[en] Study of delayed neutrons is reviewed, and the mechanism, precursor and other information of delayed neutron emission are studied. The energy spectra of delayed neutrons are shown in figures. The ISOL systems installed at various reactor facilities have been used for the study of delayed neutron emission. Those are ISOL at Juelich, the TRISTAN at Iowa State University, the SOLIS at Soreq, OSIRIS at Studvik, and LOHENGRIN at Laue-Langevin Institute. By using the ISOL systems, data on the precursors of delayed neutron emitters will be obtained for respective nuclides. The nuclear structure of the precursors may be known. The intensity of separated beam of the isotope separators must be strong. The expected intensity of the KUR-ISOL, which is being planned at Kyoto University Reactor Institute, is estimated. Neutron detectors with good efficiency must be prepared. Moving tape collectors for beam collection are explained. Reduction of background counts can be done by the coincidence measurement of neutrons and beta-ray. Neutron detectors for the present purpose are BF₃ counter, He³ proportional counter, ionization chamber, Li⁶ glass scintillator, and others. The time-of-flight method is used for the spectrum measurement. (Kato, T.)