2009

Grunin A. V., Donskoi E. N., Zalyalov A. N., Ivanov G. A., Kovshov K. N., Lazarev S. A., Petrushin O. N., Tarasov M. D.  Experimental and computational determination of the dose characteristics of a standard source of  γ - radiation  //  Atomic Energy, 2009, Pages 1 - 4 Article in Press

RFNC - VNIIEF, Sarov, Russian Federation

The absorbed dose in a calorimeter is compared with Monte Carlo calculations for a standard source of exposure dose of   γ - radiation from ⁶⁰Co.  It is shown that if the initial γ - radiation spectrum is known to a high degree of accuracy, then a mathematical model of the interaction of particles and γ - rays with matter can be used to calculate the absorbed dose in a detector and the exposure dose in air to within several percent. This makes it possible to develop an experimental - computational method of transferring the dimensional units for the exposure dose and dose rate from a static standard to working means of measurement and pulsed bremsstrahlung sources.

Generalov L. N., Abramovich S. N., Vinogradov Yu. I.  Measurement of the excitation function for the ⁷Li ( t, p ) ⁹Li  reaction using detection of delayed neutrons  //  Bulletin of the Russian Academy of Sciences: Physics, 2009, Volume 73, Issue 2, Pages 156 - 160

RFNC - VNIIEF, Sarov, Russian Federation

The excitation function for the ⁷Li ( t, p ) ⁹Li  reaction is measured at the EGP - 10 electrostatic tandem accelerator ( VNIIEF ) at the incident triton energies Et = 5 - 11,3 MeV.  The measurements were based on detection of delayed neutrons resulting from the decay of  ⁹Li  nuclei. The neutrons were detected by the 4π detector consisting of  ³He  counters enclosed in a polyethylene moderator. A pulsed mode was used for irradiating the LiF target ( 210 µg cm^-2 ) of natural isotopic composition on the tantalum backing. Absolutization of the excitation function was performed against the ⁷Li ( p, n ) reaction cross sections.

Kudasov Yu. B.  Magnetic phase diagram of frustrated spin - chain compounds   //   Bulletin of the Russian Academy of Sciences: Physics, 2009, Volume 73, Issue 1, Pages 22 - 24

RFNC - VNIIEF, Sarov, Russian Federation

The magnetic ordering in frustrated triangular lattices of Ising chains is discussed. It is shown that the differences in the low - temperature CsCoCl₃, Ca₃Co₂O₆  and  Sr₅Rh₄O₁₂ phases are related to the interaction between the next - to - nearest pairs of chains, which partially lifts the degeneracy of the ground state of the 2D antiferromagnet Ising model. In zero magnetic field and at low temperature, a stripe structure arises in the new compound Sr₅Rh₄O₁₂.

Babich L. P., Loiko T. V.  Subnanosecond pulses of runaway electrons generated in atmosphere by high - voltage pulses of microsecond duration   //   Doklady Physics, 2009, Volume 54, Issue 11, Pages 479 - 482

RFNC - VNIIEF, Sarov, Russian Federation

A study was conducted to demonstrate subnanosecond pulses of runaway electrons ( RE ) generated in atmosphere by high -voltage pulses of microsecond duration. A smallsized generator including a pulse raising transformer was developed and used as a source of highvoltage pulses. The generator was calibrated in the voltage range of 30 - 110 kV through standard copper spherical discharger with sphere diameters of 12,5 cm. UV irradiations was used for stabilizing the breakdown in the air gap between the spheres. The calibration was carried using the voltage divider TEKTRONIX P60115A, guaranteeing the dividing factor of 1000, accuracy of 3%, a pass - band of 75 MHz, and the maximal pulse voltage of 40 kV according to the data in the divider characteristics sheet. The study also investigated processes in the atmosphere under the action of pulses of microsecond duration.

Babich L. P., Bochkov E. I., Kutsyk I. M.  Numerical simulation of a conducting channel initiated by an extensive air shower in a thunderstorm electric field  // Geomagnetism and Aeronomy, 2009, Volume 49, Issue 2, Pages 232 - 238

RFNC - VNIIEF, Sarov, Russian Federation

The mechanism by which lightning is initiated by preliminary ionization of the atmosphere by extensive atmospheric showers ( EASs ) of cosmic particles with the following development of relativistic run - away electron avalanches ( RREAs ) is analyzed. The two - dimensional numerical model of conducting channel evolution in a thunderstorm electric field has been constructed. The calculations, performed for different field strength values, energy initiating cosmic particle EASs, and dimensions of the region occupied by the field indicate, indicate that lightning discharges cannot be initiated by a joint action of EASs and RREAs.

