Browsing by Subject "radiation detectors"

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  • Brunbauer, Florian M.; Garcia, Francisco; Korkalainen, Tero; Lugstein, Alois; Lupberger, Michael; Oliveri, Eraldo; Dorothea, Dorothea; Ropelewski, Leszek; Thuiner, Patrik; Schinnerl, Markus (2018)
    Optically read out time projection chambers (TPCs) based on gaseous electron multipliers (GEMs) combine 3-D event reconstruction capabilities with high spatial resolution and charge amplification factors. The approach of reconstructing particle tracks from 2-D projections obtained with imaging sensors and depth information from photomultiplier tubes is limited to specific cases such as straight particle trajectories. A combination of optical and electronic readout realized by a semitransparent anode placed between a triple-GEM stack and a camera in an optically read out TPC has been realized and used to reconstruct more complex particle tracks. High spatial resolution 2-D projections combined with a low number of charge readout channels enable accurate 3-D event topology reconstruction. Straight alpha tracks as well as more complex cosmic events have been reconstructed with the presented readout concept. Relative depth information from electronically read out charge signals has been combined with drift time information between primary and secondary scintillation pulses to absolute alpha track reconstructions.
  • Naaranoja, Tiina; Golovleva, Maria; Gädda, Akiko; Martikainen, Laura; Ott, Jennifer; Berretti, Mirko; Garcia, Francisco; Luukka, Panja; Tuuva, Tuure; Österberg, Kenneth (2019)
    The radiation hardness of diamond at the sensor level is studied by irradiating five sensors and studying them with various particle sources, without making any modifications to the sensors in between. The electronics used in the characterization is not irradiated to ensure that any observed effect is merely due to the sensor. Three sensors have received a fluence of 10 (14) protons cm(-2) and two 5 center dot 10 (15) protons cm(-2). At the lower fluence, the impact on the charge collection efficiency is very small, when the applied bias voltage is above 1 V mu m(-1). For the higher fluence, the charge collection efficiency is lower than expected based on earlier studies of diamond radiation hardness on the substrate level. Furthermore, it is noticed that the irradiation has a stronger impact on the signal amplitude recorded with a fast timing than with a charge sensitive amplifier.
  • Rantanen, Milla-Maarit (Helsingin yliopisto, 2020)
    Semiconductor radiation detectors are devices used to detect electromagnetic and particle radiation. The signal formation is based on the transportation of charges between the valence band and conduction band. The interaction between the detector material and the radiation generates free electrons and holes that move in opposite directions in the electric field applied between the electrodes. The movement of charges induces a current in the external electrical circuit, which can be used for particle identification, measurement of energy or momentum, timing, or tracking. There are several different detector materials and designs and, new options are continuously developed. Diamond is a detector material that has received a great amount of interest in many fields. This is due to its many unique properties. Many of them arise from the diamond crystal structure and the strength of the bond between the carbon atoms. The tight and rigid structure makes diamond a strong and durable material, which allows operation of diamond detectors in harsh radiation environments. This, combined with the fast signal formation and short response time makes diamond detector an excellent choice for high energy physics applications. The diamond structure leads also to a wide band gap. Thanks to the wide band bap, diamond detectors have low leakage current and they can be operated even in high temperatures without protection from surrounding light. Especially electrical properties of semiconductors strongly depend on the concentration of impurities and crystal defects. Determination of electrical properties can therefore be used to study the crystal quality of the material. The electrical properties of the material determine the safe operational region of the device and knowledge of the leakage current and the charge carrier transportation mechanism are required for optimized operation of detectors. Characterization of electrical properties is therefore an important part of semiconductor device fabrication. Electrical characterization should be done at different stages of the fabrication in order to detect problems at an early stage and to get an idea of what could have caused them. This work describes the quality assurance process of single crystal CVD (chemical vapour deposition) diamond detectors for the PPS-detectors for the CMS-experiment. The quality assurance process includes visual inspection of the diamond surfaces and dimensions by optical and cross polarized light microscopy, and electrical characterization by measurement of leakage current and CCE (charge collection efficiency). The CCE measurement setup was improved with a stage controller, which allows automatic measurement of CCE in several positions on the diamond detector. The operation of the new setup and the reproducibility of the results were studied by repeated measurements of a reference diamond. The setup could successfully be used to measure CCE over the whole diamond surface. However, the measurement uncertainty is quite large. Further work is needed to reduce the measurement uncertainty and to determine the correlation between observed defects and the measured electrical properties.