An experiment was carried out at the RADEX neutron channel of the Institute for Nuclear Research, Russian Academy of Sciences, at neutron energies of 40–60 MeV to investigate the cluster structure ^3He+t of ^6 Li nucleus in the reaction ^6 Li( n ; ^3 He n ) t . The excitation energy spectrum of ^6 Li was obtained in the range E_x=16-50 MeV. At an excitation energy of E_x=16.6 MeV a resonance with Γ=0.7 MeV was observed, and in the interval E_x=30-50 MeV two broad resonances were found at E_x=35.9 and 43.1 MeV with Γ=8.4 and 5.4 MeV, respectively. All levels are observed for the first time.

We presented a setup created on the RADEX neutron channel at the Institute for Nuclear Research of the Russian Academy of Sciences to study the properties of highly excited states of light nuclei. The first experiment was carried out on the setup to determine the cluster structure of highly excited states of the 6Li nucleus in the reaction 6Li(n, 3He n)3H at a neutron energy of 50 ± 5 MeV. Several variants of the data collection system have been tested. A preliminary spectrum of the excitation energies of the 6Li nucleus has been obtained.

Multiwire position-sensitive neutron detector with two layers of boron-10 has been developed to detect both thermal and fast neutrons. Sensitive dimensions of two coordinate neutron detectors are 50 × 50 mm. New detector characteristics are compared with those of a 100 × 100 mm detector built earlier which we used in neutron flux spatial distribution measurements. Plane-parallel design of the new detector has symmetrical structure with respect to wire anode and also includes two intermediate grids and two cathodes made of parallel wires with 2 mm pitch and two silicon substrates coated with boron-10 layers of 0.003 mm thickness. Detector geometry and working gas mixture and pressure are chosen so as to ensure full absorption of secondary alpha particle from reaction with thermal neutron within detector gas medium half thickness. Neutron coordinates are determined from measured ionization loss pulse heights produced by secondary nuclei. The detector expected efficiency to thermal neutrons is about 5

The distributions of intermediate and slow neutrons from the outlet collimated channel of a photoneutron source are measured. A significant difference is observed between the shapes of the distributions of two groups of neutrons with energies above and below the cadmium cutoff. Whereas the distribution of intermediate neutrons has a symmetrical Gaussian shape, the distribution of slow neutrons has a complex shape. The possible causes of the difference between these shapes are discussed.

A position-sensitive detector, which is a neutron target at the same time, is presented to study the interaction reactions of fast neutrons of above 1 MeV with light nuclei, in particular, with the 10B nucleus. It contains two boron-10 layers and a system of wire electrodes to identify secondary nuclei, in particular 3H and 4He, and to determine energy loss and departure angle. Thus the neutron energy can be determined.

To study the cluster structure of light nuclei in the reactions of interaction of fast neutrons with the 9Be nucleus, the kinematics of the reactions n + 9Be → α + 6He and n + 9Be → 8Be + 2n → 2α + 2n at energies of 1–3 MeV were modeled. It was shown that the characteristics of reaction channels in the interaction of a neutron with a 9Be nucleus can be found by measuring the ionization losses of charged reaction fragments in a multilayer gas-filled charged particle detector with a beryllium converter.

An ionization loss simulation in several sequent gaps of the neutron detector is performed. It is based on the boron-10 rigid layer converter and gaseous chamber. It was shown that the distribution of ionization losses over gas gaps varies significantly depending on the incident neutron energy. The fact can be used to control the energy of the neutron flux using this detector.

Значение \({}^{1}S_{0}\) np -длины рассеяния получено в кинематически полном эксперименте по исследованию реакции nd -развала при низких энергиях нейтронов канала РАДЭКС ИЯИ РАН. В эксперименте два нейтрона детектировались по разные стороны от направления первичного пучка. Полученные из сравнения экспериментальной зависимости выхода реакции nd -развала от относительной энергии np -пары с результатами моделирования значения \(a_{np}={-}25.9\pm\) 1.1 Фм при \(E_{n}=9\) МэВ и \(a_{np}={-}25.1\pm 1.3\) Фм при \(E_{n}=11\) МэВ существенно отличаются от значения, полученного в эксперименте по свободному np -рассеянию, что свидетельствует об эффективном усилении np -взаимодействия в присутствии третьего нуклона.

