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.

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 method of testing of threshold SiO2 aerogel Cherenkov detectors using cosmic radiation is described. The method requires a minimum amount of additional electronics and does not involve massive absorber layers (e.g., lead). The method makes it possible to directly take into account the threshold in determining the efficiency of the detectors under study and to test their operation in different energy ranges for relativistic charged particles. Good agreement between the results of the simulation and measurements was obtained.

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.

The authors discuss problems of studying the yields of the reactions 13 C(γ, p ) 12 B, 14 N(γ, 2 p ) 12 B, and 14 N(γ, 2 n ) 12 N with ( 12 B, 12 N) activity measured by the telescopes of Δ E detectors in the intervals between electron accelerator pulses. The fluxes and spectra of irradiating bremsstrahlung γ-quanta are found for chosen radiators and targets. The effect the parameters of targets and telescopes of Δ E detectors have on the production of ( 12 B, 12 N) nuclei and the registration of their decay is estimated.

A structural configuration and parameters of a modernized source of electrons and gamma quanta with energy of 4–10 MeV are presented. The source is designed on the basis of electron linac LUE-8-5 RV (INR RAS) and can be used for detector calibration and other practical applications.

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.

In this article, we describe an experimental verification of the correctness of registration of delayed neutrons from 238U photofission at a maximum energy of 10 MeV of bremsstrahlung γ quanta on a pulsed linear electron accelerator LUE-8-5 in an interval of (1–5) ms after each beam pulse at times ≳7 min from the onset of irradiation. The measurements have been carried out using the scintillation spectrometer of fast neutrons based on a single stilbene crystal with pulse shape discrimination of γ quanta and fast neutrons. The temporal dependence of the counting rate of delayed neutrons in 238U photofission has been measured at a repetition rate of 300 s–1 in a time interval of (1.25–3.30) ms after the beam pulse.

A study is performed of distortions in the registration of fluxes and energy spectra of delayed neutrons by a stilbene scintillation spectrometer inside Pb shielding. The delayed neutrons are products of 238 U photofission on a pulsed electron linear accelerator. The dependences of these distortions on the neutron energy and wall thickness of the Pb shielding are considered. Contributions from processes in the walls of the irradiation hall are described.

Conditions are considered that allow the separation of a hypothetical short-lived component (T1/2 = 1 ms) in delayed neutrons from 238U photofission on a pulsed linear electron accelerator when neutrons are detected during intervals between beam pulses using a stilbene scintillation spectrometer with pulse shape discrimination of background γ-quanta scintillations.

A procedure for measuring the rhenium content in radioactive ore rocks is tested. Samples of rhenium-containing rocks are irradiated with neutrons from a photoneutron source. Analysis of activation gamma spectra shows that rhenium can be identified against a background of accompanying elements, making neutron activation analysis an effective way of determining rhenium content.

An experiment to study total nuclear photoabsorption cross sections at the linear electron accelerator LUE-8-5 (INR, RAS) in the photon energy region of 5–10 MeV called the pygmy resonance is simulated. The motivation for the experiment is new experimental data on photoexcitation of spin isomers of medium-heavy nuclei, which indirectly indicate a change in multipolarity of near-threshold photoabsorption of nuclei. The experiment implies direct investigation of the observed effects by measuring total photoabsorption cross sections in the photon beam. The simulation is performed using the GEANT-4 code. The parameters of the facility are optimized, and the choice of the detectors for the measurements is substantiated.

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.

A two-coordinate 10B detector is used to study the spatial distribution of a neutron flux with maximum energies $$E_{{\text{n}}}^{{{\text{max}}}}$$ = 3.3–5.1 MeV from the outlet channel of a photoneutron source. The maximum of neutron flux intensity measured along the horizontal axis is found to shift backward, relative to the direction of the primary electron beam upon an increase in maximum neutron energy $$E_{{\text{n}}}^{{{\text{max}}}}$$ .