Monitoring of <Superscript>235</Superscript>U content of fuel assemblies for nuclear reactors based on neutron and γ-ray scintillation detector systems

A model of the setup for determining the ²³⁵U content of a fuel assembly for WWER-440 reactors is described. The setup operates based on the digital technology for discriminating neutron and photon scintillation responses. An AmLi source is used as an external neutron source. A three-channel system for detecting fission particle coincidences is based on EJ-309 scintillators. A set of digital codes for obtaining and analyzing neutron-neutron (nn), neutron-γ (nγ), and γ-γ (γγ) coincidences has been developed. Dependences of double coincidences have been experimentally obtained and analyzed with the aim of determining the ²³⁵U content of the fuel assembly. It is shown that fission neutrons and coincidences of the nn and nn + γn + nγ types are the best informative parameters for the ²³⁵U content of the fuel assembly.     

Use of <Superscript>44</Superscript>Ti in the time-differential γγ perturbed-angular- correlation method for studying condensed matter

The principal aspects of ⁴⁴Ti application in time-differential γγ perturbed-angular-correlation method (TDPAC) for studying condensed matter are discussed. In the presented spectrometer modification, the efficiency of ⁴⁴Ti application can be considerably increased by using thin NaI scintillator crystals. Promising techniques for ⁴⁴Ti production and a method for synthesizing samples are described. Examples of TDPAC studies of titanium (rutile TiO₂) and scandium (Sc₂O₃) oxide samples are shown.     

The skipping strategy to reduce the effect of the autocorrelation on the <Emphasis Type="Italic">T</Emphasis><Superscript>2</Superscript> chart’s performance

In this article, we consider the T ² control chart for bivariate samples of size n with observations that are not only cross-correlated but also autocorrelated. The cross-covariance matrix of the sample mean vectors were derived with the assumption that the observations are described by a first-order vector autoregressive model—VAR (1). To counteract the undesired effect of autocorrelation, we build up the samples taking one item from the production line and skipping one, two, or more before selecting the next one. The skipping strategy always improves the chart’s performance, except when only one variable is affected by the assignable cause, and the observations of this variable are not autocorrelated. If only one item is skipped, the average run length (ARL) reduces in more than 30 %, on average. If two items are skipped, this number increases to 40 %.     

Correcting the energy scale nonlinearity of the electromagnetic calorimeter by two-photon decays of a π<Superscript>0</Superscript> meson

A method for correcting the nonlinearity of the electromagnetic calorimeter response is described. This method is based on minimizing the deviation of the measured mass of a neutral π⁰ meson decaying into two photons, depending on their energy. This method has been developed for the LGD2 electromagnetic calorimeter and used in the Hyperon-M experiment at the U-70 accelerator of the Institute for High Energy Physics. The proposed correction technique has made it possible to substantially reduce variations of the reconstructed π⁰ and η meson masses in accordance with their minimum energies.     

A shaper of multiply repeated picosecond high-voltage pulses in a range of 10<Superscript>−10</Superscript> s

A pulse-shaping device is described that reproduces multiply repeated picosecond high-voltage pulses with a duration of 10^?10 s, an amplitude of >100 kV, and a repetition rate of up to 10³ Hz. The principle of switching the circuit using a single spark gap filled with a compressed gas instead of conventional spark peakers and a chopping gap, connected in series, is applied. The use of compressed hydrogen at a pressure of 30 atm as the working gas favors stability of the discharge voltage and a virtually unlimited lifetime of the shaping device.     

A small Raman laser based on a KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> : Nd<Superscript>3+</Superscript> Crystal (λ=1.538 µm) with passive resonator <Emphasis Type="Italic">Q</Emphasis> switching

Generation properties of a Raman laser based on a KGd(WO₄)₂ : Nd³⁺ crystal and operating in a mode of passive resonator Q switching by a YAG : V³⁺ crystal at a wavelength safe for human eyes is studied. A small laser with a mass of 35 g, operating over a wide temperature range at a wavelength of 1.54 µm and an output energy of >6 mJ, has been created on the basis of these studies.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 112–113.Original Russian Text Copyright © 2005 by Ustimenko, Zabotin.     

