The element boron has two naturally occurring isotopes, 10B and 11B, both of which are stable. It also has 13 radioisotopes which decay through beta and alpha emission or fission.
Boron is found in nature mainly as the mineral borate minerals such as borax, kernite and ulexite. It is a solid at room temperature and a liquid at elevated temperatures. Elemental boron is nontoxic and common boron compounds such as borates and boric acid are also nontoxic. However some of the more exotic boron hydrogen compounds are toxic and require special handling care.
isotope boron-10 is particularly useful in nuclear industry applications because of its high neutron absorption cross section. It is used as a moderator in nuclear reactors to first absorb neutrons and then to dump their energy away from sensitive electronic systems such as integrated circuits.
The isotope 10B is especially good at absorbing thermal neutrons and has been used in radiation shielding and in the therapy known as boron neutron capture therapy (BNCT) to treat tumors in cancer patients. In BNCT, the isotope boron-10 is administered to the patient and then the tumor is bombarded with slow neutrons that will be captured by the atoms of the isotope boron-10, which in turn undergo fission producing a gamma ray and alpha particles.
Both isotopes 10B and 11B have nuclear spin, which makes them useful in nuclear magnetic resonance spectroscopy. The spin splitting of these isotopes causes splitting in the resonances of attached nuclei, providing information about the structure and dynamics of those nuclei.