At the present time considerable attention is being paid to the monitoring of energy release in the cores of nuclear reactors for various purposes [i]. Exact and reliable measurement of the neutron fields in reactor cores requires continuous improvement of old experimental methods and development of new ones. In-reactor measurements, however, always entail certain difficulties due to the difficult radiation and thermal conditions under which the detectors must operate, etc. In recent years there has been a great development of instrumental methods of measuring neutron fields, methods in which small fission chambers, electron-emission neutron, self'powered probes, thermal-neutron probes, etc. are used as the primary probes [2-5].