A statistical analysis is performed of the results on the determination of the critical neutron fluence in MR, SM-2, and BOR-60 with different irradiation temperature. It is shown that the critical neutron fluence depends Not only on the irradiation temperature but also, and to a even greater extent, on the radiation composition Factor (ratio of the neutron and γ-ray flux densities). Thus the critical neutron fluence for irradiation at 600 deg. C In MR (radiation composition factor 0.13) is 17.10~21 cm~-2 and in SM-2 (radiation composition factor 0.1) 11.10~21 cm~-2 at the same temperature.
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