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Coincidence imaging System with Electron Optics
Kroupa, M. ; Jakoubek, J. ; Krejčí, E. ; Valach, O. ; Horáček, Miroslav ; Radlička, Tomáš ; Vlček, Ivan
Instrumental neutron activation analysis (INAA) is a widely used method for elemental analysis. After the sample is put into a neutron field, where nuclei of interest become activated, these nuclei emit gamma photons with characteristic energies for each element. By measuring gamma spectrum of the activated sample one can determine the sample elemental composition with very high precision. In order to find out the spatial distribution of elements, the sample is usually cut into pieces, which are examined individually. Such procedure is time consuming and the spatial resolution is limited by the size of the pieces. This contribution follows up the work where the semiconductor pixel detector Timepix was used for revealing the concentration and distribution of certain elements in a whole sample at once (imaging coincidence INAA) [1]. Photons detected by a standard semiconductor detector were used to trigger the Timepix device which detected the accompanying electrons.
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Měření elektronově-optických vlastností Wienova filtru stínovou metodou
Horáček, Miroslav ; Vlček, Ivan ; Zobač, Martin
Wien filter is suitable for the separation of the primary and the signal electron beams in very low energy scanning electron microscope with cathode lens. We have modified the two-grid shadow method to determine experimentally electron optical properties (cardinal elements and aberrations) of the Wien filter, which is not a rotationally symmetric element. We call the modified method the shadow method with grid and moving screen. The advantage of the shadow method is its geometrical simplicity allowing the comparison of the experimentally obtained and numerically computed trajectories.
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Detective quantum efficiency of electron bombarded CCD
Horáček, Miroslav
Detective quantum efficiency (DQE) describes the ability of the image sensor to transfer input image information into the output electrical signal from the point of view of added noise. DQE was measured in direct electron bombarded mode using an empty image and the mixing facor method for energies of electrons 2 to 5 keV. DQE increases with increasing energy of bombarded electrons. Optimum wotking energy from the point of view of dynamic range, brightness resolutin, and integration time of the sensor is 4.2 keV. DQE is 0.7 for this energy and integration time below 10 ms.
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Temperature controlled cathode heating in the electron gun
Horáček, Miroslav
The paper describes how the lifetime of the directly heated tungsten cathode can be substantially extended by automatic stabilisation of its temperature measured by its luminance. Further it is shown that the end of the life (the break) of the cathode can be predicted, giving the operating personnel the chance to avoid unexpected break during the experiment.
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Detection of angular distribution of the signal electrons in VLESEM
Horáček, Miroslav
The aim of this work is to design a detector for the angle and energy-selective detection of signal electrons in very low energy scanning electron microscopy (VLESEM), based on the directly electron-bombarded CCD sensor (EBCCD). The planar CCD sensor is very suitable for conversion of the area information carried by impinging electrons of the signal beam into the electrical signal that can be further processed.
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Návrh nízkoenergiového REM
Vlček, Ivan ; Lencová, Bohumila ; Horáček, Miroslav
Our aim is to redesign the low-energy SEM (a scanning LEEM) in an UHV apparatus designed in our institute to allow the detection of the angular distribution of signal electrons. For this purpose we have to separate the signal electrons from the primary beam with a Wien filter and project the image of the back-focal plane of the objective lens on an area-sensitive detector (a back-illuminated CCD). Therefore we have to design a new electrostatic optics working in UHV
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