattering cross section for high-energy neutrons, about 6 barns for energies above approximately 10 keV. Therefore, it works as a neutron reflector and neutron moderator, effectively slowing the neutrons to the thermal energy range of below 0.03 eV, where the total cross section is at least an order of magnitude lower; the exact value strongly depends on the purity and size of the crystallites in the material.

The single primordial beryllium isotope Be also undergoes a (n,2n) neutron reaction with neutron energies over about 1.9 MeV, to produce Be, which almost immediately breaks into two alpha particles. Thus, for high-energy neutrons, beryllium is a neutron multiplier, releasing more neutrons than it absorbs. This nuclear reaction is:

Neutrons are liberated when beryllium nuclei are struck by energetic alpha particles producing the nuclear reaction

where He is an alpha particle and C is a carbon-12 nucleus. Beryllium also releases neutrons under bombardment by gamma rays. Thus, natural beryllium bombarded either by alphas or gammas from a suitable radioisotope is a key component of most radioisotope-powered nuclear reaction neutron sources for the laboratory production of free neutrons.

Small amounts of tritium are liberated when Be nuclei absorb low energy neutrons in the three-step nuclear reaction

He has a half-life of only 0.8 seconds, β is an electron, and Li has a high neutron absorption cross section. Tritium is a radioisotope of concern in nuclear reactor waste streams.