Boron is a relatively common element with two stable isotopes. Boron-10 and boron-11 differ in the number of neutrons in their nuclei, which leads to slightly different chemical and physical properties.
Both boron isotopes are used extensively in the nuclear industry. B-10 is found in boric acid as a chemical shim in pressurized water reactors and in sodium pentaborate for backup liquid control systems in boiling water reactors. Both boron isotopes can reflect neutrons and produce the radioisotopes C-11 and N-13. Outside of the nuclear industry both boron isotopes serve as food labels to analyze boron metabolism and are used in so-called boron neutron capture therapy (BNCT) to kill malignant tumor cells.
In BNCT, epithermal neutrons emitted from the fission reaction 10B(n,a)7Li are captured by boron-10 atoms in the target tissue to produce the linear recoiling particles 4He and 7Li. These particles penetrate tissues with a range of 5-9 mm and deposit large amounts of ionizing radiation within the cancerous cells, which delivers a lethal blow.
Hexagonal boron nitride (h-BN) has attracted much interest because of its exceptional physical properties, such as ultrahigh energy band gap and layered structure, strong optical transitions near the band edge, high electrical resistivity, and large thermal neutron capture cross section. Recent progresses include the growth of freestanding h-BN epilayers with large thicknesses, understanding the vertical and lateral transport properties and realization of h-BN thermal neutron detectors with unprecedented detection efficiencies.