Studying the Stability of Nanosecond Light-Pulse Sources Based on Blue GaN and InGaN Light-Emitting Diodes

The results of studying the stability of the parameters of nanosecond light-pulse sources based on bright blue light-emitting diodes are presented. These diodes were developed by the Nichia and Kingbright companies for calibration measurements in the HT-200 deep-water neutrino telescope, the MAGIC atmospheric Cherenkov telescope of high-energy quanta, and the wide-aperture Cherenkov detector of extensive air showers. The time stability of light sources is no worse than 1%. The changes in their light yields within a temperature range of –3 to +45°C are +7 and –9%, respectively.     

A Low-Noise Fast Eight-Channel Preamplifier

A preamplifier with a rise and fall time of 2.5 ns is described. At the output of a transmitting 50- cable with matched terminations at both ends, and the input-equivalent circuit noise is 20 V at an amplification factor of 7.5. Eight such preamplifiers are placed inside a unit with dimensions of 8 × 16 × 4 cm.     

Interferometric Methods for Surface Testing. High-Order White-Light Interferometer

A high-order white-light interferometer for three-dimensional fast noncontact testing of optical surface profiles is described. The device ensures measurements of absolute flatness deviations to an accuracy of /1000 within a wide technological field of 80 mm (the resolution in the plane is 0.1 mm).     

An Optical-Fiber Setup for Inert Particle Concentration Measurements

An optical-fiber setup employing laser light designed to measure concentrations of 50-to 500-m particles moving with a speed of up to 10 m/s is described. The time resolution, the measurement time, and the counting of pulses reflected from the particles are programmed. The setup has the following basic parameters: time resolution is 10 s, spatial resolution is 50 m, sample size is up to 32 × 10³, and particle counting error is within 1%. The setup was applied to measurement of the solid-phase concentration in a two-phase flow in a volum concentration range of up to 30%.     

Investigation of the Internal Amplification Effect on Planar (p +–n–n +) Structures Made of High-Resistivity Silicon

The first results of studies of special strip and pixel silicon detectors are presented. The detector structures allow the creation of high electrical fields (5 × 10⁵ V/cm) near p–n junctions that are powerful enough to initiate an avalanche multiplication of charge carriers. The possibility of internal amplification in a semiconductor detector similar to the proportional amplification in gas counters is shown. The spectrum of particles from ²³⁸Pu (E = 5.5 MeV) demonstrates an amplified peak at an energy of 70.2 MeV and an energy resolution FWHM = 10.2 MeV.     

An integral method for measuring the <Emphasis Type="Italic">P</Emphasis>-odd asymmetry on a reactor at neutron polarization switching frequencies higher than the frequencies of the main spectrum of the neutron noise power

P-odd asymmetry is measured when frequencies of switching neutron polarization exceed the frequencies of the reactor power fluctuations that govern the spectral density of noise power. A principle for recording the current signals in these measurements is described. This method was used for the first time at the Konstantinov Institute of Nuclear Physics in Gatchina (Russia). The results suggest that the accuracy of measurements at an increased equipment-switching frequency is even higher than the accuracy obtained using compensation for reactor power fluctuations; hence, this compensation becomes superfluous. Following this method, it is possible to take measurements with a single detector and to dispense with a monitor, thereby rendering the equipment and the measuring technique less complex. A strategy of measurements was developed. An experimental model of the facility was produced and tested with a small-amplitude calibration signal in the presence of reactor power fluctuations caused by rays from reaction ¹⁰B(n )⁷ Li* ⁷Li + . The results from the test measurements of the P-odd effect in reaction ³⁵Cl(n, )³⁶Cl are presented.Translated from Pribory i Tekhnika Eksperimenta, No. 1, 2005, pp. 62–71.Original Russian Text Copyright ¢ 2004 by Vesna, Shulgina.     

An Energy Source Based on Helical Explosion–Magnetic Generators for High-Impedance Loads

A transportable standard module developed at the Institute of Experimental Physics as a component of an energy source for modeling current pulses of positive lightning is described. The source is designed as a combination of several unified helical explosion–magnetic generators with output transformers and an inner diameter of the stator of 200 mm. According to our calculations, the source generates current pulses with an amplitude of up to 100 kA in loads with an inductance of 100 H and a resistance of several tens of ohms. The results from testing a typical module operating with a circuit having an inductance of 100 H and a resistance of 4 are presented. The experimental data coincide well with the results of a mathematical simulation of the module's operation.     

A Coordinate Detector for Studying Horizontal Fluxes of Cosmic Rays

A DECOR coordinate detector is a multilayer system of plastic streamer tube chambers located around a NEVOD Cerenkov water calorimeter. The basic characteristics of the detector are as follows: the area is 100 m², the angular resolution is 1°, and the space resolution is 1 cm. The structure of the detector, data acquisition and trigger systems, and results obtained during the operation of a pilot assembly (8 chamber layers and a working area of 8.4 m²) are given.     

