Temporal characteristics of light collection in the liquid scintillation counter with a volume of 1.5 m<Superscript>3</Superscript> and quasi-mirror reflection

The temporal behavior of light collection in the 1.5-m³-volume mirror-reflecting counter filled with a highly transmitting liquid scintillator has been investigated. Using the Monte Carlo method and assuming that the luminescence decay time of the liquid scintillator is zero (τ_LS = 0), it has been ascertained that, in the case of a short flash in a counter, the exponential phase of light collection is characterized by time τ_col = 15.0 ± 1.7 ns, which is does not depend on scattering of light in the medium. The measured exponent index τ_act = 37 ± 3 ns of an actual pulse due to a muon is determined both by light collection time τ_col ≈ 15 ns and luminescence decay time τ_LS ≈ 20 ns of the scintillator in the large-volume counter.     

Spectral-luminescent properties of gradient-activated LiNbO<Subscript>3</Subscript> crystals with concentration profiles of Yb<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> ions

The luminescent properties of gradient-activated crystals of lithium niobate with concentration profiles of optical centers, ytterbium and erbium ions, are studied. It is shown that the spectral-luminescent properties of the gradient crystals are correlated with the concentration profiles of optical centers — donors Yb³⁺ and acceptors Er³⁺.     

Features of the <Superscript>85</Superscript>Rb Spectrum in a Cell with an Antirelaxation Coating

Distortion of the spectrum of the D₁-line of ⁸⁵Rb in optical cells with an antirelaxation coating on the inner walls of the cell is studied. The spectrum shape is found to be significantly dependent on the velocity and direction of changes in the laser frequency. A physical explanation is provided for these features, which are confirmed by numerical simulations. The effect of the magnetic field on the spectrum shape is discussed.     

Energy spectra of neutrons escaping from light and heavy fragments with asymmetric <Superscript>235</Superscript>U and <Superscript>252</Superscript>Cf nuclear fission

The neutron-activation analysis is used to determine the energy spectra of neutrons escaping from light and heavy fragments from nuclear fission of ²³⁵U by thermal neutrons and spontaneous fission of ²⁵²Cf nuclei. It is shown that the difference of the spectra obtained is slight, ∼90.6 keV. The 28-group energy spectra of instantaneous neutrons from fission of ²³⁵U and ²⁵²Cf nuclei, which were reconstructed using four-component a priori spectra, are presented.     

Pulse shape analysis and identification of multipoint events in a large-volume proportional counter in an experimental search for 2<Emphasis Type=Italic>K</Emphasis> capture of <Superscript>78</Superscript>Kr

57-69A pulse shape analysis algorithm and a method for suppressing the noise component of signals from a large copper proportional counter in the experiment aimed at searching for 2K capture of 78Kr are described. These signals correspond to a compound event with different numbers of charge clusters from primary ionization. A technique for separating single-and multipoint events and determining the charge in individual clusters is presented. Using the Daubechies wavelets in multiresolutional signal analysis, it is possible to increase the sensitivity and the resolution in extraction of multipoint events in the detector by a factor of 3–4.     

Determination of the <Superscript>14</Superscript>C Concentration in a Liquid Scintillator for a Neutrino Detector

A setup has been developed for studying ultralow ¹⁴C concentrations in liquid scintillator samples for a large neutrino detector. The setup is located at the low-background underground laboratory of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) at a depth of 4900 m of water equivalent. The ¹⁴C concentrations in a liquid scintillator based on linear alkyl benzene, the background counting rates, and the spectra of particle energies deposited in the technological scintillator sample have been measured. The ratio ¹⁴C/¹²C = (1.41 ± 0.12) × 10^–16 has been obtained. A model of the γ-ray background has been developed, with which it is possible to extract the energy spectrum of 14C and reduce the systematic uncertainty of measurements.     

