7 Be (T 1/2 = 54 days, E γ = 478 keV) is formed in the upper layers of the atmosphere in reactions where cosmic rays split nitrogen and oxygen atoms. The 7 Be ions formed attach to dust and aerosol particles and fall together with them onto the Earth's surface [1]. We present below the results of γ-spectrometric studies of the activity of 7 Be (N) in monthly (m) atmospheric fallout in the period 2004-2005 in Samarkand and compare these data with the amount of precipitation, average humidity, and average air temperature (data from the Samarkand regional hydrometeorological office).The atmospheric fallout samples were obtained as follows. A 100 × 100 cm and 10 cm high Duralumin vessel, whose bottom was smeared with 100 g of glycerin and covered with a layer of gauze, was exposed monthly on the roof of an 8 m high building. After the exposure was completed, the gauze we removed from the vessel. Any rain water or snow present in the vessel was evaporated to volume ≤100 ml, and the vessel was carefully wiped clean with fresh gauze.Two types of samples were prepared successively from the atmospheric fallout:• the gauze was allowed to dry (samples G with mass 180-230 g) and then folded into strips and neatly packed into one-liter Marinelli vessels; • after the samples G were measured, the gauze was removed from the Marinelli vessels, placed in a porcelain cup, and calcined in a muffle furnace (≤400 °C); the ash was packed into a 40 × 40 mm polyethylene packet (samples A with mass ∼8-25 g). Inert samples, prepared by the methods indicated above from 1 m 2 clean (unexposed) gauze, were used to determine the background component in the spectra of the experimental samples.The γ-ray spectra of the samples were measured with a 63 × 63 mm NaI(Tl) scintillation crystal and a 100 cm 3 Ge(Li) detector with resolution ∆E γ /E γ ≈ 10% and ∆E γ = 6.7 keV, respectively, on the 1332 keV 60 Co line, which were placed inside lead shielding with 10 cm thick walls. The MARS (JINR, Dubna) computer program was used for acquisition and processing of the spectra. The duration of individual measurements was 2-6 h.The γ-ray spectrometers were calibrated with respect to detection efficiency using 226 Ra, 232 Th, 40 K, and 137 Cs from the OMASN system (for the G samples) and 241 Am, 22 Na, and 137 Cs from the OSGI system (for the A samples).A dominant contribution from the background radiation to the intensity was observed, together with contributions from 7 Be and 226 Ra, 232 Th, and 40 K of natural origin, in the instrumental spectra of the samples. In the semiconductor spectra of the samples which were (Fig. 1) and were not (Fig. 2) calcined, the 478 keV 7 Be total absorption peak is well resolved

7 Be (T 1/2 = 54 days, E γ = 478 keV, a γ = 10.3% per decay) is produced in the upper layers of the Earth's atmosphere in reactions where cosmic rays split 16 O and 14 N nuclei. In addition,7 Be nuclei formed as a result of the fragmentation of heavy nuclei and in thermonuclear fusion reactions 3 He + 4 He = 7 Be + γ on the surface of the Sun and in other parts of the Universe penetrate into enter the Earth's atmosphere. 7 Be ions stick to aerosols and are transported together with them into the lower layers of the atmosphere whence they fall with wet (rain, sleet, snow) and dry (dust, dew) precipitation onto the Earth' surface. Studies performed over many years in different regions of the Earth have established that the 7 Be concentration in the air layer at the ground is correlated with solar activity and the local physical-geographic characteristics while for atmospheric precipitation there is a correlation with the amount of the wet precipitation [1][2][3][4]. Systematic studies of monthly atmospheric precipitation of 7 Be in Samarkand began in 2002 [5][6][7].The present work compares the regularities observed in variations of 7 Be activity in atmospheric precipitation in 2002-2005 in Samarkand with those found in other regions of the Earth.Methodology. Atmospheric precipitation (dry and wet) was sampled by the "sticky table" method: monthly exposure of a container (area 100 × 100 cm, depth 10 cm) whose inner surface was smeared with glycerin and screened with gauze. After exposure was completed, the gauze was removed from the container and the liquid was poured into a vessel and evaporated to dry residue. The container and vessel were carefully rubbed with clean gauze, and the exposed and rubbing gauze with mass 180-250 g were placed into one-liter Marinelli vessels or incinerated in a muffle furnace and packed into 40 × 40 mm (8-25 g) polyethylene packages.The γ-spectra of the samples were measured in a gamma-spectrometer with a Ge(Li) detector with volume V = 100 cm 3 and energy resolution ΔE γ = 6.2 keV at E γ = 1332 keV or with a scintillation detector with a 63 × 63 mm Na(Tl) crystal with detection efficiency ΔE γ /E γ~ 10% on the 1332 keV line.The semiconductor spectra were processed with a computer program developed at the Mendeleev All-Russia Research Institute of Metrology. It was found that the detection efficiency of the Ge(Li) detector entered into the code is overstated. As a result, the 7 Be activity presented in [5, 6] in 2002-2003 for the samples is understated by a factor of 2.25 (the corrected values are given in Table 1).The scintillation spectra were processed by decomposing them into background components -radionuclides of the uranium-thorium families, 40 K, and 7 Be [8].Correlation of 7 Be Content in Atmospheric Precipitation with Precipitation Amount, Solar Activity, and Air Temperature. In Samarkand, there is a nonlinear correlation between 7 Be activity A in atmospheric precipitation and the precipitation amount H, solar activity W, and air temperature T.

