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| 2. |
- Iacobaeus, C., et al.
(författare)
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Sporadic electron jets from cathodes - The main breakdown-triggering mechanism in gaseous detectors
- 2002
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Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 49:4, s. 1622-1628
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Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated experimentally that the main breakdown-triggering mechanism in most gaseous detectors, including micropattern gaseous detectors, is sporadic electron jets from the cathode surfaces. Depending on the counting rate and applied voltages, each jet contains randomly from a few primary electrons up to 10(5), emitted in a time interval ranging between 0.1 mus to milliseconds. After the emission, these primary electrons experience a full gas multiplication in the detector and create spurious pulses. The rate of these jets increases with applied voltage and very sharply at voltages close to the breakdown limit. In our measurements, we found that these jets are responsible for the breakdown-triggering at any counting rate between 10(-2) Hz/mm(2) and 10(8) Hz/mm(2). We demonstrated on a few detectors that an optimized cathode-geometry, a high electrode surface quality, and a proper choice of the gas mixture considerably improve the performance characteristics and provide the highest possible gains. Results from this work were helpful in the construction of high-performance gaseous detectors for medical imaging applications.
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| 3. |
- Peskov, V., et al.
(författare)
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The study and optimization of new micropattern gaseous detectors for high-rate applications
- 2001
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 48:4, s. 1070-1074
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Tidskriftsartikel (refereegranskat)abstract
- We performed a new series of systematic studies of gain and rate characteristics of several micropattern gaseous detectors. Extending earlier studies, characteristics were measured at various pressures and gas mixtures at a wide range of primary charges, and also when the whole area of the detectors was irradiated with a high-intensity X-ray beam. Several new effects were discovered, common to all tested detectors, which define fundamental limits of operation. The results of these studies allow us to identify several concrete ways of improving the performance of micropattern detectors and to suggest that in some applications, resistive plate chambers may constitute a valid alternative. Being protected from damaging discharges by the resistive electrodes, these detectors feature high gain, high rate capability (10(5) Hz/mm(2)), good position resolution (better than 30 mum), and excellent timing (50 ps sigma).
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| 4. |
- Wallmark, M., et al.
(författare)
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Operating range of a gas electron multiplier for portal imaging
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 471:02-jan, s. 151-155
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Tidskriftsartikel (refereegranskat)abstract
- At the Karolinska Institute in Stockholm, Sweden a new detector for portal imaging is under development, which could greatly improve the alignment of the radiation beam with respect to the tumor during radiation treatment. The detector is based on solid converters combined with gas electron multipliers (GEMs) as an amplification structure. The detector has a large area and will be operated in a very high rate environment in the presence of heavy ionizing particles. As was discovered recently high rates and alpha particles could cause discharges in GEM and discharge propagation from GEM to GEM and to the readout electronics. Since reliability is one of the main requirements for the portal imaging device, we performed systematic studies to find a safe operating range of the device, free from typical high rate problems, such as discharges.
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