Gerasimov A. I., Bubnov V. P.   A device for continuous remote monitoring of the electric strength of insulating oils   //  Instruments and Experimental Techniques, 2009, Volume 52, Issue 5, Pages 707 - 711

RFNC - VNIIEF, Sarov, Russian Federation

A device intended for testing the electric strength ( ES ) of insulating oil in electrical - engineering ( electrophysical ) equipment is described. The probe is a system of many identical electrode elements mounted with alternate polarities with a gap of 0,5 cm between them, so that all elements with the same polarity are connected in parallel. The total area of elements of the same polarity is > 7000 cm². Before measurements of the ES, the experimental relationship between the current through an oil layer between electrodes and the liquid-breakdown voltage, which changed from 15 to 90 kV, was preliminarily determined at a potential difference U = 500 V between electrodes. Subsequently, the change in the current through oil at  U = 500 V  allowed evaluation of the breakdown voltage from the calibration curve. The promptness ( several seconds ) of remote ES measurements with the possibility of automating them according to a chosen program has been confirmed.

Borissenok V. A., Novitskii E. Z., Simakov V. G.   A pyroelectric detector of pulsed  γ rays  //  Instruments and Experimental Techniques, 2009, Volume 52, Issue 4, Pages 523 - 535

RFNC - VNIIEF, Sarov, Russian Federation

A theory of a pyroelectric pulsed - γ - ray detector and results of experimental tests thereof are presented. The detector contains a capacitor, which is filled with a dielectric made of a polarized ferroelectric material that serves as a sensitive element; does not require external power-supply units; and has a temporal resolution of up to 10^-9 s, a sensitivity of ~ 10^-8 C·Gy^-1, an amplitude characteristic linear in the range of absorbed doses 10^-1 - 5·10³ Gy, and high radiation stability and noise immunity.

Vilkov Yu. V., Kravchenko A. S., Saitkulov M. M., Selemir V. D., Terekhin V. A., Tyutyaev A. A.  Studying a spark discharge in the ground during reproduction of a negative lightning - current pulse using magnetic cumulation generators  //  Instruments and Experimental Techniques, 2009, Volume 52, Issue 2, Pages 221 - 225

RFNC - VNIIEF, Sarov, Russian Federation

Using an energy source based on a single BMО - 160 generator, a current pulse with an amplitude of 50 kA and a rise time of 2 µs has been formed in a grounding rod electrode with a length of 1 m in the ground with a resistivity of 160 W m. The maximum length of spark channels on the ground surface from the point of current injection is 3 - 4 m. An energy source based on two BMО - 160 generators connected in series allows an increase in the current pulse amplitude to 90 kA, the rise - time duration being the same, 2 µs. In this experiment, the maximum length of spark channels on the ground surface from the point of current injection exceeds 8 m.

Kudasov Yu. B.  Magnetic structure and phase diagram of  Sr₅Rh₄O₁₂  frustrated Ising magnet   //  JETP Letters, 2009, Volume 88, Issue 9, Pages 586 - 589

RFNC - VNIIEF, Sarov, Russian Federation

The magnetic structure of  Sr₅Rh₄O₁₂  is based on Ising chains of rhodium ions with a variable valence, Rh³⁺ - Rh⁴⁺.   The ordering in the chains is assumed to be ferromagnetic. It has been shown that the magnetic structure and phase diagram of Sr₅Rh₄O₁₂ are well described in a model taking into account weak antiferromagnetic interactions between the nearest and next - nearest neighbors on the triangular lattice of ferromagnetic Ising chains. The ground state at low temperatures is the two - sublattice stripe phase; this phase in the magnetic field is transformed to the ferrimagnetic phase and, then, to the ferromagnetic phase. Small plateaus can be observed in the region of the transition from the ferrimagnetic phase to the ferromagnetic one.

Arinin V. A., Tkachenko B. I.   Achieving the ultimate quality of image registration in radiography  //  Pattern Recognition and Image Analysis, 2009, Volume 19, Issue 1, Pages 63 - 68

RFNC - VNIIEF, Sarov, Russian Federation

In radiography, the quality of obtained images depends mainly on two factors, i. e., the dose absorbed by an object and the quantum efficiency of registration. Increasing the dose is extremely undesirable in medicine; in technical radiography, it constitutes a serious scientific and technical problem concerned with creation of a powerful X - ray apparatus. In connection with this, the problem of increasing the quantum efficiency of registration is highly urgent, most notably in technical radiography, where radiation with a hard spectrum is used and typical quantum efficiency sometimes amounts to only 1 - 2%. To achieve an effectiveness close to 100% ( the ultimate quality of registration ), it has been proposed to use, not a unit element, but rather several uniform or nonuniform elements, i. e., a packet, as a recorder.