Devices and Methods of Measurements (E-Journal) / Приборы и методы измерений
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ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ЭЛЕКТРИЧЕСКИХ ХАРАКТЕРИСТИК ГЛУБОКОСУБМИКРОННОГО МОП-ТРАНЗИСТОРА СО СТРУКТУРОЙ «КРЕМНИЙ НА ИЗОЛЯТОРЕ»
Get PDFToday submicron silicon-on-insulator (SOI) MOSFET structures are widely used in different electronic components and also can be used as sensing elements in some applications. The development of devices based on the structures with specified characteristics is impossible without computer simulation of their electric properties. The latter is not a trivial task since many complicated physical processes and effects must be taken into account. In current study ensemble Monte Carlo simulation of electron and hole transport in deep submicron n-channel SOI MOSFET with 100 nm channel length is performed. The aim of the study is investigation of the influence of interband impact ionization process on the device characteristics and determination of the transistor operation modes when impact ionization process starts to make an appreciable influence on the device functioning. Determination of the modes is very important for adequate and accurate modeling of different devices on the basis of SOI MOSFET structures. Main focus thereby is maid on the comparison of the use of two models of impact ionization process treatment with respect to their influence on the transistor current-voltage characteristics. The first model is based on the frequently used Keldysh approach and the other one utilizes the results obtained via numerical calculations of silicon band structure. It is shown that the use of Keldysh impact ionization model leads to much faster growth of the drain current and provides earlier avalanche breakdown for the SOI MOSFET. It is concluded that the choice between the two considered impact ionization models may be critical for simulation of the device electric characteristics.
НЕУПРАВЛЯЕМЫЙ ТОК ФОТОЭЛЕКТРОННОГО УМНОЖИТЕЛЯ ПРИ ФОТОЭМИССИОННОМ АНАЛИЗЕ ИЗЛУЧЕНИЯ
Get PDFThe dependence of photon energy from energy of photoelectron is base of photoemission radiation analysis. In such photoemission measurements except current of photocathode is always exist a reverse current from the collector of electrons to the photocathode in two-electrode sensors. There are various ways of reverse and uncontrolled current eliminating or reducing their influence. The constructive method is based on creating an electron-optical system of photoelectronic device, which would be a photoelectron energy analyzer. The second method – technological. However, it requires the manufacture of the photocathode and the dynode system in different vacuum chamber with subsequent connection to a single device in vacuum environment without exposure to the atmosphere. The purpose of this article is to determinate the effect of photoemission from photocathode chamber and the first dynode of photomultiplier on energy distribution of the photoelectrons from photocathode. To solve this problem authors obtained calibration curves for measuring pyrometer module ПИФ 4/2 with ФЭУ-114 as a sensor at supply voltage 1350 V and different decelerating voltages. The effect of illumination on the value of modulation coefficient on temperature k(T) and wavelength k(λ) is shown. In temperature measurements, this effect is evident in fact that at temperatures below 1400 K linear dependence ln k – T-1 is broken. Still this linear dependence is a necessary consequence of the fact that the measured temperature is color temperature. However, this calibration curve can be used to measure low temperature if the target measurements condition and calibration conditions are identical. In wavelength calibration, curve k(λ) at λ > 760 nm is two-valued, that doesn’t allow to identify monochromatic radiation by this method and bring in errors in temperature measurements.
ЛАЗЕРЫ НА КРИСТАЛЛАХ Tm:KLu(WO4)2 и Tm:KY(WO4 )2 В МИКРОЧИП-КОНФИГУРАЦИИ ДЛЯ ДИСТАНЦИОННОГО ЗОНДИРОВАНИЯ АТМОСФЕРЫ
Get PDFDiode-pumped solid-state lasers are attractive for a variety of practical applications in many fields of human activity due to their high efficiency, compactness, and long durability. For applications in remote sensing lasers emitting in the spectral range of about 2 microns are required. Materials doped with trivalent thulium ions are promising active media emitting in this spectral range. Potassium rare-earth tungstates are attractive materials among Tm-doped crystals due to their suitable characteristics, such as high values of absorption and stimulated emission cross sections, incignificant concentration quenching of luminescence, well-proven technology of the high quality crystals growth. The purpose of this paper was to compare lasing properties of lasers based on potassium lutetium and potassium yttrium tungstate crystals doped with thulium ions in continuous-wave regime. Experiments were carried out with a diode pumping in microchip cavity configuration. The maximum power of laser radiation at 1947 nm of 1010 mW was obtained with Tm:KY(WO4)2 crystal with the slope efficiency with respect to the absorbed pump power of 51 %. When Tm:KLu(WO4)2 crystal was utilized an output power of 910 mW at 1968 nm wavelength with the slope efficiency of 38 % was obtained. With Tm:KLu(WO4)2 laser a tuning range over 160 nm range was realized with a prism inserted into the laser cavity.
