Vol 61, No 3 (2018)

The characteristics of a beta spectrometer that consists of a total-absorption Si(Li) detector and a drift Si detector are presented. Using this spectrometer, it is possible to efficiently separate β radiation of nuclei from concomitant X and γ rays. The method is based on coincidences between signals from the thick and thin detectors. The spectrometer can be used to precisely measure the shape of the β spectra of various radioactive nuclei, in particular, of the ¹⁴⁴Pr nucleus, which is the most promising antineutrino source for searching for neutrino oscillations into a sterile state.

A 64-channel readout and data-acquisition module is described in detail. It consists of an H12700 multianode photomultiplier tube, four PADIWA preamplifier boards, and a TRB v3 card that perform the functions of a time-to-digital converter and a data concentrator. The software modules that are necessary for operation of the prototype are described. The inter-channel delays are calibrated. The drift of individual delays does not exceed 0.5 ns for the entire measurement time. The spectra of the “time over threshold” (ToT) are investigated. The influence of periodic noise pickups and the need to improve circuit designs are revealed. The timing properties of the wavelength shifter and its effect on the detection efficiency for Cherenkov rings are investigated. The most intense component is characterized by a decay time of 1.1 ns and there are components with characteristic times of 3.8 and 45 ns. The influence of single-electron spectrum features on the detection efficiency for photoelectrons and the probability of false hits are determined. The total time resolution of 131 channels is 1.1 ns (FWHM). The results make it possible to use the investigated system of readout and data acquisition in the CBM experiment. Nevertheless, the elimination of the revealed shortcomings will provide the efficiency margin and improve the reliability of the system during long-term operation.

A CAMAC (1M) single-channel time-to-digital converter has been designed for measuring time intervals with a time resolution of 2 ns in the range from 0 to ~131 μs. This range can be extended by connecting an additional external counter. This converter is of the counting-pulse type with a calibrated conversion scale. A recirculation generator based on a K500LM101 chip is used as a source of counting pulses. One time interval can be measured at once. Several time-to-digital converters can be combined into a multistop measuring system to increase the number of time intervals recorded by a single Start signal. The differential nonlinearity is 1%, and the integral nonlinearity in the above range is 0.001%. The relative instability of the conversion coefficient caused by supply-voltage variations within the range of–6 V ± 2.5% is 0.24%. The temperature drift of the conversion coefficient in the temperature range of 22.6–65.7°C is 0.07%/°C.

The results of investigations of new semiconductor devices, reverse switch-on dynistors dynistors–diodes (RSDDs), with an operating voltage of 2 kV and a 50-mm diameter of the structure are presented. Their comparison with conventional RSDs shows that the losses in RSDDs are approximately 2 times lower when high-power reverse-current pulses are switched, the losses are virtually the same during switching, and the losses are 15–20% higher when switching rapidly rising forward-current pulses. The limiting abilities of RSDDs are determined when switching unipolar current pulses with a duration of 300 μs: 30 and 100 kA in the reverse and forward directions, respectively. The possibility of reliable switching of alternating slowly damped current pulses with a duration of 40 μs and amplitudes of the first forward and reverse half-waves of 90 and 65 kA, respectively, with which conventional RSDs cannot operate, is shown.

The influence of the diameter of a light beam, the duration of an input pulse, and the velocity of propagation of elastic waves on the formation of the signal at the output of an acousto-optic delay line (AODL) with direct detection is discussed. The specific features of the use of the classical method for calculating the AODL output response are considered. It is shown that the classical method can be used to calculate the output signal only when the duration of the input pulse is greater than the time constant of the AODL.

A circuit of a clock oscillator is proposed, whose frequency and phase are synchronized with an industrial 50-Hz power network. The synchronization with the network reduces the effect of network-interference impact on signals of low-power sensors during their reproduction, measurement, and processing. The device, which was built using several STTL chips, is a frequency multiplier that is based on a phase-synchronization system with a frequency divider in the feedback loop. Due to the phase–frequency principle of the error-signal formation, the danger of capture at multiple frequencies is eliminated and an extended synchronization band is achieved without parasitic frequency modulation of the generated pulses. The device is powered with a +5-V source and has a synchronization band of ±25% of the rated network frequency. The frequency multiplying factor, which in the described embodiment is 65536 (the clock frequency is 3276.8 kHz), can be set arbitrarily via a conjugate change of the frequency-divider modulus and the oscillator center frequency.

