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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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Svařování elektronovým svazkem v ÚPT: Minulost a současnost
Zobač, Martin ; Vlček, Ivan
The paper deals with the history of an electron beam welding in the Institute of Scientifics Instruments in Brno, Czech republic. The description starts with the oldest technological e-beam device - multifunction vacuum furnace - dated from 1965, describes development of electron beam welders and introduces the newest instrument - Micro Electron Beam Welder MEBW-60/2, which was recently designed for German company Focus GmbH.
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Computations of Wien Filter Properties and Aberrations
Lencová, Bohumila ; Vlček, Ivan
Wien filter is studied in electron optics as a separator in a LEEM or as a separator of primary and secondary beams in a low voltage SEM. The advantage of the Wien filter is that one beam is only slightly influenced by the filter and the second beam can easily be handled, the required separation angle for this is about 10-20 degrees. The computation of aberrations of the Wien filter needs to take into account field shapes of both strong dipole fields and the additional quadrupole, the action of the filter is then that of a weak lens and the aberation structure is more complicated than that of a rotationally symmetric lens. The determination of aberation coefficients from direct ray tracing for this optical element is often preferred to aberration theory.
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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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