Silicon boride as boron silicide was discovered in 1900 when a mixture of Si and B were melted.After this report, there were many reports about silicide (stable compounds) such as B3Si and B6Si (besides, B12Si).After that, SiB4 (rhombohedral crystal structure) and SiB6 (orthorhombic crystal structure) are recognized with the stable compound ad silicon boride, SiB4, SiB6, SiB6-x, SiB6+x, Si11B31.Then, SiB6 is a prospective material for use as a thermoelectric semiconductor, and has high hardness, moderate melting point, and low specific gravity.As for natural boron, it has two naturally occurring and stable isotopes, boron 11 (11B) and boron 10 (10B).The neutron absorption 10B is included about 19-20% with 81-80% 11B.Boron is similar to carbon in its capability to form stable covalently bonded molecular networks.The mass difference results in a wide range of d values between the 11B and 10B.The 10B isotope, stable with 5 neutrons is excellent at capturing thermal neutrons.For example, it is possible to decrease a thermal neutron required for the nuclear reaction of uranium 235 (235U).If 10B absorbs a neutron (1n), it will change to 7Li + 4α (α ray, similar with a 4He) with prompt γ ray from 11B (equation 1).