ОСОБЕННОСТИ ОБНАРУЖЕНИЯ ПОВЕРХНОСТНЫХ ДЕФЕКТОВ С ПОМОЩЬЮ ИМПУЛЬСНО-ЛАЗЕРНОГО ВОЗБУЖДЕНИЯ УПРУГИХ ВОЛН
Get PDFLaser pulse simulation of the surface waves and its receiving by contact piezoelectric probes is perspective direction to detect surface defects. The aim of this work was to determine optimal conditions for detection of the real fatigue cracks of nearly microns width and surface pores by moving depending on the position of the center of a laser beam laser beam spot. The objects of research were metal specimens with crack’s width of 8 m up to 0,5 mm and depth ≈ 400– 500 mm up to ≈ 200 mm. Cylindrical hole by ≈ 1 mm diameter used as a model pore. An experimental installation used consisted of the pulse laser light emission source with laser wavelength of 1.06 m and laser pulse duration of ≈ 20 ns. An arrangement to adjust the laser beam spot geometry in the form of a long strip and a circle was applied. Surface waves were received by the 2.7 MHz frequency probe, and processed with use of a «Spectronic» TDS 3052B oscilloscope. The laws of acoustical signal amplitude and its form changes vs. the laser beam spot geometry and its position in regard to defect were determined. We discovered that optimal conditions for flaw detection took place when the laser beam spot moving trough the defect’s range – crack and pore. In the first case amplitude growth of the signal was up to 7–8 time – like as resonance conditions realized. And the ratio of the laser’s beam spot width (as long strip) to wave length were ≈ 1.8–2.2. The more informative parameter to find crack with small width (≈ 0.5mm) was the acoustical pulse spectrum or the pulse entrance part. Thus, the further increasing of the surface flaw detection may be realized by laser simulation of the surface waves controlling the form of the moving spot of laser beam. New possibilities to increase sensitivity and reliability of ultrasonic evaluation surfaces in objects with complicated profile and fare accessible places are to be arise
ПОЛУЧЕНИЕ ИЗОБРАЖЕНИЯ ОБЪЕКТОВ ВО ВТОРИЧНЫХ РЕНТГЕНОВСКИХ ЛУЧАХ С ИСПОЛЬЗОВАНИЕМ ПИНХОЛ КАМЕРЫ
Get PDFPinhole camera is one of X-ray optics devices. The pinhole camera is used for obtaining the image of synchrotron and laboratory sources, and also as a lens in a method of X-ray fluorescent microscopy. This method allows to obtain information on a spatial distribution of various chemical elements to the areas of several square centimeters with spatial resolution at the level of 50–100 μm. As a rule energy-dispersive two-dimensional CCD cameras are used for imaging. Such cameras are expensive devices and have low sensitivity for X-rays with energy of photons higher than 8 keV. Therefore it is perspective to use for X-ray fluorescent microscopy more effective CCD cameras with a scintillator layer. The purpose of this work consists in development of the device for imaging with secondary fluorescent X-rays by using pinhole as a lens and CCD camera for registration of the X-ray image. The device for obtaining the image of objects in secondary X-rays is developed. The device consists of an X-ray tube, pinhole and CCD camera. The object of research was irradiated with radiation from the X-ray tube and emits secondary X-rays. 100-microns pinhole was used for formation of the image of the object at an entrance window of the CCD camera. Images of a number of the iron springs differing in the sizes are received. It is established that the spatial resolution of the device is about 200 μm at an exposition of 60 s. It is possible to improve permission of the device by increasing in an exposition, optimization imaging conditions and reduction of the pinhole size.
