X-ray flash radiography system for a high-current discharge in a dense gas

An X-ray diagnostic system for determining the metal vapor concentration in a high-current pulsed discharge in a high- and ultrahigh-pressure gas based on a pulsed X-ray source in a spectral region of 20–50 keV and an X-ray CCD camera has been designed. Two nanosecond generators with durations of high-voltage pulses of 10–20 and 50 ns and new through-target-type X-ray tubes were used. Experiments on the diagnostics of a high-current discharge in an axially symmetric electrode system have been performed at dJ/dt = 10⁹–10¹¹ A/s and discharge currents <1 MA. The data on the spatial distribution of metal vapors injected from the electrodes as a result of erosion are obtained.     

A laser ion-mobility spectrometer

The process of ion-packet broadening in a longitudinal laser spectrometer of ion mobility is studied. The contributions of the diffusion, Coulomb, and other broadening mechanisms are compared. The resolution of the developed spectrometer was measured (R ∼ 45) in atmospheres of both purified air and pure nitrogen. The dependence of the spectrometer resolution on the drift voltage was studied. The recorded spectra of a number of molecules of explosives with an extremely low pressure of saturated vapors indicate a high sensitivity of the developed spectrometer (no worse than 10⁻¹⁴ g/cm³). Original Russian Text ? G.E. Kotkovskii, I.L. Martynov, V.V. Novikova, A.A. Chistyakov, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 2, pp. 110–116.     

CdTe-based detectors for recording X-ray pulses with a subnanosecond resolution

Characteristics and manufacturing methods of semiconductor detectors made of pressed cadmium telluride are given. The sensitivity of the detectors is ∼(1–5) × 10⁻¹⁹ A cm² s/quantum. SPPD29k and SPPD29-02 detectors are calibrated by subnanosecond X-ray pulses generated by the СПИН-2 accelerator. The measured pulse durations are τ_0.5 = 0.29 and 0.47 ns, respectively. The X-ray pulse shape of the APCA accelerator is recorded.     

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.     

A distributed fiber-optic position-sensitive detector of an electric arc

A distributed fiber-optic position-sensitive detector for detecting an electric arc by optical radiation at an illuminance of ∼10⁵ lx, a fiber length of 25 m, and an arc location error of 1 m is described. Original Russian Text ? Yu.P. Kazachkov, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 2, pp. 145–147.     

Application of a monopulsed repetitively pumped Nd:YAlO3 laser for photothermoplastic recording of stroboholographic interferograms

A version of the stroboholographic interferometry method with a photothermoplastic recording medium is described. Its distinguishing feature is the use of a repetitively operating monopulsed laser as an illumination source. The performance characteristics of the developed highly coherent frequency-doubled Nd:YAlO₃ laser with combined modulation of the cavityQ-factor by an acoustooptical shutter and a bleachable filter are presented. A system for synchronization of the monopulses with the required phases of the periodical process under study is described. It is shown that, when using the ΦTпH-Л photothermoplastic medium, recording of double-exposure stroboholographic interferograms of diffusely reflecting objects ∼40×90 mm in size is ensured by 10–16 laser pulses at an output energy of ∼4×10⁻⁴ J and a repetition rate of no more than 10 Hz. Interferograms of larger objects can be obtained by increasing the pulse energy and the laser firing rate. Deceased.     

On the DMT theory

The frequent claim that the Tabor parameter μ governs the transition from the DMT theory to the JKR theory is investigated. The change from the simple surface force law σ ∼ A/h ³ of the DMT theory to the Lennard–Jones law σ ∼ A/h ³–B/h ⁹ of the MDT theory and the numerical solutions is noted, and the ‘adhesive force’ is evaluated for both laws. Except in the limit of zero Tabor parameter, when the Derjaguin theories reduce to the rigid-sphere model, the predictions are consistently worse than assuming the sphere to be rigid. A ‘semi-rigid’ sphere model is proposed, which correctly describes the asymptotic behaviour as μ → 0, but leaves a considerable gap before the JKR theory can be applied.     

A plasma generator based on nonself-sustained low-pressure glow discharge with a large-volume hollow cathode

The results of studying nonself-sustained glow discharges in an electrode system with a hollow cathode with a volume of 0.25 m³ are presented. A high-current (up to 35 A) nonself-sustained glow discharge at low pressures (0.3–1.0 Pa) is initiated and sustained with the help of an auxiliary cold-hollow-cathode arc discharge. When the current of a nonself-sustained glow discharge increases from 2 to 35 A, its burning voltage changes from 40 to 300 V. These values are much lower than the voltage for a self-sustained glow discharge in the same electrode system. At a discharge current of 30 A, the electron concentration at the center of the hollow cathode is n _e ∼ 10¹⁰–10¹¹ cm⁻³ and the electron temperature is T _e ≈ 2 eV. The discharge considered can be used in the system for modification of materials and products.     

