[en] This paper deals with the design and basic characteristics of an ion gun emitting Li⁺, Na⁺ and K⁺ ions. The operation of a thermoionic ion source is based on the effect of thermoionic emission of alkali ions from the corresponding aluminosilicate. The source proved to operate satisfactorily in UHV systems. The lifetime of the source is above 300 h, in which time emission decreases steadily for approximately an order of magnitude. Mass spectrometric studies of the ion beam content have revealed only the presence of Na⁺, ³⁹K⁺ and ⁴¹K⁺, when the source operates with an Na₂O.Al₂O₃.2SiO₂ emitter. The energy spread of Na⁺ ions emitted from the same substance is 0.3 eV approximately. (Auth.)