A photo-thermally stimulated exoemission technique used to study the properties of HTSC ceramics based on YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript>

The method of photo-thermally stimulated exoelectron emission (PTSE) is used to study the processes in the surface layers of HTSC ceramics based on YBa₂Cu₃O_7–. A correlation is observed between variations of the exoemission current and the transition to the superconducting state. The experimentally detected hysteresis in the PTSE intensity of YBa₂Cu₃O_7– ceramics, when thermally cycled in the range T=80–160 K, is limited by two processes. Below T=90 K, the chemisorption has a significant effect on the physical phenomena under study, thus impeding the search for new PTSE regularities in HTSC ceramics. At the same time, exoemission properties of the ceramics considerably change in the range 80–160 K. It is also shown that the superconducting transition and the thermal absorption phenomena for an YBa₂Cu₃O_6.8 specimen are split in the studied temperature range, which allows the PTSE technique to detect the superconducting state and to observe the transition dynamics.Translated from Defektoskopiya, Vol. 40, No. 12, 2004, pp. 54–59.Original Russian Text Copyright © 2004 by Syurdo, Kortov, Milman, Slesarev, Mikhailovich.This revised version was published online in April 2005 with a corrected cover date.     

Dependences of the optical characteristics of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N films on the substrate composition and polarity

Optical properties of Ga- and N-polar triple nitrides Al _x Ga_1−x N with molar fractions of aluminum from 0 to 0.6 are studied by a nondestructive contactless method of spectroscopic ellipsometry. Correlation dependences of the shift of the fundamental absorption edge and the behavior of the real and imaginary parts of the pseudodielectric function on the composition x and polarity of the Al _x Ga_1−x N layers are revealed. It is verified that the polarity of the layers grown by molecular beam epitaxy is defined by the formation of the AlN nucleating layer.     

Environmental Effects on the Tribology and Microstructure of MoS<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–C Films

The tribology of molybdenum disulfide (MoS₂)–Sb₂O₃–C films was tested under a variety of environmental conditions (ambient 50% RH, 10⁻⁷ Torr vacuum, 150 Torr oxygen, and 8 Torr water) and correlated with the composition of the surface composition expressed while sliding. High friction and low friction modes of behavior were detected. The lowest coefficient of friction, 0.06, was achieved under vacuum, while sliding in 8 Torr water and ambient conditions both yielded the highest value of 0.15. Water vapor was determined to be the environmental species responsible for high friction performance. XPS evaluations revealed a preferential expression of MoS₂ at the surface of wear tracks produced under vacuum and an increase in Sb₂O₃ concentration in wear tracks produced in ambient air (50% RH). In addition, wear tracks produced by sliding in vacuum exhibited the lowest surface roughness as compared to those produced in other environments, consistent with the picture of low friction originating from well-ordered MoS₂ layers produced through sliding in vacuum.     

Characteristics of a pulse–periodic CO<Subscript>2</Subscript> laser for applications in the field of laser-produced plasma

The design of a pulse–periodic СО₂ laser oscillator that operates at a high level of the specific energy deposition into a self-sustained discharge is described. The laser is intended for generating pulses with a high-density radiation flux in a laser-plasma generator of multiply charged ions at the Institute of Theoretical and Experimental Physics (ITEP). The results of investigations of the spatiotemporal and energy characteristics of laser output radiation in a wide range of the discharge excitation level and the mixture composition are presented. The optimal conditions are determined under which the oscillator provides an output energy of >10 J in a pulse with a duration of ~28 ns and a record specific peak radiation power of 190 MW per liter of the active volume of a CO₂: N₂: He mixture. The high quality of the spatial characteristics was confirmed in measurements of the radial energy-density distribution in the far-field zone, whose characteristic size is close to the diffraction limit.     

Using the φ-<Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nomogram in calculating the dynamics of a braked wheel

The work deals with the investigation of parameters having effects on road holding and response of wheeled vehicles. A new procedure for evaluating forces in the tire contact area by means of the φ-S _x nomogram accounting for lateral effects on the wheel is put forth. The procedure may be used in assessment of the road holding ability of a vehicle during vehicle design, in selection of a functioning algorithm for the antilock braking systems of vehicles, and also in technical expertise on motor vehicle accidents.     