A dilution microcryostat-insert

An autonomous dilution microcryostat in which ³He circulates due to its condensation in the volume cooled by sorption evacuation of ³He from a separate bath. A specific feature of this apparatus is the position of the sample holder in its upper part, which facilitates access to it. The holder is connected to the mixer through a heat conductor made from annealed copper wire with a length of ∼0.5 m. The cryostat operates while inserted into a nitrogen-free portable (35 l) helium-filled vessel. The operating cycle of the cryostat includes the procedures of desorption, condensation, and cooling of the ³He-filled bath to 0.35–0.40 K and the mixer to 0.05–0.10 K (lasting ∼1.5–2.0 h) and also a period of maintaining the temperature below 0.1 K (12–14 h). The amount of liquid helium in the portable cryostat is sufficient for operating for 6 days. The lowest reached temperature of the holder is 0.04 K. When the power dissipated in the holder is 0.5 μW, its temperature does not increase above 0.1 K. The instrument is mainly designed for cooling sensitive radiation detectors. Original Russian Text ? V.S. Edelman, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 2, pp. 159–165.     

Energy dependence of the relative light output of YAlO<Subscript>3</Subscript>:Ce,Y<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Ce,and YPO<Subscript>4</Subscript>:Ce scintillators

The nonlinear dependence of the relative light output on the energy deposited in single-crystal scintillation materials YAlO₃:Ce (YAP:Ce), Y₂SiO₅:Ce (YSO:Ce), and YPO₄:Ce (YPO:Ce) has been studied. The investigations have been conducted under quasi-monochromatic X-ray excitation in the energy range of 9.5–100 keV. In addition to the standard technique for measuring the nonproportional scintillator response based on the dependence of the full-energy peak position on the energy of incident radiation, a method is proposed for measuring the light output by X-ray fluorescence peaks. Using this method for YAP:Ce, it is possible to investigate the nonlinear dependence of the light output on the photon energy in the energy range of 2–40 keV. Along with this method, the K-dip spectroscopy method has been proposed and tested by measuring the dependence of the relative light output on the electron energy in the range of 0.1–80.0 keV. The processes resulting in the loss of the scintillation material efficiency at a high ionization density are considered.     

A 3He cryostat inserted into a refrigerator with an impulse tube

A compact autonomous ³He cryostat inserted into a two-stage refrigerator with an impulse tube is described. The cryostat contains baths filled with ⁴He and ³He and evacuated with cryosorbers to temperatures of ∼1 and ∼0.35 K, respectively. The low temperature is maintained for 6–8 h at an amount of liquid ³He filling the cryostat of ∼0.035 mol. The dimensions of the insert (below the upper flange) are 49 mm (diameter) and 720 mm (length). The insert is introduced into a hermetically sealed tube-well filled with a heat-exchange gas during operation, which promotes the heat removal to levels of 45–50 K (the first stage of the impulse tube) and 3–4 K (the second stage of the impulse tube). The cryostat can be mounted in and extracted from both the warm cryostat and the cryostat cooled to low temperatures.     

A method of controllable pulse-heating for investigation of properties of short-lived liquids

A method of controlled pulse heating of low-inertia thermal probe immersed into the liquid under study with a temperatureT ₀ is described. The control system provides a “temperature plateau”-type heating mode, which consists in a rapid (t ₁∼10 μs) increase in the mass-average probe temperature to a chosen valueT _pl ≫T ₀ and maintains this value for a certain time interval (t ₂∼10³–10² μs) to within 1 K. Thermal effusivity of the substance, in relative units, is determined from the value of its internal heat flux. Sensitivity to changes in the thermal effusivity of a reference substance was 10⁻⁴. Due to the short pulse length and fine tuning of theT _pl value, the method allows one to conduct step-by-step scanning of “instantaneous” thermal properties of a substance in the region of its short-lived states.     

A high-current picosecond electron accelerator with a low-impedance vacuum diode

A high-current picosecond (∼150 ps) electron accelerator with a beam energy of 50–100 keV is described. The use of a low-impedance vacuum diode at an amplitude of the arriving pulse of 300–400 kV made it possible to significantly increase the beam current (up to ∼15 kA) and the corresponding X-radiation intensity. One of the accelerator's applications in the X-ray therapy of malignant tumors. Some computational relations and results of measurements of the arriving and reflected voltage pulses near the diode are presented. The electron-accelerating voltage, beam current, vacuum-diode impedance, and other parameters are determined after the recovery procedure.     

A low-voltage ionization chamber for the ITER

An ionization chamber with an operating supply voltage of 10 V has been designed for use at the ITER. The sensitivity of the chamber filled with air at atmospheric pressure is 100–200 times higher than the sensitivity of the chamber pumped down to a pressure of 10⁻³–10⁻⁴ Torr. It is shown that application of the supply voltage modulation technique allows the pickup noise to be substantially reduced; as a result, the amplifier can be located at a large (70–100 m) distance from the chamber. Results of the experiments aimed at testing this technique on the T-10 facility are described. Original Russian Text ? Yu.V. Gott, M.M. Stepanenko, 2009, published in Pribory i Tekhnika Eksperimenta, 2009, No. 2, pp. 117–121.     

