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Analysis of the emission of delayed neutrons (the E-decay energy of the precursor nucleus of the delayed neutrons and the binding energy of a neutron in a daughter emitter-nucleus are compared) shows that approxunately 271 fission products can be treated as possible precursor nuclei [1]. Experimental investigations have yielded information about the probability of emission of delayed neutrons for 83 of the precursor nuclei as a whole and six in the isomeric state [2]. At the same time, the six-group representation of the characteristics of delayed neutrons, such as the relative yield, the half-life of their precursors, and the energy spectra, has proven itself well in many practical applications. The six-group representation of the characteristics was first introduced at the early stages of the research [3] and it is now known that it gives an average picture of the process of emission of delayed neutrons accompanying fission of heavy nuclei by neutrons. Nonetheless, analysis of the experimental data in the six-group representation is an effective tool for investigating the emission of delayed neutrons. The data obtained with this approach make it possible to analyze model representations of the mechanism of emission with different excitation energy of the fissioning nuclei. In addition, they are important for practical applications.In the present work, in contrast to previous measurements [1], we were able to decrease substantially the time between the end of irradiation and commencement of the delayed-nentron count. The measurements were performed on the apparatus based on the electrostatic accelerators at the Main Science Center of the Russian Federation --Physics and PowerEngineering Institute [5].The experimental method is based on cyclic irradiation of the fissioning sample by neutrons from an accelerator target followed by measurement of the decay of the delayed-neutron intensity of a 4r detector. The count rate as a function of time was measured using a multiscalar counter with a variable time channel. Measurements with different irradiation times of the sample and different counting times of the delayed neutrons were performed in the experiment. This procedure made it possible to increase the relative yield of delayed neutrons corresponding to definite groups of precursor nuclei in the integral curve of the decay of neutron activity and thereby to increase the reliability of the parameters determined.A block diagram of the apparatus is presented in Fig. 1. The reactions T(p, n)3He and D(d, n)3He served as sources of monoenergetic neutrons. The tritium and deuterium targets were irradiated by a beam of accelerated protons or deuterons in a KG-2.5 cascade generator. The energy distribution of the neutrons from the accelerator target was recorded with a 3He spectrometer. The main recording element of the delayed-neutron detector consisted of a standard SNM-11 counter with l~ enrichment to 80%, operating in a proportional mode at a voltage of 650 V. It consisted of an assembly of 30 SNM-11 counters, d~tribu...

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