The ^1S_0 np scattering length was obtained in a kinematically complete experiment devoted to studying the nd -breakup reaction at low energies of neutrons from the RADEX channel of Institute for Nuclear Research, Russian Academy of Sciences. In this experiment, two neutrons were detected on different sides of the primary-beam axis. The scattering-length values of a_np=-25.9± 1.1 fm and a_np=-25.1± 1.3 fm obtained at E_n=9 and 11 MeV, respectively, from a comparison of the experimental dependence of the nd -breakup reaction yield on the relative energy of the np pair with the results of a simulation differ significantly from the corresponding values found in an experiment that studied free np scattering. This is indicative of an efficient enhancement of np interaction in the presence of a third nucleon.

A study is performed of the directional sensitivity of a two-coordinate neutron detector based on a 3 μm 10B layer and a wire chamber. The suppression of scattered neutron detection by the detector is observed, relative to data from the 3He counter. This is explained by strong absorption of neutron flux in the 10B layer when it is incident at a large angle to the plane of the detector, and by the energy of the 4He or 7Li secondary nucleus being insufficient to exceed the threshold energy if the nucleus is produced immediately after entering the 10B layer.

A study is performed of the branching ratio of the ground and excited states of 7Li nuclei emitted in interactions between neutrons and 10B nuclei at energies above 1 MeV. A neutron detector based on a 10B layer serves as both a target and a cathode of the wire chamber for recording ionization losses of secondary nuclei. The branching ratio of reactions n + 10B → 7Li + 4He and n + 10B → 7Li + 4He + γ is found by analyzing the amplitude spectra from two detector gaps and modeling the ionization losses of 4He nuclei with allowance for the kinematics of both reactions.

A kinematically complete experiment devoted to studying the $$nd$$ -breakup reaction at energies of 8 and 11 MeV via detecting all three secondary particles was performed. The $${}^{1}S_{0}$$ neutron–neutron ( $$nn$$ ) scattering-length values of $$a_{nn}={-}19.8\pm 0.4$$ and $${-}19.0\pm 0.5$$ fm at, respectively, $$E_{n}=8$$ and $$11$$ MeV were obtained from a comparison of the experimental dependence of the yield of the $$nd$$ -breakup reaction on the relative energy of the $$nn$$ pair with the results of a simulation. An analysis of the values obtained for the $$nn$$ scattering length, together with data from other experiments, confirms the hypothesis that three-nucleon forces affect the parameters of $$nn$$ interaction that are extracted from reactions involving few-nucleon systems and gives a new asymptotic $$nn$$ scattering length, $$a_{nn}={-}16.1\pm 0.1$$ fm.

A system of two low threshold-energy air ionization chambers 3 mg cm −2 thick is created. The system includes a new two-gap chamber that has a sensitive area of 113 cm 2 , 1 mm gaps between electrodes made of polyimide films 3 µm thick, and a multichannel chamber. The contribution to the dose from recombination, low-energy protons, and δ-electrons is investigated. The total radiation dose of the system is 5 Mrad.

The results of Monte Carlo simulation and test reflectometry experiments on the "Gorizont" neutron reflectometer (on the IN-06 pulsed neutron source at INR RAS) after its upgrade with a two-dimensional detector with a positioning system are presented. The two-dimensional detector makes it possible to use the instrument not only for neutron reflectometry, but also for small angle neutron scattering. Estimates of the instrument resolution and the spectra of the neutron beam at different collimations have been obtained using Monte Carlo simulation. Test reflectometry experiments have been performed on mirrors with known characteristics. The characteristics match the manufacturer's data with an error of 5%, obtained from the simulation.