Discrimination of particles by the scintillation pulse shape in the range of low energies (6–100 keV for electrons) using the linear filters

The use of the linear filters for particle discrimination by the scintillation pulse shape is considered. The particle separation process has been simulated by the Monte Carlo method, taking into account that the slow scintillation component decays according to the hyperbolic law and that its relative contribution is energy dependent. The best figures of merit of particle discrimination attainable with this technique have been obtained assuming that the PMT and electronic noises are zero. It is shown that, by contrast to the zero crossing method, pulse shape discrimination of particles using the linear filters can ensure rejection of the γ-ray background to a level of ∼10⁻⁴ at particle energies of up to 12 keV of the electron equivalent. For energies of <24 keV, it is expedient that the signal acquisition time be increased to a few microseconds.     

A detector for imaging of explosions on a synchrotron radiation beam

Synchrotron radiation (SR) offers a unique chance to study the structure of a substance in fast processes. Since SR is emitted by electron bunches in a storage ring, the SR burst corresponding to a single bunch may be very short. Should a detector capable of detecting SR from a single bunch without mixing signals from different bunches be available, it is possible to obtain information on changes in the state of the material in a sample under investigation with a very high time resolution. A detector for imaging of explosions on an SR beam—DIMEX—has been developed by the Budker Institute of Nuclear Physics (Siberian Division of the Russian Academy of Sciences, Novosibirsk). This detector is a high-pressure ion-ization chamber with a strip readout at a pitch of 0.1 mm. The electron component of primary ionization is collected within 50 ns, which is substantially shorter than the orbital period of a bunch in the VEPP-3 storage ring (250 ns). The DIMEX is filled with a Xe—CO₂ mixture (3: 1) at an absolute pressure of 7 atm. The spatial resolution of the detector is ∼210 μm, and its efficiency for radiation with an energy of 20 keV is ≥50%. The dynamic range of the detector is ∼100, which allows one to measure the signal with an accuracy of ∼1%. In this case, the maximum flux of X-ray photons, at which the DIMEX operates in a linear region, is ∼10¹⁰ photons/(channel s). Today, the detector has been used in experiments aimed at studying evolution of the density in detonation waves and processes of nanoparticle production at the VEPP-3 storage ring by employing the small-angle X-ray scattering technique.     

A low-temperature capacitive dilatometer

A dilatometer with a capacitive displacement sensor intended for measuring the thermal expansion of solid samples in a temperature range of 4–300 K is described. The sensor of the instrument was mounted inside of industrial insert VTI SIV with controlled circulation of liquid helium encased in portable cryostat and was successfully used jointly with a simple commercial temperature control system. The dilatometer allows studies of the thermal expansion of samples with a sensitivity of ∼1.4 ? in consecutive cooling and warming cycles with a rate of ∼10⁻³ K/min. The results of measuring the thermal expansion of a CoS₂ sample near the phase-transition point are presented.     

Discrimination of particles by the scintillation pulse shape (in the electron energy range of 0.5–4.0 MeV) using the zero-crossing method

The ratios of the fast to slow components of scintillation pulses produced by neutrons and γ rays have been calculated on the basis of experimental data for several energies in the range of 0.5-4.0 MeV of the electron equivalent. The procedure for discriminating between neutrons and γ rays by measuring the zero-crossing time of a bipolar pulse formed by RC circuits has been simulated for organic scintillators using the Monte Carlo method in the range of 0.012-4.000 MeV of the electron equivalent. It is shown that pulse shape discrimination of particles based on the zero-crossing technique allows rejection of γ-ray background down to a level of 10-4 at particle energies of >100 keV of the electron equivalent (for energies of <50 keV, the γ-ray background is suppressed to a level of 10^-1- 10^-2 and this technique becomes ineffective in principle).     

A Wideband spectrometer for NMR studies

The design of a wideband decimeter-wave (200–900 MHz) spectrometer with a magnetic induction of up to ∼10 T is described. This spectrometer is intended for studying electronic-nuclear oscillations in antiferromagnets at low temperatures (4.2−1.3 K). Critical field H _c = 2.5 ± 0.3 T of a reorientation transition in a noncollinear antiferromagnet Mn₃Al₂Ge₃O₁₂ at temperature T ≈ 1.3 K was determined from a ⁵⁵Mn²⁺ NMR spectrum.     

A two-frequency pulse refractometer for measuring the electron density in tokamaks

An instrument for fringe-jumps free measurements of the electron concentration and estimations of the peaking factor of density distributions in magnetic confinement plasma devices with probing at frequencies close to the cutoff is described. The instrument is intended to perform measurements in a 5 × 10¹⁸–10²⁰ m⁻³ density range (while probing by the extraordinary wave) with time resolution ∼10 μs.