A solution is proposed for the the front amplifier of the nuclear quadrupole resonance pulsed Fourier spectrometer, and its noise and signal characteristics are investigated using complex SPICE simulation of the electrical circuit diagram. The study made it possible to carefully analyze the main characteristics of the pre-amplifier and find out the possibilities of its application in the low-frequency region of the short-wave frequency range (2 MHz - 6 MHz), which is attractive for the possibility of identifying spin induction decay signals from explosive and narcotic substances. In particular, the optimal number of parallel-connected active elements of the input stage was investigated, which made it possible to reduce its own noise voltage to 12.8 nV/√Hz, and the modes of operation of the cascades of the entire circuit were determined, which made it possible to achieve a maximum gain of 74 dB at an input sensitivity of 10 V. The frequency characteristics of the amplifier were also studied, the analog bandpass filter and the elements of input and output impedance matching schemes were calculated.
Nuclear quadrupole resonance is one of the express and highly informative methods of experimental research and has a number of practical applications, in particular for pulse detection of explosive and narcotic substances in non-metallic containers, which include the 14N isotope. One of the key problems of equipment of this class is the need to use a specific radio frequency transmitter, which must correspond to the given signal and energy characteristics. The paper proposes an applied solution for the operating layout of such a device for a pulsed Fourier spectrometer of nuclear quadrupole resonance and considers the key aspects of battery power supply. Experimental studies have confirmed that the device provides amplification of excitation signals up to 1.2 kW in the frequency range 100 kHz - 10 MHz and up to 1.7 kW at the resonant frequency 14N - 4.65 MHz.
Using the continuous NQR method with synchronous detection in the sweep mode, in melt-grown layered InSe single
crystals, the 115In NQR spectra were studied for four 115In resonance transitions with spin 9/2, the average values of
which only approximately satisfied the ratio v1:v2:v3:v4 = 1: 2: 3: 4. It is established that for higher-order transitions there is a deviation of the frequency multiplicity. In particular, it is shown that additional lines are observed in multiplet groups for higher-order transitions, which, in our opinion, is due to the presence of hexadecapole interaction of 115In nuclei with the electric field gradient in InSe.
A novel simple autonomous optoelectronic circuit that demonstrate chaotic behavior is presented. In this circuit a lightemitting diode is a simple optoelectronic element. The mathematical model that contain exponential nonlinearity and six terms with two parameters is described by three first-order ordinary differential equations. A great interest is the simulation that using different software environments allows to demonstration different information properties of chaotic oscillations. For modelling of information properties of the chaotic system and demonstrate results was selected one of the modern software LabView (LabView-2015 (32-bit version for Windows). Temporal dependence of the system is discussed, the chaotic attractors are found and the signal spectrum is given.
The influence of the polytypical structure of GaSe on the shape of the EPR spectra of the gadolinium impurity in the Gd3+ state has been investigated. It is shown that in a layered crystal at impurity concentration of about 1018 cm-3 at least
three types of paramagnetic centers appear. The presence of nonequivalent positions of the Gd3+ ion is explained by the presence of polytypic modifications in GaSe. It was revealed that the introduction of a paramagnetic impurity into the crystal significantly expands the NQR spectrum.
The digital control system of pulsed nuclear quadrupole resonance (NQR) Fourier radio spectrometer of laboratory type is developed, the main functional-algorithmic methods of which are implemented in field-programmable gate array (FPGA) Cyclone EP1C12F324. The algorithm of the proposed program and the configuration structure of the IC, created by means of the syntax of modeling the dynamic modes of logical structures on the basis of the finite state machine and functional modules, provide for the adjustment of all necessary NQR operation modes of the spectrometer and the operative control over the performance of the radiophysical experiment. The transfer of commands to the execution units of radiospectrometer at a rate of 3.15 Mbit/s is provided through a 4-bit parallel interface.
The effect of temperature annealing on the shape of the 115In NQR spectra in InSe has been studied. It is shown that with a gradual reduction of annealing temperature the polytype composition of a layered crystal is stabilized, the number of defects and deformation stresses is reduced. On the basis of X-ray diffraction patterns and NQR spectra the character of the block structure of layered crystals is revealed.
A method for quality assessment of layer-structured semiconductor single crystals (InSe, GaSe, GaS) grown in evacuated ampoules by the Bridgman technique is proposed. For this purpose, nuclear quadruple resonance method with a consecutive scanning of the entire sample volume and evaluation of crystal perfection by the resulting spectra is used. Effective interaction between high-frequency field and crystal and, accordingly, restriction of scanning area of sample under study is provided with the use of a two-way saddle-shaped coil for a nuclear quadruple resonance spectrometer.
Pulsed radiospectroscopy method has been used to study nuclear quadruple resonance (NQR) spectra of 69Ga and 115In isotopes in the layered semiconductors GaSe and InSe. It has been found that in GaSe and InSe there is a considerable temperature dependence of NQR frequency which in the temperature range of 250 to 390 K is practically linear with conversion slope 1.54 kHz/degree for 69Ga and 2.35 kHz/degree for 115In. In the same crystals the effect of uniaxial pressure on NQR spectra applied along the optical axis с up to the values of 500 kg/сm2 has been studied. A strong attenuation of NQR spectra intensity with increase in pressure on layered crystal package has been established. The unvaried multiplicity of resonance spectra indicates the absence of structural transformations in these layered crystals over the investigated range of temperatures and pressures.
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