Plasma erosion opening switch for fast discharges with current growth rate about 10<Superscript>12</Superscript> A/s<Superscript>1</Superscript>

The article presents the construction of a plasma erosion opening switch, capable of creating the discharge with electrical current of several tens kiloamperes and a growth rate up to 10¹² A/s in the circuit with the inductive load up to 100 nH. The results of test experiments with imitator of load are presented. The discharge circuit under consideration will be used for the experiments for creation of shock waves in plasma.     

A high-energy YAG: Nd<Superscript>3+</Superscript> laser with a phase conjugation in an optical fiber

An optical scheme and design of a YAG:Nd³⁺ frequency laser with a two-pass amplifier and a mirror with the phase conjugation by the stimulated Brillouin scattering in an optical fiber is described. The maximal radiation energy is 1000 mJ at a 1.064-μm fundamental wavelength and 500, 200, and 20 mJ at the second, fourth, and fifth harmonics, respectively, when the divergence is ∼5 × 10⁻⁴ rad and the pulse duration is 4.5 ns.     

A high-energy YAG:Nd<Superscript>3+</Superscript> laser with fiber destroyed radiation coherence

The optical scheme and the design of a high-power YAG:Nd³⁺ laser, which generates radiation pulses of nanosecond duration at wavelengths of 1064 nm (0.8 J), 532 nm (160 mJ), and 266 nm (40 mJ) with destroyed coherence in a fiber and a smoothed intensity distribution in the beam cross section, are described. The processes that affect the generation efficiency of decoherenized radiation are considered.     

Calibrating the forward calorimeter of the CMS detector using a <Superscript>60</Superscript>Co radioactive source

Three methods for calibrating the forward calorimeter (HF) of the CMS detector using a ⁶⁰Co radioactive source with an activity of 5 mCi are discussed. These methods are shown to provide a calibration accuracy of ～5% with respect to the calibration on a 100-GeV electron beam.     

Studying the dependence of the ratio of the prompt neutron yields in the symmetric and asymmetric fission of <Superscript>235</Superscript>U and <Superscript>238</Superscript>U nuclei on the energy of neutrons inducing this fission

The ratios have been measured of the prompt neutron yields in the symmetric and asymmetric fission of ²³⁵U nuclei induced by thermal neutrons and fast neutrons of pulsed nuclear reactors, as well as in the ²³⁸U fission induced by 14.7-MeV neutrons. The well-known measured integrated cross sections of the system of dosimetric nuclear reactions are compared to the cross sections calculated using the differential cross sections from the data libraries known worldwide, the three-component representation of fission neutron spectra from ²³⁵U and ²⁵²Cf nuclei, and the KASKAD spectrum reconstruction program.     

Production of <Superscript>10</Superscript>Be isotope from boron carbide irradiated with fast neutrons

A method for producing ¹⁰Be isotope from spent rods of the emergency protection and compensation systems of a fast neutron reactor is described. This isotope has found application in targets and radioactive beams for experiments at modern heavy-ion accelerators. The mass of ¹⁰Be obtained using this technique is 2.7 mg, which is five times the mass of this isotope produced throughout the world to date. A method for determining the ¹⁰Be concentration in the source material and intermediate fractions of its processing has been developed. This method is based on analysis of γ and β spectra of samples, measured by HPGe and Si(Li) detectors. A prototype of the ¹⁰Be oxide target has been manufactured. The parameters of the target prototype have been determined, and its vacuum testing has been performed.     

Investigating the 1/<Emphasis Type="Italic">z</Emphasis><Superscript>2</Superscript>-filtering in tomography algorithms

The filtering of projections in tomography algorithms, which is based on the regularization of distribution 1/z ², is investigated. Numerical simulations validate that changing the filter support will substantially improve the tomograms. Comparison of the results of reconstruction by the 1/z ²-filtering algorithm and the Shepp-Logan algorithm shows that the reconstruction accuracy of the latter is worse when the number of angles of observation is small or a high noise is present in the projection data.     