ФОРМИРОВАНИЕ ПОЛЯ ЗАХВАТНОГО ГАММА-ИЗЛУЧЕНИЯ ДО 10 МэВ ДЛЯ МЕТРОЛОГИЧЕСКОГО ОБЕСПЕЧЕНИЯ ПРИБОРОВ РАДИАЦИОННОЙ ЗАЩИТЫ
Get PDFMedical, and technological linear particle accelerators, and nuclear reactors are vastly widespread worldwide today. These facility generate fields of secondary gamma radiation with energy to 10 MeV. Therefore, we have a need to calibrate spectrometric and dosimetric ionization measurement instruments for the energies to 10 MeV. The aim of this work is to determine possibility to use thermal neutron collimator of АТ140 Neutron Calibration Facility with 238Pu-Be fast neutron source (IBN-8-6) for this. Below 3 MeV we use a set of point gamma standard spectrometry sources OSGI. We can acquire gamma rays with energies above 3 MeV using radioactive thermal neutron capture on target, i.e. (n, γ)-nuclear reaction. We can use neutron capture gamma-ray from titanium target (to 7 MeV) or nickel target (to 10 MeV) situated in thermal neutron field for calibration. We can use thermal neutron collimator of АТ140 Neutron Calibration Facility with 238Pu-Be fast neutron source (IBN-8-6) for slowing down neutrons from radionuclide fast neutron sources to thermal energies in polyethylene. Thermal neutron collimator forms a beam from radionuclide source with a significant amount of neutrons with thermal energies. We placed Ti and Ni targets in collimator’s canal. We got experimental spectral data on detection unit BDKG-19M NaI(Tl) 63 × 160 mm with nonlinear channel-energy conversion characteristic in range to 10 MeV. For additional filtration we proposed to use polyethylene neutron reflector and lead discs. We experimentally determined that placement of lead discs in collimator in front of the target allows to filter all spectrum while insignificantly weakening target’s emission. Using theoretical and experimental data we proved the ability to calibrate gamma-ray spectrometers in the range to 10 MeV.
МЕТОДИКА ОПРЕДЕЛЕНИЯ ОШИБКИ В ОПОРНОМ ЗНАЧЕНИИ ДОЗЫ ПРИ КАЛИБРОВКЕ РАДИАЦИОННОГО ВЫХОДА ЛИНЕЙНОГО УСКОРИТЕЛЯ. Часть 2. Зависимость от характеристик коллиматора, указателя расстояния источникповерхность, радиационного поля, лазерных центраторов, терапевтического стола
Get PDFМЕТОДИКА ОПРЕДЕЛЕНИЯ ОШИБКИ В ОПОРНОМ ЗНАЧЕНИИ ДОЗЫ ПРИ КАЛИБРОВКЕ РАДИАЦИОННОГО ВЫХОДА ЛИНЕЙНОГО УСКОРИТЕЛЯ. Часть 3. Зависимость от характеристик радиационного пучка
Get PDFTo ensure the radiation protection of oncology patients is needed to provide the constancy of functional characteristics of the medical linear accelerators, which affect the accuracy of dose delivery. For this purpose, their quality control procedures are realized including calibration of radiation output of the linac, so the error in determining the dose reference value during this procedure must not exceed 2 %. The aim is to develop a methodology for determining the error in determining this value, depending on the characteristics of the radiation beam. Dosimetric measurements of Trilogy S/N 3567 linac dose distributions have been carried out for achievement of the objectives, on the basis of which dose errors depending on the dose rate value, the accuracy of the beam quality and output factors determination, the symmetry and uniformity of the radiation field, the angular dependence of the linac radiation output were obtained. It was found that the greatest impact on the value of the error has the error in the output factors determination (up to 5.26 % for both photon energy). Dose errors caused by changing dose rate during treatment were different for two photon energies, and reached 1.6 % for 6 MeV and 1.4 % for 18 MeV. Dose errors caused by inaccuracies of the beam quality determination were different for two photon energies, and reached 1.1 % for 18 MeV and –0.3 % for 6 MeV. Errors caused by the remaining of the characteristic do not exceed 1 %. Thus, there is a possibility to express the results of periodic quality control of the linear accelerator in terms of dose and use them to conduct a comprehensive assessment of the possibility of clinical use of a linear accelerator for oncology patients irradiation on the basis of the calibration of radiation output