Effect of Grain Boundary on the Wear Behaviour of NiTi Shape Memory Alloys When <Emphasis Type="Italic">M</Emphasis><Subscript>f</Subscript> &lt; <Emphasis Type="Italic">T</Emphasis> &lt; <Emphasis Type="Italic">A</Emphasis><Subscript>f</Subscript>

Wear behaviour of NiTi SMA is closely corresponds to deformation mechanisms associated with different plastic strain accumulation process. Plastic strain accumulation is achieved by dislocation motion; however, grain boundary acts as a strong barrier. In this work, wear behaviour of single-crystalline and polycrystalline NiTi SMAs was studied to understand the effect of grain boundary on the plastic strain accumulation in the wear process. Wear tests were conducted at M_f < T < A_f, where phase boundary exists between martensitic and austenitic phases. Tests were conducted under ball-on-disc sliding wear mode, and alumina (Al₂O₃) counter-body was used. For single-crystalline NiTi SMA, transition wear occurred even when the applied load was relatively low (i.e., 100 mN). For polycrystalline NiTi SMA, with increasing applied load and wear cycles, the wear has shifted from near-zero wear stage to severe wear stage; no transition behaviour was observed. Significant differences in the wear process were discussed with respect to deformation mechanisms associated with dislocation motion in the single-crystalline and polycrystalline NiTi SMAs.     

Effects of Deposition Conditions and Counter Bodies on the Tribological Properties of Pulsed DC Magnetron Sputtered TiN–MoS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Composite Coating

In the current study, TiN–MoS _x composite coatings were deposited by co-sputtering of MoS₂ and Ti targets under a mixture of Ar and N₂ gas environment using pulsed DC closed-field unbalanced magnetron sputtering. The tribological response of TiN–MoS _x composite coatings was studied against two different counter bodies: cemented carbide (WC–6% Co) ball and pin made of aluminium alloy (AlSiMg). First, the effect of substrate bias was studied on tribological properties using cemented carbide ball. Lowest coefficient of friction in the range of 0.03–0.04 was obtained for the specimen deposited at a substrate bias of −60 V. Wear coefficient was also found to be minimum for the same specimen. Coatings were further deposited at an optimum bias of −60 V in order to vary MoS _x content of TiN–MoS _x composite coating. Effect of variation of chemical composition of the coating was then studied on tribological performance of the coating against aluminium alloy counterface. Excellent anti-sticking property of MoS _x was found to have enabled the TiN–MoS _x composite coating to achieve considerably low coefficient of friction against aluminium alloy. It was shown that with optimum MoS _x content of TiN–MoS _x composite coating, it was possible to attain as low coefficient of friction as 0.09 against aluminium alloy even under normal atmospheric condition.     

Experimental study of effects of water-cement ratio on the acoustic emission rate “<Emphasis Type="Italic">a</Emphasis>” values in concrete

The critical microcracks make durability of the concrete seriously weakened, and the water-cement (w/c) ratio plays a key role in the durability of concrete, acoustic emission (AE) rate “a” value is an effective parameter to evaluate the amount of critical microcracks quantitatively, so the study on the influence factors and the distribution of w/c ratio on the value “a” can provide a promising reference value for the practical engineering. A total of 90 specimens in different w/c ratio are tested under axial compression in the experiment. The whole damage evolution processes are monitored by fulldigital AE acquisition system. The differences of the amount of critical microcracks in different w/c ratio are explored based on the AE rate process theory, and the rule of the effects of w/c ratio on the rate “a” value is revealed through the analysis of fracture energy and cumulative AE energy in the failure process. The results show that a linear relationship was observed between cumulative AE energy and rate “a” value, the amount of critical microcracks and the rate “a” value increase with the increase of w/c ratio, while the cumulative AE energy and cumulative AE hits are on the contrary.     

Microstructure,chemical composition,wear, and corrosion resistance of FeB–Fe<Subscript>2</Subscript>B–Fe<Subscript>3</Subscript>B surface layers produced on Vanadis-6 steel using CO<Subscript>2</Subscript> laser

The paper presents the study results of laser modification of FeB–Fe₂B surface layers produced on Vanadis-6 steel using pack cementation method. Microstructure, x-ray phase analysis, chemical composition study using wave dispersive spectrometry method, microhardness, corrosion resistance as well as surface condition, roughness, and wear resistance were investigated. The diffusion boronizing processes were performed at 900 °C for 5 h in the EKabor® powder mixture. The boronized layers had a dual-phase microstructure composed of two types of iron borides, FeB and Fe₂B, and their microhardness ranged from 1800 to 1400 HV. The laser surface modification was carried out on specimens after diffusion boronizing process using CO₂ laser with a nominal power of 2600 W. Laser beam power used in this experiment was equal to 1040 W and was constant. While the three values of scanning speed were used: 19, 48, and 75 mm/s. During laser modification, the multiple tracks were made where distance between of axis tracks was equal to 0.5 mm. As a result of this process, microstructure consisted of remelted zone, heat-affected zone, and substrate was obtained. In remelted zone, the boron-martensite eutectic was observed. Boronized layers after laser modification were characterized by the mild gradient of microhardness from surface to the substrate and their value was dependent on the scanning speed used and was between 1700 and 1100 HV. Corrosion resistance tests revealed reducing the current of corrosion in case of laser modification process. Wear resistance of laser modified specimens was improved in comparison to diffusion boronized layers.     

