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Research of neutron interactions with the matter under density interactions (DI) up to ~109 cm-2 · s-1, were provided with aim of revelation of possible dependence neutron cross section from DI. The method of research [1] for revelation of such dependence was improved [2]. It consists on transmission asymmetry (TA) of neutrons measurement through of samples pair from different matters. TA was revealed for all pairs containing 235U, in particularly, for pair (235U - Cd) TA consists of (2,541 ± 0,294) ∙ 10-4 that does not contradict to assumption of the cross section dependence from DI. It was defined that correlation related with fission of 235U, and corresponding of relative change of the effective neutron cross section equals ~2,6 ∙ 10-4. Analysis shows that observed depend-ence may be treated as the result of secondary states composition of 235U with anomaly great values of neutron cross section, yield, reduced of possibility radioactive transition and small energy, excited by fragment fission.

Neutrons interaction with matter under high density interactions (DI) was considered. It was shown that un-der neutron cross section measurement with high DI and production as result of interaction neutrons with matter of the second states with great value of such parameters as neutrons cross section, yield and life time probabil-ity of the interaction neutron with matter depends on DI and considered parameters. The expressions, related neutrons transmission, cross section and change of the neutrons transmission through the samples pair from different matters, which simultaneously placed on neutron beam, under the change of neutrons transmission sequence through them (transmission asymmetry) with DI and considered parameters of the second states were obtained. Method for revelation for the cross section change under DI change and improved experimental in-stallation were described.

Application possibility of multiplicity spectrometry for the measurement of direct capture neutron cross section by radioactive samples is considered. For the γ-rays cascade registration on their space distribution in the multisection 4πdetector condition is introduced. It can be seen from calculation results of this condition with combination conditions of coincidence γ-rays cascade in definite time interval and determined energy release in the detector sections which will lead to significant radiation background decrease from research sample radioactive radiation and it influence on registration system. Expected sensitivity for sample minimum quantity under cross section measurement on level 50 b consists ~0,2 mg and sample specific activity~2 ⋅ 1010Bk ⋅ g-1.