 The single primordial beryllium isotope 9Be also undergoes a ( n , 2n ) neutron reaction with neutron energies over about 1 @.@ 9 MeV , to produce 8Be , 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 : 
