In the 1960s appreciable success was achieved in the investigation of the condensed state of matter with the aid of neutrons. It was shown convincingly that the method of inelastic scattering of slow (energy less than 1 eV) neutrons has indisputable advantages over other methods for studying the behavior of atoms and molecules in solids and amorphous and liquid bodies.Work in this direction started at the Physics and Power Engineering Institute (PPEI) in the first half of the 1960s when a group of enthusiasts, including V. G. Liforov, V. A. Parfenov (group leader), and V. A. Semenov, initiated the development, on the IBR-I pulsed fast reactor at the Joint Institute of Nuclear Research, a double time-of-flight slow-neutron spectrometer, later called DIN. The idea for such a spectrometer was proposed by I. I. Bondarenko, V. V. Orlov, V. A. Parfenov, and V. F. Turchin. The first variant of multiangle spectrometer DIN-I was produced in 1966 and was followed by an improved variant DIN-1M after the IBR-I reactor was reconstructed. In connection with the construction of the new pulsed reactor IBR-2, a complex of spectrometers DIN-2K, including DIN-2PI and DIN-2PR, was developed; the first of these spectrometers started operation in 1983 and the second in 1985. Both spectrometers operate effectively today.At all stages of the development of the spectrometers and the performance of experimental investigations on them, the work was actively supported by the scientific leadership of the PPEI, A. DIN Type Spectrometers. These spectrometers are double time-of-flight direct-geometry spectrometers with a mechanical interruptor. Such spectrometers were the first type of double spectrometers operating on pulsed neutron sources [1]. The reason is that their functional scheme is simple and logical, there are no additional background effects, and the interpretation of the results is physically obvious. The possibility of using wide ranges of scattering angles and initial neutron energies determines their main advantage: acquisition of experimental data in a wide range of dynamical variables of the scattered neutron (momentum and energy transfers) [2]. Figure 1 displays the overall layout of the DIN-2PI spectrometer [3].Measurement and Estimate of the Double Differential Scattering Cross Sections of Reactor Materials. Investigations of the atomic-molecular dynamics of reactor materials by the slow-neutron scattering method are important for obtaining estimated scattering characteristics (double differential, total, differential scattering cross sections, and so on), which determine all basic parameters of a neutron-physical setup. At the initial stage of development of the method, obtaining such constants was the main problem of the method, which allowed for rapid improvement and dissemination.In a constants program formulated in the mid-1960s, the effect of inaccuracies of the dynamic model of moderators (for the example of beryllium and zirconium hydride) on the scattering characteristics and the reactor-physical functionals of the...
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