[en] Definition of the content of rare metals in the samples of ore was carried out by the method of the neutron activation analysis. IREN installation which represents the linear electron accelerator and no multiplying tungsten target served as the neutron source. The tungsten target has been located in the centre of the water moderator in diameter 15 cm.The irradiation has been spent on installation IREN within 8 hours 40 minutes. Electron energy was an order of 30 MeV, a current of an order 5 -10 microamperes. Samples settled down on the moderator surface. 2 samples of ore have been irradiated: Os-1 (m = 1.172 g), and Os-2 (m = 1.291 g) and a number of indicators for definition of neutron flux. Weights of indicators did not exceed a several milligrams.

[en] The results of measurements of the fission cross-sections and resonance parameters σ₀Γ_f and Γ_f of ²³⁴U and ²³⁷Np together with the preliminary results of ²⁴³Am fission cross-section measurements carried out in the framework of the program of studying subthreshold fission at the IBR-30 pulsed neutron source in Dubna are presented. The measurements were conducted by the time-of-flight technique. Fission events in ²³⁴U and ²³⁷Np were detected by two multisectional ionisation chambers containing ²³⁴U (about 100 mg) and ²³⁷Np (about 1.5 g) highly purified from isotopes with a large fission cross-section, such as ²³⁵U and ²³⁹Pu. Each chamber also contains a ²³⁵U target for neutron flux measurements. ²⁴³Am cross-section measurements are conducted with a back-to-back ionisation chamber containing about 2 mg of ²⁴³Am and 1 mg of ²³⁵U. The fission width is calculated in the region where the TOF resolution is sufficient to resolve most resonances at the energy up to 200 eV for ²³⁴U and below 50 eV for ²³⁷Np. The cross-sections in the energy region from 1 to 1000 eV are shown. The new upper limit for the thermal neutron induced fission of ²³⁴U is reported

[en] In this work, the energy shift of X-ray photons at two-photon transition, depending on conversion (either at transition between the second and first excited states or at transition from the first to the ground level), is studied. It is possible to very precisely determine the energy shift of an X-ray photon (on the order of 1 eV) by registering the X-ray photon in coincidence with an X-ray photon of another transition with high resolution detectors; this allows one to determine the change of the mean square radius of the nucleus in the excited state.

[en] The article is devoted to the first attempt to use neutron activation analysis (NAA) to determine the chemical composition of the clay component of the molding mass of archaeological ceramics to identify marker elements characteristic of various medieval ceramic production centers. Fifteen fragments of medieval vessels from the city of Bolgar, the capital of Volga Bulgaria (now the territory of Tatarstan), were provided for research by the Institute of Archaeology of RAS. NAA was carried out by the NAA group of the IREN research facility at the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research. Research has shown that all the studied ceramic samples had no significant differences either in the main components or in the traces. Also results were obtained, previously unknown to researchers of medieval ceramics.

[en] Investigation of the ²³⁵U(n_th, f) reaction using the miniFOBOS double-arm time-of-flight spectrometer of fission fragments confirmed manifestations of the earlier unknown many-body, at least ternary, decay involving almost collinear decay-product escape, which were first observed in the spontaneous fission of ²⁵²Cf(sf). The use of variables sensitive to the nuclear charge of fission fragments allowed the reliability of identification of decay events to be increased and new decay modes to be revealed.

[en] A prototype of a neutron spectrometer based on a gas proportional counter with recoil-proton registration is created at the Frank Laboratory of Neutron Physics at the Joint Institute for Nuclear Research (FLNP JINR) in Dubna. The spectrometer is developed to measure the kinetic energy of protons scattered elastically at small angles that are produced by (n, p) reaction in an environment containing hydrogen. The elaborated prototype consists of two cylindrical proportional counters used as cathodes. They are placed in a gas environment with a common centrally situated anode wire. Studies on the characteristics of the neutron spectrometer were conducted using ²⁵²Cf and ²³⁹Pu-Be radioisotope neutron sources. Measurements were made with monoenergetic neutrons produced by the ⁷Li(p, n)⁷Be reaction when a thin lithium target was bombarded with a proton beam from an EG-5 electrostatic accelerator, as well as with neutrons from the reaction D(d, n) ³He with a gas deuterium target.

