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| 3. |
- Davidsson, D. W., et al.
(författare)
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Limitations to flat-field correction methods when using an X-ray spectrum
- 2003
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; , s. 146-150
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Tidskriftsartikel (refereegranskat)abstract
- Flat-field correction methods are implemented in order to eliminate non-uniformities in X-ray imaging sensors. If the compensation is perfect, then the remaining variations result from noise over the detector area. The efficiency of the compensation is reduced when an object is placed in the beam. A principle cause of this effect is believed to be the spectrum hardening caused by the object. In a normal application the correction factors are calculated for a certain spectrum, meaning that the average of the correction for the individual photon energies are used. If the composition of the spectrum changes the correction factor will also change. In this paper, we present a theory for the sensitivity of the gain constants on X-ray spectra. The theory is supported by experimental data obtained with X-ray spectra and monochromatic X-rays.
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| 4. |
- Dubaric, Ervin, et al.
(författare)
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Monte Carlo simulation of the response of a pixellated 3D photodetector in silicon
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 487:1-2, s. 136-141
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Tidskriftsartikel (refereegranskat)abstract
- The charge transport and X-ray photon absorption in three-dimensional (3D) X-ray pixel detectors have been studied using numerical simulations. The charge transport has been modelled using the drift-diffusion simulator MEDICI, while photon absorption has been studied using MCNP. The response of the entire pixel detector system in terms of charge sharing, line spread function and modulation transfer function, has been simulated using a system level Monte Carlo simulation approach. A major part of the study is devoted to the effect of charge sharing on the energy resolution in 3D-pixel detectors. The 3D configuration was found to suppress charge sharing much better than conventional planar detectors.
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| 5. |
- Dubaric, Ervin, et al.
(författare)
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Monte Carlo simulations of the imaging properties of scintillator coated X-ray pixel detectors
- 2000
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Ingår i: IEEE Nuclear Science Symposium and Medical Imaging Conference. - : IEEE conference proceedings. - 0780365038 ; , s. 6/282-6/285
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Konferensbidrag (refereegranskat)abstract
- The imaging properties of X-ray pixel detectors depend on the quantum efficiency for X-rays, the generated signal for each X-ray photon and the distribution of the generated signal between different pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. Hence, the signal-to-noise ratio (SNR) in the image is then a function of the number of photons captured in each of these processes, and the yield of each process, in terms of electron-hole pairs (EHPs) produced in the semiconductor. The full process from the absorption of the X-ray photon to the final signal read out from the detector has been simulated with a combination of the Monte Carlo program MCNP and the commercial carrier transport simulation tool MEDICI. An in house program calculating the light transport between the scintillator and the semiconductor serves as a link
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| 6. |
- Dubaric, Ervin, et al.
(författare)
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Resolution and noise properties of scintillator coated X-ray detectors
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 178-182
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Tidskriftsartikel (refereegranskat)abstract
- The imaging properties of X-ray pixel detectors depend on the quantum efficiency of X-rays, the generated signal of each X-ray photon and the distribution of the generated signal between pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. The Signal-to-Noise Ratio in the image is then a function of the number of photons captured in each of these processes and the yield, in terms of electron-hole pairs produced in the semiconductor, of each process. The spatial resolution is primarily determined by the light spreading within the scintillator. In a pure semiconductor detector the signal is generated by one process only. The Signal-to-Noise Ratio in the image is proportional to the number of X-ray photons captured within the sensitive layer. The spatial resolution is affected by the initial charge cloud generated in the semiconductor and any diffusion of carriers between the point of interaction and the readout electrode. In this paper we discuss the theory underlying the imaging properties of scintillator coated X-ray imaging detectors. The model is verified by simulations using MCNP and by experimental results. The results from the two-layer detector are compared with those from a pure semiconductor X-ray detector.
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| 7. |
- Fröjdh, Christer, et al.
(författare)
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Characterization of a pixellated CdTe detector with single-photon processing readout
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 563:563, s. 128-132
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Tidskriftsartikel (refereegranskat)abstract
- A 1mm thick pixellated CdTe detector bonded to the MEDIPIX2 [1] readout chip has been characterized using a monoenergetic microbeam at the ESRF. This is an extension of the tests previously reported in [2]. The results show that a full energy peak can be obtained when a narrow beam is focused in the centre of the pixel. There is also evidence of significant charge diffusion and fluorescence. The results indicate that the charge sharing is the most important problem and will cause loss of the energy information in an imaging application. The second problem is the fluorescence which limits the number of counts in the full energy peak even for hits in the centre of the pixel.
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| 8. |
- Fröjdh, Christer, et al.
(författare)
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Processing and characterisation of an etched groove Permeable
- 1994
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Ingår i: Physica scripta. T. - 0281-1847. ; T54, s. 56-59
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Tidskriftsartikel (refereegranskat)abstract
- The Permeable Base Transistor (PBT) is generally considered as an interesting device for high speed applications. PBTs have been fabricated on Silicon and Gallium Arsenide by a number of groups. In this paper we reported on the fabrication of an etched groove PBT structure on 6H-SiC using Ti as contact metal for all electrodes. The devices have been characterised by DC-measurements. The transistors show the normal IV-characteristics for a such a device except for a parasitic series diode at the drain electrode. The breakdown voltage of the gate-drain diode is generally as high as around 60 V even without passivation of the sidewalls of the grooves.
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| 9. |
- Fröjdh, Christer, et al.
(författare)
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Schottky Barriers on 6H-SiC
- 1999
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Ingår i: Physica scripta. T. - 0281-1847. ; T79, s. 297-302
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Tidskriftsartikel (refereegranskat)abstract
- Schottky diodes have been fabricated by deposition of Ti, Ni, Cu on epitaxial layers of p-type and n-type 6H-SiC. The fabricated devices have been characterised by CV, IV and photoelectric measurements. The results from the different characterisations are compared. The effect of incomplete ionisation of dopants and high series resistance on the results from CV-measurements is discussed. In addition to the results obtained from the experiments presented in this paper data has also been collected from other research groups in order to investigate the mechanism of Schottky barrier formation on Silicon Carbide. The results show that for a number of metals the barrier height is strongly correlated to the difference between the electron affinity of the semiconductor and the metal work function, while other metals show significant deviation from the Schottky-Mott theory.
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