Lithium

⁷Li, as hydroxide monohydrate (⁷LiOH•H₂O), is used to maintain the pH level of the coolant used in pressurized water reactors in the nuclear power industry [39], [40]. Lithium plays a role in the construction of a thermonuclear bomb, which differs from a fission weapon in that it uses the energy released when two light atomic nuclei (i.e. deuterium (²H) and tritium (³H)) fuse to form helium and a high energy neutronvia this DT reaction. ⁶Li is used, in the form of ⁶Li deuteride (⁶Li ²H), as fusion fuel capable of producing tritium when bombarded with neutrons within the weapon via the reaction ⁶Li (n, ³H) ⁴He [41]. Li-based laboratory reagents have found their way into surface water and can be easily identified. Although a military secret in the 1950s, it is now known that substantial amounts of ⁶Li (normally having an isotopic abundance of 0.076) were removed from chemical reagents to be used in nuclear weapon development. Reagents containing the remaining lithium depleted in ⁶Li (having an isotopic abundance as low as 0.025) were sold to both chemical manufacturers and to laboratory chemists for their use [42]. The distinctive isotopic signature of depleted ⁶Li, having a n(⁷Li)/n(⁶Li) ratio of 39, compared to a ratio of 12 in naturally occurring terrestrial materials, enables easier detection of this lithium source in polluted waterways and the environment [35], [37].

⁷Li is a decay product of the ¹⁰B (neutron, alpha) ⁷Li reaction, which has a peak value for room temperature neutrons. Brain tumor cells are typically found some 5 to 7 cm below the surface of the skull. After ¹⁰B has been introduced to or entered the tumor cells, a beam of neutrons of energy slightly above room temperature is introduced to the affected areas. The energy of these neutrons is reduced to room temperature by the time they react with the ¹⁰B, which then disintegrates into high energy charged particles (⁷Li and ⁴He), which deposit their kinetic energy in nearby (predominately cancerous) cells and destroys them. Any adjacent normal cells are unaffected [43].