The construction and characteristics of a pulsed monoenergetic soft X-
ray source (E = 0.848 keV) are presented. The source is based on the p
rinciple of conversion of the X-ray radiation emitted from a heavy-cur
rent discharge of plasma focus, and allows obtaining a ''spectral puri
ty'' of the emitted radiation close to 100%. The radiant flux density
is about 10(17) photon/(cm(2) s), which is sufficient for the calibrat
ion of X-ray detectors with sensitivities not lower than about similar
to 10(-19) (C cm(2))/photon.