Some reaction candidates can be eliminated at once. The D– Li reaction has no advantage compared to p – 5 B because it is roughly as difficult to burn but produces substantially more neutrons through 1 D – 1 D side reactions. There is also a p – 3 Li reaction, but the cross section is far too low, except possibly when T i > 1 MeV, but at such high temperatures an endothermic, direct neutron-producing reaction also becomes very significant. Finally there is also a p – 4 Be reaction, which is not only difficult to burn, but 4 Be can be easily induced to split into two alpha particles and a neutron.