The results of testing near-infrared photodetectors, that is, a HAMAMATSU H10330B-25 photomultiplier tube (PMT) and a receiving module that was created by the authors on the basis of an SPAD PGA-284 avalanche photodiode, are presented. The results show that when weak optical signals are registered with an avalanche-photodiode-based detector, its sensitivity is higher than that of the PMT by one order of magnitude, while its maximum counting frequency is 10 times lower.

The design philosophy and output radiation parameters of single frequency TEA CO₂ laser with bleaching intracavity longitudinal modes selector (cell filled with SF₆) are described. At cavity tuning to 10P(16) line and choosing optimum SF₆ pressure in the cell the stable single frequency lasing is realized with scatter of radiation peak power in a series of “shots” less than ±7% of average value. The radiation energy density and intensity gradually tuned in the ranges 0.36–12.5 J/cm² and 2.9–100 MW/cm² correspondingly were realized in the focal plane of a lens with f = 127 mm.

The problems that arise during the calibration of the reference plates of large-aperture interferometers are discussed and the methods for solving them are presented. It is shown that the repeatability of shapes of the reference plates after their rearrangements can be provided by selecting the mechanism of their fixing in place. It is demonstrated that the temperature deformations of the reference-plate surfaces can be determined from a numerical model. These measures have made it possible to calibrate the reference plates of the 630-mm interferometer with an accuracy of λ/1000 RMS (λ = 632.8 nm).

An X-ray detector with a dielectric (KU1 optical glass) used as a sensitive element is described. Operation of the detector is based on the discovered effect of electric-field generation in a dielectric under exposure to radiation. The measurements were taken at the Angara-5-1 facility, at which the radiation source is megaampere Z-pinch plasma. It is shown that when the radiation power incident on the detector is approximately 1 MW/cm², the detector response is a few volts with a time resolution of 1–2 ns. This effect is thought to be caused by “hot” electrons induced by radiation in the dielectric. The estimates for these experimental conditions are presented.

The design of a controlled damper on the basis of a magnetorheological elastomer is described. The technique of determining the dynamic characteristics of the damper, such as the stability, the time constant, and the positioning error, in an active step-by-step displacement mode is presented. A dynamic model of the automatic-control system of the controlled damper is described. The results of experimental studies of the damper start-off current, which amounted to 0.05 A, and the transient process during movement from one point to another (the error does not exceed 2 μm) are presented.

We report on the implementation of the low cost multiple high power light-emitting diodes (HPLEDs) as illumination source for particle image velocimetry measurements in a water tank. The illumination system consists of a custom-built circuit developed using off-the-shelf components for driving the HPLEDs beyond its recommended rating. Two 20 W green LEDs were employed as the pulse illumination light source. The incoherent light generated by the LEDs is channeled into a fiber optic bundle linked to a cylindrical lens for light sheet generation. The light produced by the LEDs was first characterized in term of its wavelength and illuminance properties with respect to input power and pulsing frequency. The complete system was then evaluated by studying the flow around NACA 0018 airfoil in the water tank filled with the seeding particles. The developed system was able to capture the flow field generated by the airfoil when moving at various attack angles. Images acquired using both laser-based and HPLEDs based illumination systems are compared. The results obtained demonstrate the feasibility of the developed low cost HPLED illumination system.

The purification of tin via the difference in the behavior of impurities in its metallic and semiconductor solid phases has been investigated.

A two-chamber metal cryostat with a volume of six liters of liquid helium for neutron and optical studies of impurity gel samples in liquid helium was designed. The cryostat allows long-term, up to 20 h, measurements at helium temperatures without adding liquid helium to it. The sample preparation site in the cryostat is spaced (the working cell is raised up) with the location of the working cell during the research (the cell is shifted down to the cryostat tail). The samples are prepared by condensing gaseous ⁴Не with a small admixture of vapors of an investigated substance on the surface of superfluid He-II in a quartz-glass cell at a temperature of 1.8 K. Transparent quartz-glass windows in the upper part of the cryostat make it possible to observe the process of preparing an impurity gel sample in the working cell. The quartz windows in the bottom part (tail) of the cryostat are intended for adjusting the position of the working cell and carrying out optical research. Subsequently, in a modernized cryostat design for neutron studies, the tail shell with the optical windows was replaced by a continuous thin-walled cup that was turned from an aluminum billet. The results of studying the transmission and small-angle scattering of cold neutrons in water-gel samples in superfluid and normal ⁴Не are presented for illustration.