The Tribological Properties of Monolayer KCl Films on Iron in Ultrahigh Vacuum: Modeling the Extreme-Pressure Lubricating Interface

The friction coefficients of thin KCl films deposited onto clean iron in ultrahigh vacuum are measured using a tungsten carbide tip. A rapid decrease is found in the friction coefficient from 2 for clean iron to 0.27 ± 0.03 after the deposition of 40 Å of KCl. Based on previous contact resistance measurements, this was proposed to be due to the completion of the first layer of KCl. The first-layer KCl coverage was measured by adsorbing deuterium onto an iron surface partially covered by KCl, where deuterium selectively adsorbs onto the iron. This revealed that the first monolayer is complete after the deposition of 40 Å of KCl and that the first-layer KCl film coverage _KCl ⁽¹⁾ is given by _KCl ⁽¹⁾ = 1 - exp(-0.39±0.02t), where t is the film thickness. XPS data suggest that heating a KCl film to 550 K causes it to wet the surface. This leads to decreases in the friction coefficients for thin KCl films in accord with the idea that friction is reduced by the first monolayer of KCl on iron. Temperature-programmed desorption data indicate that KCl in the first monolayer is 5 kJ/mol more stable than the multilayer consistent with the wetting behavior. Finally, the kinetic data are analyzed to suggest that the first-layer film is 2.6 Å thick.     

Formation of High-Power Pulses of Nanosecond Duration by Generators on Reverse Switch-on Dynistors with Sharpening Circuits Based on Diode Opening Switches

The basic principles of constructing generators of nanosecond pulses on reverse switch-on dynistors with sharpening output circuits based on diode opening switches are considered. The results of an experimental study of a high-power generator incorporating such a dynistor; a step-up pulse transformer; and a high-voltage diode opening switch, which is an assembly of drift step-recovery diodes connected in series, are presented. The output voltage pulses of the generator with an amplitude of 45 kV, a duration of 50 ns, a rise time of 10 ns, and a repetition rate of 1 kHz are applied to a load resistance of 25 .     

A Helical Magnetic-Cumulation Generator with a Compact Transformer

Experimental data on a helical magnetic-cumulation generator with an output step-up transformer formed by two coaxial solenoids is presented. The inner diameter of the helix is 50 mm. Compared with the transformers described earlier, this transformer has a smaller size. The transformer can feed an energy of 1 kJ into a 100-H high-impedance load.     

Time-of-Flight Characteristics of Scintillation Counters with Fine-Mesh Photomultipliers

The characteristics of the time-of-flight system of scintillation counters with the -527 and R5505 fine-mesh-dynode photomultipliers for high-magnetic-field environment were measured. Scintillation counters with thin plastic scintillators 1, 3, and 5 mm thick were designed to operate in comparatively strong stray magnetic fields of up to several kilogauss. The measurements were carried out in beams of the U-10 proton synchrotron (Institute of Theoretical and Experimental Physics) with proton, ⁺-meson, and ^–-meson momenta of 0.63, 1.03, and 1.28 GeV/c. For counters with scintillator sizes of 1 × 20 × 154 mm (BI-408) and 3 × 20 × 200 and 5 × 20 × 200 mm (Kuraray and SCSN-81), time resolutions of 45–180 ps were obtained. The time resolution of the scintillation counters, in which scintillators 20 mm thick and -527 photomultipliers were used, was found to be 50–80 ps.     

A Unit for Microwave Investigations of High-Temperature Superconductivity in a Magnetic Field

A simple updating of an P 1306 spectrometer for microwave absorption measurements in a low-induction magnetic field at temperatures of down to 15 K is described.     

Formation of lubricant “moguls” at the head/disk interface

In a typical head/disk interface of a rigid disk drive, the motion and redistribution of a 14 Å thick lubricant film on the disk under a flying slider is analyzed with an optical surface analyzer. At short times (seconds to a few minutes), the film is rearranged in an isotropic manner, creating a pattern of moguls¹ of 100 m in lateral size and a few angstroms in height. A strong correlation is demonstrated between the resulting distribution of the lubricant film and the underlying substrate topography. Surprisingly, lubricant becomes thicker on the peaks of the micro-waviness, and thinner in the valleys. Possible mechanisms for this unexpected behavior will be discussed, as well as its tribological implications. At longer times, the lubricant film is pushed away from underneath the slider, creating the previously reported circumferentially depleted tracks beneath the slider rails. In the timeframe of our experiment, no significant net lubricant loss was observed.     

