جستجوی مقالات مرتبط با کلیدواژه "آشکارساز" در نشریات گروه "فیزیک"

X-ray applications in imaging and beyond require efficient and optimal detectors. Energy separation, time loss, and manufacturing cost are among the features that led us to design a semiconductor detector. A low-gain avalanche diode (LGAD) with internal amplification allows, in a sufficient field, the internal propagation process by accelerating the carriers, the energy required for ionization, and the generation of secondary carriers to produce a better gain (higher signal-to-noise ratio) and also provide more time efficiency (in the range of nanoseconds). In this article, we simulate the LGAD silicon detector with Silvaco software by applying reverse bias voltage and radiation in the range of visible light to X-ray. Newton and Gummel's methods were used. In Newton's method, one of the mechanisms of radiation interaction with matter is considered variable and the rest are fixed. However, in Gummel's method, all mechanisms are solved simultaneously. In the X-ray wavelength range, the electron current in this detector is 10-4 amperes, and this current decreases with increasing energy. The dark current is 10-6 amperes. By applying visible light with 0.45-micrometer wavelength and 1 V/cm2 intensity, the detector current was obtained about 6.5×10-4 amperes. For 1.0×10-5 x-ray wavelength and 108 V/cm2 intensity, detector current was obtained about 3.5×10-4 amperes. Considering the quick response time of this detector and the current in the range of microamps, this detector is a suitable option for X-ray detection. Also, this detector shows superior performance in the visible light range.

Alpha particles emit electromagnetic radiation as they stop in the environment due to ionization and exciting atoms. The energy spectrum and intensity of radiation depends on the material and the percentage of elements in the target and its thickness. By placing layers of different metals and materials and changing their thickness in front of the entrance window of CsI (Tl) scintillator and interpreting the change in intensity in different detector channels, a suitable method for detecting alpha particles is introduced. In this research, the alpha particles of 241Am source with an energy of 5.48 MeV are irradiated into layers of aluminum, copper, iron, steel, paper, radiological films, lead and plastic with different thicknesses and was studied the count  variation of CsI (Tl) scintillation channels. By interpreting the results, was obtained the channels that show the maximum intensity of photons due alpha particles stopping in target. According to the observation of X-ray channels related to alpha particle stopping in target, a method for radon detection has also been introduced. In this method, hot spring water is poured into a plastic container with a thin layer of iron embedded at the end. First the background spectrum was measured. Then the water inside the container is stirred and the difference in spectrum is measured. The most suitable channel for measuring radon is channel 57. According to the obtained results, the relationship between radon concentration and counting rate in this channel has been extracted.

In this paper, digital signal processing for precise gamma ray spectroscopy is presented. The basis of this system is a 14bit waveform digitizer which samples the output of pre-amplifier signals directly. The advantages and limitations of the digital spectrometer compared with analog spectrometer has been tested and analyzed from precise gamma ray spectroscopy point of view. The results shows that the digital pulse processing provides better energy resolution, longer stability in time, better peak to Compton ratio, higher throughput and effective elimination of ballistic deficit.

In studying the ultraviolet (UV) radiation, one of the important factors is the possibility of generating a variety of free radicals inside the body by these radiations. In this paper, a method of estimating the amount of hydroxyl radicals produced by ultraviolet rays was investigated using nanoparticles of tin oxide doped with uropium. In this method, the change in absorption intensity of methylene blue was used as a free radical detector. SnO2:Eu nanoparticles were synthesized using co-precipitation method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The changes in the intensity of the methylene blue absorption curve were investigated and it was found that this intensity decreases in the presence of nanoparticles, which indicates the formation of free radicals in ultraviolet radiation. Using the results of this method, it is possible to measure the amount of received ultraviolet radiation dose.