Li-7 is used to control the pH level of the coolant in the primary water circuit of pressurized water reactors. Li-7 is also used for the production of the medical research radioisotope Be-7. Li-6 is used in thermonuclear weapons and the export and use of Li-6 is therefore strictly controlled. Li-6 can also be used for the production of the radioisotope H-3, which is used in biochemistry research.