The neutron flux density from 0.025 eV to 12 MeV has been measured experimentally in all channels of the VVR-SM core by the activation method using threshold monitors (Au, Ni, Fe. Ti, Mg, Y). Comparing with a calculation of the neutron flux density at different energy using the IRT-2D computer code showed agreement to within 5%. The distribution of the neutron fluxes and spectra in the core, which is of practical utility for radiation technologies, was obtained. A series of irradiations has been conducted and experimental dependences of the irradiation time on the channel position in the core as well as on the size of the stones for obtaining a standard light blue and dark blue color have been obtained. The irradiation conditions making it possible to lower the induced radioactivity of the minerals three-fold as a result of increasing the ratio of the fast to thermal neutron fluxes are found.The main parameters characterizing research reactors are the neutron flux density in the core and the neutron energy spectrum. The flux density of the main neutron energy groups in the experimental channels of water moderated and cooled reactors is of great interest for practical applications of activation analysis, radiation technology, as well as testing of different materials and semiconductor devices for radiation resistance of their functional characteristics. In this connection, the prime problem is finding the distribution of the neutron flux and spectrum over the channels inside the core of the reactor; the difficulty is that it is impossible to detect neutrons directly and determine their energy.It is known that the thermal neutron flux density can be determined from the (n, γ) reaction products, which are formed when a monitor is irradiated, as the difference of the indications of a counter without and with a filter. Threshold reactions are used to recover the fast-neutron spectrum. Since the differential measurements of a neutron spectrum are difficult to perform, and there is no need for them in analytical measurements, ordinarily the integral fluxes of neutrons above some threshold value are evaluated.The structural features of some irradiation channels in research reactors make it impossible to determine the neutron flux experimentally and to reconstruct the neutron energy spectrum. In such cases, these parameters are determined by, for example, solving a system of differential equations governing diffusion [1]. Several types of applied programs are available for calculating the neutron flux density. A program for calculating the neutron flux density in three-dimensional space by the Monte Carlo method has been developed at the Los Alamos National Laboratory (USA) [2]. This program is considered to be universal and is the only program that takes account of published data on neutron-physical interaction constants for neutrons interacting with different atoms at different energies as well as the energy spectrum of neutrons formed as a result of the fission of 235 U nuclei in fuel. In addition, it permits setting t...

fuel assemblies with high-enrichment uranium, which are removed at the end of each cycle, will be replaced with IRT-4M fuel assemblies with low-enrichment uranium. This will require increasing the core size up to 20 fuel assemblies and increasing the power of the reactor to 11 MW. The methods used for and the results of neutron-physical calculations (burnup, power distribution, subcriticality), thermohydraulic analysis, and calculations of the kinetic parameters of a stable state are described for a core with high-enrichment uranium, a mixed core, and the first full core with low-enrichment uranium.