In the present work we found the maximum discovery distance for 239Pu-Be source using the detectors based on ZWO (ZnWO4) and BGO (Bi4Ge3O12) oxide scintillators. Detection distance was defined by using the radiation monitoring system ”PORTAL”. This research gives us data for estimation of the contribution of low-energy cascade gamma quanta CGQ. The CGQ emitted by excited scintillator nuclei defined the effective discovery distance of the fast neutrons source. The maximum detection distance was obtained with PMT in a single-photon counting mode. The maximum discovery distance for a BGO scintillator of size Ø40×40 mm – 38 cm, ZWO scintillator of size Ø52×40 mm – 54 cm, with reliability about 0.001. The results of the experiment on the ZWO scintillator can be explained by the registration of additional gamma quanta from the inelastic scattering reaction and the CGQ arising from resonant neutron capture region. This two mechanisms further lead to increase the sensitivity of the detector and increase the detection distance of the monitoring system. The key features of the monitoring system are: ZWO oxide scintillator, wide band measuring path, utilize PMT in single photon mode. The obtained detection distance was about 1.4 times higher in comparison with the spectrometric recording mode and 1.9 times higher in values of efficiency. Our results demonstrate the advantages of the ZWO scintillator compared to the BGO and demonstrate the possibility of using the resonant capture mechanism by ZWO detector nuclei to increase the fast neutrons sensitivity. The resonance capture mechanism increase sensitivity and maximum detection distance of the monitoring system. The low-energy gamma-quanta, which discharge of compound nuclei, are substantially suppressed in comparison with the classic spectrometric recording mode.

When a fast charged particle passes through matter, it loses some of its energy to the excitation and ionization of atoms. This energy loss is called ionization energy loss. In rather thin layers of matter, the value of such energy loss is stochastic. It is distributed in accordance with the law, which was first received by L.D. Landau. In amorphous substances, such a distribution (or spectrum), known as the Landau distribution, has a single maximum that corresponds to the most probable value of particle energy loss. When a particle moves in crystal in a planar channeling mode, the probability of close collisions of the particle with atoms decreases (for a positive particle charge) or increases (for a negative charge), which leads to a change in the most probable energy loss compared to an amorphous target. It has recently been shown that during planar channeling of negatively charged particles in a crystal, the distribution of ionization energy loss of the particles is much wider than in the amorphous target. In this case, this distribution can be two-humped, if we neglect the incoherent scattering of charged particles on the thermal oscillations of the crystal atoms and the electronic subsystem of the crystal. This paper explains the reason for this distribution of ionization energy loss of particles. The ionization energy loss distribution of high-energy negatively charged particles which move in the planar channeling mode in a silicon crystal are studied with the use of numerical simulation. The dependence of this distribution on the impact parameter of the particles with respect to atomic planes is considered. The dependence of the most probable ionization energy loss of particles on the impact parameter is found. It is shown that, for a large group of particles, the most probable ionization energy loss during planar channeling in a crystal is lower than in an amorphous target.

By calculation methods, the dose rate of the radioactive waste, behind concrete protection, was evaluated in current work. Parameters, which were taken in account in the calculations, are geometry of the protection shell, size of the source and its isotopic composition. As model geometrical parameters the spent fuel assembly's size and thickness of the concrete wall of the ventilated storage container (VSC)-VVER were taken. The computer program that does numerical calculation was composed in the Wolfram Alpha environment. The program takes into account change of the isotopic composition and spectra of gamma-radiation with time. Calculation results were compared to the known data on the spent nuclear fuel heat dissipation. Approach described in this work can be used for fast estimation of change in the quality of radioactive waste (RAW) in the long-term storage without recycling, for different initial isotopic composition. Obtained results were analyzed on the matter of change in gamma-radiation of RAW. В данной работе численными методами рассчитывалась мощность дозы излучения радиоактивных отходов за бетонной защитой. При расчётах учитывались геометрия защитной оболочки, размер источника и его изотопный состав. В качестве модельных геометрических параметров были взяты размеры отработанной тепловыделяющей сборки (ОТВС) и толщина стенки бетонного вентилируемого контейнера хранения (ВКХ)-ВВЭР. Для проведения численных расчётов, в среде Wolfram Alpha была составлена программа. В программе учитывается изменение изотопного состава отработанного ядерного топлива со временем и изменение энергетического спектра гамма-излучения. Проведено сравнение результатов вычисления с известными данными по тепловыделению отработанного ядерного топлива (ОЯТ). Используемая методика позволяет проводить быструю оценку изменения качества радиоактивных отходов (РАО) при долговременном хранении без переработки, для различных изотопных составов топлива. По результатам расчётов был проведён анализ изменения гамма-излучения РАО. КЛЮЧЕВЫЕ СЛОВА: радиоактивные отходы, мощность дозы, долгосрочное хранение, бетонная защита, изотопный состав KEYWORDSProduction and accumulation of the radioactive waste (RAW) are one of the major problems associated with the use of nuclear energy in any of its forms. According to the existing data, there is about 300 thousand tons of accumulated spent nuclear fuel (SNF) with total activity of ~10 20 Bk, and by year 2030, this quantity is predicted to be 500 thousand tons. In particular, importance of this problem is reflected by the fact, that in the last years several monographs [1][2][3][4][5] on the problems of dealing with RAW were published.Leaving aside the cosmic origin and associated with uranium mining radionuclides, in this paper we will consider 2 forms of RAW: 1) contained in SNF; 2) the so-called operational waste of nuclear plant. According to the established terminology, in countries, where radiochemical or other recycling is not intended (for example -Ukraine), it belongs to the high-level RAW (HLW).

The sample preparation method and the results of experimental measurements of the concentration of beta-radioactive aerosols (the decay products of Radon-222 in the air) are presented. The experimental equipment includes an electrostatic aerosol collector and a time spectrometer based on the PMT with a plastic scintillator and Wilkinson’s ADC. The accumulation of aerosols on the foil lasted for about 12 hours. The activity of accumulated aerosols was measured in the time interval of 0 to 300 minutes. The use of the spectrometer in the time analyzer mode, the proposed aerosol accumulator, and the method of processing the accumulated spectrum makes it possible to increase the sensitivity of the radiometer in comparison with the collection method based on air filters. Applying the time‑spectrum development procedure to the constituent components makes it possible to reliably establish the connection of aerosols registered in the room with β‑active decay products of radon-222: Po-218, Pb-214, Bi-214.