An indirectly heated metal oxide hot cathode with a 100-cm<Superscript>2</Superscript> area

Results of designing of a sectioned metal oxide hot cathode with indirect heating and a total emission coating area of 100 cm² are described. The design of the hot cathode enables control of the working surface temperature and allows one to change emission surface without replacing the whole hot cathode. The thermal test results are presented. The possibility is shown of applying the hot cathode in the uncharacteristic mode of gas discharge formation in medium vacuum conditions.     

Studying kinetics of scintillation process in a CaMoO<Subscript>4</Subscript> crystal

The kinetics of scintillation process in Czochralski-grown CaMoO₄ crystals excited by α particles and γ rays from ²³⁸Pu and ¹³⁷Cs radioactive isotopes, respectively, is investigated. Kinetics of scintillations is shown to be complex and multicomponent in character. Fast and slow scintillation components are observed, and their relative contributions to the total light yield in the scintillator are determined. The possibility is demonstrated of discriminating between scintillator signals due to α particles and γ rays.     

Study of Neutron Spectra Near the Surfaces of Iron and Water Spheres with <Superscript>252</Superscript>Cf Sources at Their Centers

The neutron-energy spectra at a distance of 30 mm from the surfaces of metal and water spheres that contain a ²⁵²Cf neutron source at their centers were measured and calculated. Measurements were performed using hydrogen counters and activation and fission detectors.     

A Fluorimeter on the Basis of a Femtosecond Cr<Superscript>+4</Superscript>: Forsterite Laser

An apparatus for measuring luminescence lifetimes using the femtosecond up-conversion method is presented. A laser system based on a chromium–forsterite crystal with a lasing wavelength of 1250 nm is used to generate ultrashort pulses. Luminescence is excited in a sample by optical harmonics that are generated in nonlinear optical crystals. The width of the instrument function of the system is 200 fs. Methods for optimizing the signal-to-noise ratio in measurements are discussed. The results of measurements of the fluorescence- decay dynamics and the anisotropy of aqueous solutions of an inclusion complex of the 4-DASPI styrene dye in cucurbit[6]uril on short (5 ps) and long (500 ps) time scales are presented.     

Monte Carlo simulation of the formation of A<Superscript>III</Superscript>B<Superscript>V</Superscript> nanostructures with the use of droplet epitaxy

A Monte Carlo lattice model is proposed to describe the formation of semiconductor nanostructures by the vapor–liquid–solid growth mechanism. This model is used to simulate the growth of GaAs nanostructures by the droplet epitaxy technique in the temperature range from 500 to 600 K in As₂ fluxes with intensity of 0.005–0.04 ML/s. The morphology of the formed structures is demonstrated to depend on the growth parameters. Etching of the GaAs substrate by a gallium droplet is studied. The ranges of temperature and As flux rates necessary for the formation of GaAs nanorings are determined. The conditions of the formation of single and double concentric rings are analyzed.     

Experimental Study of the Deformation of Instantaneous Neutron Spectra from the Fission of <Superscript>235</Superscript>U Nuclei in Fast-Reactor Core Materials

The results from studies of the deformation of the instantaneous neutron spectra resulting from the fission of ²³⁵U nuclei in the material of structural elements of a fast reactor core are presented. The neutron spectra at and near the center of the reactor core were measured using neutron activation and fission neutron detectors.__________Translated from Pribory i Tekhnika Eksperimenta, No. 4, 2005, pp. 15–25.Original Russian Text Copyright © 2005 by Sevast’yanov, Koshelev, Maslov.     

Asymmetric fission of <Superscript>235</Superscript>U nuclei induced by thermal neutrons and fast neutrons of pulsed nuclear reactors

The contributions that neutrons emitted from the neck of excited dumbbell-shaped fissioning ²³⁵U nuclei at the instant of their fission make to the prompt fission neutron spectrum, as well as the ratios of these contributions, have been measured for nuclear fission induced by thermal neutrons and fast neutrons of pulsed nuclear reactors.