Том 61, № 1 (2018)

While preparing for an experiment on the search for neutrinoless double β decay of ¹⁵⁰Nd nuclei, the spectrometric properties of polystyrene were investigated, including the dependence of the photomultiplier pulse amplitude on the energy of detected electrons. It is shown that a good description of experimental data is attained by taking the energy loss in passive materials, changes in the ionization density at low energies, and additional light due to Cherenkov radiation generated in polystyrene into account.

The parameters of detectors based on CdZnTe crystals with a sensitive volume of approximately 1500 mm³ are investigated. It is shown that at room temperature the characteristics of these detectors are high enough for spectrometry of γ rays from ²⁴¹Am, ⁵⁷Co, ¹³⁷Cs, and ⁶⁰Co sources.

The application of high-power semiconductor lasers for creating a population inversion in active gaseous media is an integral part of studies that are aimed at the achievement of a sufficient level of laser-radiation energy to initiate a thermonuclear reaction. The stability of the laser radiation and, thus, the repeatability of experimental results, depend on the stability of the parameters of current pulses for pumping laser-diode arrays with a pulse amplitude of up to several hundred amperes. The flow of current pulses with such an amplitude through a cable that connects the load to the output of the current-pulse source must not lead to the formation of voltage pulses of opposite polarity across the load, which can damage it. This can be prevented by correcting the current pulse edges. It is proposed to develop a source of current pulses with a high amplitude on the basis of several modules of fast linear current amplifiers with individual control loops, whose outputs are connected in parallel. It is established that a compensation-type current sensor on the basis of the Hall effect is operable at high frequencies and can be used in these modules, but it has pronounced resonance properties, which must be canceled. It is shown that analog driving pulses of each module can be formed using aperiodic chains with parameters that eliminate oscillatory processes in the load circuit. A dynamic model of a module of the linear current amplifier and the calculation relationships for the parameters of its components, which follow from this model, are presented. The experimental results that confirm stability of the parameters of the formed current pulses are presented.

The possibility of using avalanche photodiodes that operate in the single-photon registration mode as a source of a random physical quantity in generators of random number sequences was evaluated. The operating modes of avalanche photodiodes were determined that allow generation of streams of random events, whose statistical characteristics are similar to those of a Poisson stream. Estimates of the similarity of the properties of generated random binary sequences to the properties of a uniformly distributed sequence are presented.

The parameters in a nuclear magnetic resonance free induction decay (FID) signal contain information that is useful in magnetic field measurement, magnetic resonance sounding and other related applications. A real time sampled FID signal is well modeled as a finite mixture of exponential sequences plus noise. We propose to use the Hilbert-Huang transform (HHT) for noise reduction and characterization, where the generalized Hilbert-Huang represents a way to decompose a signal into so-called intrinsic mode function (IMF) along with a trend, and obtain instantaneous frequency data. First, acquiring the actual untuned FID signal by a developed prototype of proton magnetometer, and then the empirical mode decomposition is performed to decompose the noise and original FID. Finally, the HHT is applied to the obtained IMFs to extract the Hilbert energy spectrum of the signal on the frequency axis. By theory analysis and the testing of an actual FID signal, the results show that, compared with general noise reduction methods such as auto correlation and singular value decomposition, combined with the proposed method can further suppress the interfered signals effectively, and can obtain different components of FID signal, which can be used to identify the magnetic anomaly, the existence of groundwater etc. This is a very important property since it can be exploited to separate the FID signal from noise and to estimate exponential sequence parameters of FID signal.

A power-supply unit for pulsed lasers that are pumped by low- and medium-power flashlamps with long pump pulses that does not require a capacitive storage unit is described. The pump-pulse duration is limited by the radiation and thermal stability of the active elements and pump lamps. A functional diagram of the power-supply unit and a circuit diagram of its power system are presented. The basic parameters and elements of this unit, as well as the results of using a laser with the described power supply in experiments, are presented.

The possibility of identifying radioactive and nuclear materials using TSRM84 radiation monitors with γ-ray detectors based on CsI:Tl scintillators have been investigated.

A new construction of a magnetic system and a circuit for detecting the signal of nuclear magnetic resonance (NMR) in a weak magnetic field are described. The features of NMR-signal detection from a small volume (less than 0.3 mL) of liquid medium in a weak field using the modulation method are determined. Taking these features into account in the new design of the compact NMR spectrometer has made it possible to provide detection of signals from different nuclei of a condensed medium that possess a magnetic moment. The results of the experimental investigations of various condensed media are presented.