Efficient Generation of Microwave Oscillations at Harmonics of the Conductance of a Gunn Diode

Basic characteristics of prototype oscillators operating at the second (19 GHz) and third (36 GHz) harmonics of the negative conductance of a 3715 Gunn diode are presented. The output power of these oscillators is 1.5–8.0 mW and the range of electronic frequency tuning is up to 390 MHz.     

Automated Devices for the Testing of Mill Rolls

Multichannel -type devices developed at TsNIITMASh for the automated ultrasonic inspection of cylindrical objects, such as mill rolls, shafts of turbines and compressor units, circular welded joints of thick-walled shell rings, etc., are described. These devices feature from two to eight acoustoelectronic channels. Acoustic contact occurs through industrial water. The testing is performed under workshop conditions; the object being inspected is rotated by a turning lathe or any other handling mechanism. Sonication is simultaneously performed by piezoelectric transducers (PETs) with input angles of 0, 40, 50, 60, and 70° and also by surface and head waves in order to reveal surface and subsurface flaws. A wide-span eddy-current transducer of special design is also used for this purpose. All data are stored in flash memory and retrieved on a PC located in an office. The inspection results are displayed as C- and B-type scanning defectograms. Moreover, it is possible to obtain an isometric image of flaw zones. -type devices have been used for over one and a half years in two workshops at OAO Severstal'.     

Nano/microtribology Stick-Slip Number Under an Atomic Force Microscope and Its Characteristics

The atomic force microscope (AFM) has become a main instrument in observing nano/microtribological characteristics of sample surfaces. In this paper, we investigated the micro-scale adhesive contact between the AFM tip and the sample surface based on the Maugis–Dugdale contact model, and analyzed the energy conversion and dissipation process during the AFM scanning process. A dimensionless stick-slip number = 8U₁h²/(kR_s ²) was defined, which can serve as a characteristic index for the appearance of nano/microtribology stick-slip behavior. If the stick-slip number is less than one, i.e., <1, the AFM tip slides on the sample surface and no stick-slip behavior occurs in the AFM lateral force signal. When the stick-slip number equals one, i.e., = 1, the tip jumps on the sample surface and the AFM lateral force signal begins to exhibit a stick-slip behavior but without energy dissipation. Only in the case of >1 does the stick-slip behavior appear in the AFM lateral force signal accompanied by an obvious energy dissipation. The defined stick-slip number demonstrates that the nano/microtribological stick-slip behavior is due to the adhesive hysteresis as well as the instability motion of the AFM tip during the scanning process. Finally, the influence on nano/microtribology stick-slip behavior of sample surface energy, surface topography, scanning velocity, spring constant of AFM cantilever probe, etc. are investigated theoretically and experimentally. Various experimental results of nano/microtribology stick-slip behavior under AFM are successfully interpreted according to the stick-slip number.     

A Position-Sensitive Detector for the Polarized-Neutron Spectrometer

A linear detector of thermal neutrons, developed at the Laboratory for High Energies (Joint Institute for Nuclear Research), is used in the polarized-neutron spectrometer of the -2 reactor (JINR). The data are acquired in the regime of frame-by-frame survey to select neutrons with a wavelength = 1–12 Å by the time of flight. The neutron-detection efficiency is 70% for a wavelength of 2 Å. The detector exhibits a low sensitivity to -rays, a differential nonlinearity of 1.5%, and a spatial resolution of 1.5 mm at counting rates of 10⁵events/s.     

A Shipborne Laser Fluorimeter for Studying Sea-Water Fluorescence Spectra

A shipborne laser fluorimeter making it possible to determine promptly the concentration of chlorophyll A in sea water is described. The measurement error is 35% at chlorophyll concentrations of 0.1–3 g/l, and the single-measurement duration is 1 min.     

A molecular beam study of the tribological chemistry of dialkyl disulfides

Molecular beam studies carried out in ultrahigh vacuum show that dimethyl disulfide reacts with initially clean iron to evolve methane. The reaction is proposed to proceed via a methyl thiolate intermediate. Reaction ceases at 600 K, an effect that is proposed to be due to the surface being blocked by an overlayer of sulfur and carbon. Reaction recommences above 950 K as sulfur diffuses into the iron. The activation energy for the film-forming reaction is 52.5±2.1 kcal/mol, in good agreement with the activation energy for the growth of FeS films from dimethyl disulfide at higher pressures measured using a microbalance. A depth profile of the film grown in ultrahigh vacuum shows that the sulfur-containing film grows on a Fe+C underlayer. Similar molecular beam experiments with diethyl disulfide suggest the formation of an intermediate ethyl thiolate species which decomposes via a -hydride elimination reaction to evolve ethylene. The activation energy for film growth, in this case, is 60±2.4 kcal/mol. The results of tribological experiments using a pin and v-block apparatus are consistent with FeS forming the anti-seizure film.