[en] At JINR FLNP, on the basis of linear electron accelerator with an energy of up to 50 MeV, the IREN facility was created for research in the field of neutron physics. To perform various tasks, it is necessary to measure the neutron flux density in a wide range of energies - from thermal to fast. This problem is solved by the method of neutron activation analysis by means of gamma spectroscopy of high resolution. For a more accurate determination of the flux of resonance neutrons, it is necessary to calculate the effective resonance integrals in terms of the features of a real spectrum of neutrons and to take into account the thermal motion and absorption of neutrons in the sample. For this purpose, the program for computation of effective resonance integrals was created. Using this program, effective resonance integrals for ¹⁹⁷Au, ⁹⁴Zr, ⁹⁶Zr, ⁶³Cu were calculated, which are significantly different from the values given in the reference book. These results were applied for a more exact determination of flux density of neutrons.

[en] Forthcoming experiments aimed at studying the mechanism of collinear cluster tripartition are planning to be performed with the new facility. Charged products will be registered with the double arm time-of-flight spectrometer composed of mosaics of PIN -diodes and MCP (micro channel plates) based timing detectors. Several tens of ³He-filled counters will be gathered round the ²⁵²Cf source. In order to choose an optimal configuration of the neutron detector and other parameters of the experiment special modeling has performed using both 'neutron barrel' and known MCNP code. The first test run of the new facility is in progress also its 'neutron skin' in under construction.

[en] The cross sections for the excitation of long-lived isomers of ^107,109Ag nuclei are measured in the inelastic scattering of fast neutrons from the IBR-2 reactor of JINR (Dubna). The measurements are performed by means of comparison with the yield of the ^103mRh isomer, for which the excitation cross sections are known over a wide energy range for similar reactions induced by monochromatic neutrons. The measured cross sections proved to be σ(^107mAg)=204±18 mb and σ(^109mAg)=262±26 mb. These values are significantly smaller than the cross section for the excitation of the ^103mRh isomer. An analysis employing information about the arrangement of energy levels in Rh and Ag and about transitions between these levels, as well as data on the spectra of γ rays emitted in (n,n'γ) reactions, reveals that the distinction between the cross sections for the excitation of Rh and Ag isomers can be explained by the difference in the population of corresponding levels of Rh and Ag nuclei

[en] New experimental results on ratio R_dp of the quasielastic charge-exchange yield at the outgoing proton angle θ_p,lab = 0 deg. for the nd ^→ p(nn) reaction to the elastic np ^→ pn charge-exchange yield, are presented. The measurements were carried out at the Nuclotron of the Veksler and Baldin Laboratory of High Energies of the JINR (Dubna) at the neutron-beam kinetic energies of 0.55, 0.8, 1.0, 1.2, 1.4, 1.8, and 2.0 GeV. The intense neutron beam with small momentum spread was produced by breakup of deuterons which were accelerated and extracted to the experimental hall. In both reactions mentioned above the outgoing protons with the momenta p_p approximately equal to the neutron-beam momentum p_n,beam were detected in the directions close to the direction of incident neutrons, i.e., in the vicinity of the scattering angle θ_p,lab = 0 deg. Measured in the same data-taking runs, the angular distributions of the charge-exchange-reaction products were corrected for the well-known instrumental effects and averaged in the vicinity of the incident-neutron-beam direction. These corrected angular distributions for every of nd ^→ p(nn) and np ^→ pn charge-exchange processes were proportional to the differential cross sections of the corresponding reactions. The data were accumulated by Delta-Sigma setup magnetic spectrometer with two sets of multiwire proportional chambers located upstream and downstream of the momentum analyzing magnet. Inelastic processes were considerably reduced by the additional detectors surrounding the hydrogen and deuterium targets. The time-of-flight system was applied to identify the detected particles. The accumulated data treatment and analysis, as well as possible sources of the systematic errors are discussed.