| 1. |
- Blanco, A, et al.
(author)
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Progress in timing Resistive Plate Chambers
- 2004
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 535:1-2, s. 272-276
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Journal article (peer-reviewed)abstract
- Timing RPCs are Resistive Plate Chambers made with glass and metal electrodes separated by precision spacers. Typical gas gaps are a few hundred micrometers wide. Such counters were introduced in 1999 and have since reached timing accuracies below 50 ps sigma with efficiencies above 99% for MIPs. Applications in high-energy physics have already taken place with several more under study. Some recent developments include the extension of the counting rate capability by over one order of magnitude, to 25 kHz/cm(2), with time resolutions below 100 ps sigma. A prototype RPC-based Positron Emission Tomograph yielded a reconstructed point-source resolution of 0.6 mm FWHM and a modified timing RPC design, featuring 50 mum pitch anode strips, allowed to reach extremely good position resolution for hard X-rays in digital readout mode. An analytically solvable model has allowed us to clarify the basic factors influencing the time resolution.
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| 2. |
- Danielsson, Mats, et al.
(author)
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Novel gaseous detectors for medical imaging
- 2004
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 518:1-2, s. 406-410
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Journal article (peer-reviewed)abstract
- We have developed and successfully tested prototypes of two new types of gaseous detectors for medical imaging purposes. The first one is called the Electronic Portal Imaging Device (EPID). It is oriented on monitoring and the precise alignment of the therapeutic cancer treatment beam (pulsed gamma radiation) with respect to the patient's tumor position. The latest will be determined from an X-ray image of the patient obtained in the time intervals between the gamma pulses. The detector is based on a sandwich of hole-type gaseous detectors (GEM and glass microcapillary plates) with metallic gamma and X-ray converters coated with CsI layers. The second detector is an X-ray image scanner oriented on mammography and other radiographic applications. It is based on specially developed by us high rate RPCs that are able to operate at rates of 10(5) HZ/mm(2) with a position resolution better than 50 mum at 1 atm. The quality of the images obtained with the latest version of this device were in most cases more superior than those obtained from commercially available detectors.
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| 3. |
- Francke, T, et al.
(author)
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High rate (up to 10(5) Hz/cm(2)), high position resolution (30 mu m) photosensitive RPCs
- 2004
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 533:1-2, s. 163-168
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Journal article (peer-reviewed)abstract
- In many applications there is a need for high position resolution VUV and UV imagers. For these applications we have developed and successfully tested 1D and 2D VUV imaging detectors based on microgap RPCs. Two versions of these detectors were extensively tested: one filled with photosensitive vapours and the other one with the GaAs cathode coated by a 400 nm thick CsI layer. The main feature of these detectors is the high position resolution-30 mum in digital form. Additionally, it is spark-protected and can operate at high counting rates (up to 10(5) Hz/cm(2)). In this study the results in application for these detectors for spectroscopy are presented.
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| 4. |
- Iacobaeus, C., et al.
(author)
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Sporadic electron jets from cathodes - The main breakdown-triggering mechanism in gaseous detectors
- 2002
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In: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 49:4, s. 1622-1628
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Journal article (peer-reviewed)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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| 5. |
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| 6. |
- Lopes, L, et al.
(author)
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Development of high-rate timing RPCs
- 2004
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 533:1-2, s. 69-73
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Journal article (peer-reviewed)abstract
- For many applications of RPCs to time-of-flight counters in heavy ion experiments the expansion to much higher values of the counting rate capability, so far limited to around 2 kHz/cm(2) is of fundamental importance. To address this issue we developed single-gap timing RPCs with resistive electrodes made from a commercially available plastic material. Tests performed in photon beams yielded a time resolution around 90 ps sigma, essentially unchanged from 2 kHz/ cm(2) to 27 kHZ/cm(2). This result establishes the basic feasibility of timing measurements with RPCs at rates of tens of kHZ/cm(2), keeping a time resolution below 100 ps a and using plastic electrode materials.
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| 7. |
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| 8. |
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| 9. |
- Peskov, V., et al.
(author)
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The study and optimization of new micropattern gaseous detectors for high-rate applications
- 2001
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In: 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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Journal article (peer-reviewed)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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| 10. |
- Wallmark, M., et al.
(author)
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Operating range of a gas electron multiplier for portal imaging
- 2001
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In: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 471:02-jan, s. 151-155
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Journal article (peer-reviewed)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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