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

A procedure is considered for extracting the energy value of a virtual singlet proton–proton state from experimental data. A preliminary value of Epp in the d + 1H → p + p + n reaction at a deuteron energy of 15.3 MeV is obtained from a comparison of experimental data and simulation results.

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.

An experiment was proposed to determine the low-energy parameters of the np interaction in the nd breakup reaction at a neutron energy of 5 MeV in the RADEX neutron channel, Institute for Nuclear Research, Russian Academy of Sciences, Moscow, Russia. The energy of the virtual 1S0 state and the np scattering length can be obtained from the experimental dependence of the reaction yield on the relative energy of motion of the breakup neutron and proton in the kinematic region, where the np interaction in the final state is most pronounced. The reaction events were simulated, based on which the optimal conditions for the future experiment were selected.

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.

The authors offer works using the MMF INR RAS neutron channel to study the cluster structures in light nuclei, in particular, 𝛼-4n-𝛼 and 8Be-4n in the highly excited state 12Be*. This needs the registration of charged particles from the 12Be* 𝛽-decay during its formation in the 𝑛+13C reaction in the intervals between cascade neutron pulses. The paper presents the first results of an experiment on measuring the spectra and time distributions of gamma-quanta and neutrons using a proton beam of 50 Hz and a duration of 0.3 𝜇s.

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 authors consider a way of determining the energy of the singlet quasi-bound pp-state in d + 1H → n + p + p reaction. The acquisition of experimental data from measuring the length of pp-scattering is described, along with extracting the energy of the proton–proton state from experimental data according to the χ2 minimum.

The paper presents the results of test measurements to determine the possibilities of studying the cluster structure of highly excited states of the 6Li nucleus in the 6Li(𝑛, 3He 𝑛) 3H reaction on the RADEX neutron channel of the Institute for Nuclear Research of the Russian Academy of Sciences. In the experiment, scattered neutrons were detected in coincidence with the decay products of highly excited states (helium-3). The first experimental data on the excitation energy of the 6Li nucleus have been obtained.

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 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 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.

Kinematics of the 13 C( n , 2 p ) 12 Be* reaction are modeled using cascade neutrons with energies of 30–150 MeV. The correlation is considered between the decay of excited states of a 12 Be cluster with α-4 n -α and 8 Be-4 n quasi-molecular structures at energies of excitation up to 25 MeV. The possibility is shown of measuring parameters of the decay channels of the excited state of 12 Be with 4 n correlation registered in the coincidence of a 2 p pair and α particles from cascade neutrons of the RADEX pulsed source.

A prototype of an experimental setup is created to test the possibility of detecting coincident charged particles and neutrons in the RADEX neutron channel at the Institute for Nuclear Research. Test measurements are made of the n + 6Li → α + d + n reaction, demonstrating the possibility of detecting coincident charged particles and neutrons, along with identifying the type of charged particle.

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.

The feasibility of monitoring maximum energy of neutrons $$E_{{\text{n}}}^{{\max }}$$ in the neutron flux from a source by analyzing pulse-height spectra from a 10B detector is investigated. Ionization losses of 4He and 7Li nuclei in two detector gaps are modeled. The clear experimental dependence of the position of the maximum and the shape of these spectra on $$E_{{\text{n}}}^{{{\text{max}}}}$$ and calculations in agreement with this dependence can be used to monitor the maximum energy of neutrons.