A technique for selecting γ rays with energies above 50 GeV from the background of charged particles in the GAMMA-400 space-based γ-ray telescope

The task of selecting neutral γ rays from the background of charged particle fluxes, which arises in investigation of high-energy (>50 GeV) cosmic rays, is complicated by the presence of the backsplash effect. The backsplash is composed of a great number of low-energy (~1 MeV) particles produced in an electromagnetic shower being developed in the calorimeter of the γ-ray telescope. A technique of charged particle rejection using an anticoincidence system has been developed. A method for discriminating events of charged particle detection from γ-ray detection events accompanied by the backsplash phenomenon is proposed. This method is based on the difference of the signals in time and makes it possible to maintain a high detection efficiency even for high-energy γ rays.     

Impact of Wire-EDM on Tribological Characteristics of ZrO<Subscript>2</Subscript>-based Composites in Dry Sliding Contact with WC–Co-Cemented Carbide

In the present investigation, experiments were conducted by unidirectional sliding of pins made of FCC metals (Pb, Al, and Cu) with significantly different hardness values against the steel plates of various surface textures and roughness using an inclined pin-on-plate sliding apparatus in ambient conditions under both the dry and lubricated conditions. For a given material pair, it was observed that transfer layer formation and the coefficient of friction along with its two components, namely adhesion and plowing, are controlled by the surface texture of the harder mating surfaces and are less dependent of surface roughness (R _a) of the harder mating surfaces. The effect of surface texture on the friction was attributed to the variation of the plowing component of friction for different surfaces. It was also observed that the variation of plowing friction as a function of hardness depends on surface textures. More specifically, the plowing friction varies with hardness of the soft materials for a given type of surface texture and it is independent of hardness of soft materials for other type of surface texture. These variations could be attributed to the extent of plane strain conditions taking place at the asperity level during sliding. It was also observed that among the surface roughness parameters, the mean slope of the profile, Δ _a, correlated best with the friction. Furthermore, dimensionless quantifiable roughness parameters were formulated to describe the degree of plowing taking place at the asperity level.     

Indirect measurement of high grid strip densities over Nyquist sampling rate based on the moiré pattern analysis for quality assurance in grid manufacturing

We have recently developed very precise carbon-interspaced antiscatter grids having a wide range of grid strip densities (i.e., 85–234 lines/in.) by adopting the sawing process, depending on the demands of specific imaging modalities. However, because grid strips of the recently developed grids are mostly invisible through X-ray nondestructive testing due to their high strip densities, quality assurance in the manufacturing has not yet satisfactorily made. In this work, we proposed a pragmatic method to measure actual grid strip densities over the Nyquist sampling rate based on the moiré pattern analysis. We prepared several samples of the carbon-interspaced grids having nominal grid strip densities of 85, 103, 130, 150, 178, 203, 215, and 234 lines/in. and measured their strip densities by using the proposed method to demonstrate its viability assessment. The differences between the nominal and the measured grid strip densities were less than about 1.8%, indicating the proposed method is useful for the quality assurance in grid manufacturing.     

Hamon 10 × 100 MΩ resistor based traceable source for calibration of picoammeters in the range 100 pA–100 nA

This paper describes a measurement method developed at National Institute of metrological Research (INRIM) to calibrate picoammeters in dc current from 100 pA to 100 nA. The current source is based on a traceable to the dc resistance national standard 10 × 100 MΩ Hamon resistor developed at INRIM and on a traceable to the dc voltage national standard high precision dc voltage calibrator. The expanded uncertainties of the method for the calibration of picoammeters span from 9.4 × 10⁻⁴ for the gain of a picoammeter at 100 pA to 4.0 × 10⁻⁴ for the gain at 100 nA. A detailed uncertainties budget at 10 nA level and the results of a comparison with a different technique are also reported.