An orbital detector of ultra-high energy cosmic rays has been developed by the Skobel’tsyn Institute of Nuclear Physics of the Moscow State University together with the international JEM-EUSO collaboration for mounting on board the International Space Station. Its multichannel photodetector is composed of an array of multianode photomultiplier tubes (MAPMTs) combined into modules with 36 MAPMTs in each and with approximately 10⁵ pixels in total. Since the number of channels is great and the speed of measurements is high, high requirements are set for the system of detection, selection, and analysis of events. The designs of the modular photodetector composition and the network architecture of the data processing system that is capable of performing efficient selection of events with different space−time structures are presented. The network principle is implemented via three types of communications: high-speed links between adjacent photodetector modules, long-distance communications for recording information to the permanent memory, and synchronizing links for timing the operation of individual modules. This digital-processing system of the detector can be designed using the ZYNQ system-on-chip concept that includes a field programmable gate array and a processor system.

A radiometer developed at Budker Institute of Nuclear Physics (Siberian Branch, Russian Academy of Sciences) for diagnostics of the efficiency of the electron cyclotron plasma heating in a mirror magnetic trap (GDT) is discussed. The radiometer is based on the superheterodyne principle. The characteristics of the instrument such as the operating range, sensitivity, frequency and time resolution are adapted to the requirements of the experiments. The receiver is equipped with a system for protection against stray radiation from powerful gyrotrons that are used in the electron cyclotron heating experiments. The radiometric measurements of the plasma self-emission carried out at the GDT facility showed that the new information channel helps to interpret the processes of resonant microwave plasma heating more accurately.

A double-modulation technique was developed and tested experimentally for the detection of the kinetics of reflection of subpicosecond pulses of probe near-IR radiation from a sample (or transmission through it) after the action of exciting radiation pulses. A probe signal is detected at a frequency that is equal to the sum of stabilized unequal frequencies of interrupting exciting and probe radiations, thus permitting the elimination of the contribution of scattered exciting radiation from the valid signal. When detecting the semiconductor- sample reflectance kinetics with a time resolution of 0.13 ps, the reflection sensitivity ΔR/R = 5 × 10^–6 was reached.

When electro-optical chromophores are embedded into a polymer matrix and aligned in a preferential direction, it becomes possible to control the refraction of light in such a composite medium under the influence of an external electric field. This effect is used in the production of high-speed integrated-optical modulators, switches, etc. We manufactured nonlinear optical polymethyl methacrylate (PMMA) films into which the DR13 chromophore was embedded. An algorithm is created that allows one to determine the electro-optical parameters of films in a multilayer anisotropic structure with metal electrodes, when a control voltage is supplied to them. The electro-optical coefficients r₃₃ and r₁₃ of the PMMA/DR13 composite were found at several wavelengths near the DR13 chromophore absorption peak and far from it. The proposed method makes it possible to measure the electric-field-induced change in the refractive index in the thin-film light-guiding structure of an actual electro-optical modulator with an accuracy of ±0.0005.

A technique for studying the magnetic susceptibility of colloidal solutions in a hermetically sealed glass volume (a ferrofluidic cell) is proposed. Experimental investigations have shown that Curie’s law holds in the temperature range of 283–323 K at which ferrofluidic cells are used. A further increase in the temperature of a colloidal solution in a ferrofluidic cell leads to an increase in the Curie constant C, which is due to the fact that the thermal motion of molecules destroys conglomerates with antiparallel magnetic moments of nanoparticles that have a binding energy of the order of kТ.

A calibrating apparatus for spectrometers of the red and near infrared bands based on the analysis of the emission spectra of inert gases is described. One feature of this calibrator is the use of readily available starters for fluorescent lamps as optical emitters. A radio-frequency discharge was used to excite gases in the starters. Starter models (with neon and argon) were selected that made it possible to cover the important spectral band for diode lasers (600–1400 nm) with reference lines. The use of a calibrator as an auxiliary gas-discharge cell for diode-laser absorption spectrometry of low-temperature plasma was demonstrated. When a high-frequency discharge was excited in the starter by an outer ring electrode, a signal of 30% absorption at the 1s₅ → 2p₉ transition of metastable Ar* atoms was recorded with a low noise level. This result is evidence of the possibility of using the calibrator as an optical reference for simple systems of laser-frequency stabilization or for investigating the shifts of spectroscopic lines of Ar or Ne atoms.