51 research outputs found
Ion-induced effects in GEM & GEM/MHSP gaseous photomultipliers for the UV and the visible spectral range
We report on the progress in the study of cascaded GEM and GEM/MHSP gas
avalanche photomultipliers operating at atmospheric pressure, with CsI and
bialkali photocathodes. They have single-photon sensitivity, ns time resolution
and good localization properties. We summarize operational aspects and results,
with the highlight of a high-gain stable gated operation of a visible-light
device. Of particular importance are the results of a recent ion-backflow
reduction study in different cascaded multipliers, affecting the detector's
stability and the photocathode's liftime. We report on the significant progress
in ion-blocking and provide first results on bialkali-photocathode aging under
gas multiplication.Comment: 6 pages, 8 figure
Development of high gain GEM detectors
We describe systematic measurements carried out with single and double GEM detectors with printed circuit readout. The maximum safe operating gain has been measured at increasing radiation flux and under exposure to heavily ionizing tracks. Detection efficiency, localization accuracy and cluster size have been measured in a minimum ionizing particle beam. With a suitably configured readout electrode, fast, two-dimensional localization of radiation is demonstrated. (15 refs)
Further progress in ion back-flow reduction with patterned gaseous hole-multipliers
A new idea on electrostatic deviation and capture of back-drifting
avalanche-ions in cascaded gaseous hole-multipliers is presented. It involves a
flipped reversed-bias Micro-Hole & Strip Plate (F-R-MHSP) element, the strips
of which are facing the drift region of the multiplier. The ions, originating
from successive multiplication stages, are efficiently deviated and captured by
such electrode. Experimental results are provided comparing the ion-blocking
capability of the F-R-MHSP to that of the reversed-bias Micro-Hole & Strip
Plate (R-MHSP) and the Gas Electron Multiplier (GEM). Best ion-blocking results
in cascaded hole-multipliers were reached with a detector having the F-R-MHSP
as the first multiplication element. A three-element F-R-MHSP/GEM/MHSP cascaded
multiplier operated in atmospheric-pressure Ar/CH4 (95/5), at total gain of
~10^{5}, yielded ion back-flow fractions of 3*10^{-4} and 1.5*10^{-4}, at drift
fields of 0.5 and 0.2 kV/cm, respectively. We describe the F-R-MHSP concept and
the relevance of the obtained ion back-flow fractions to various applications;
further ideas are also discussed.Comment: 17 pages, 11 figures, published in JINS
Construction and Performance of a Micro-Pattern Stereo Detector with Two Gas Electron Multipliers
The construction of a micro-pattern gas detector of dimensions 40x10 cm**2 is
described. Two gas electron multiplier foils (GEM) provide the internal
amplification stages. A two-layer readout structure was used, manufactured in
the same technology as the GEM foils. The strips of each layer cross at an
effective crossing angle of 6.7 degrees and have a 406 um pitch. The
performance of the detector has been evaluated in a muon beam at CERN using a
silicon telescope as reference system. The position resolutions of two
orthogonal coordinates are measured to be 50 um and 1 mm, respectively. The
muon detection efficiency for two-dimensional space points reaches 96%.Comment: 21 pages, 17 figure
Development of high-gain gaseous photomultipliers for the visible spectral range
We summarize the development of visible-sensitive gaseous photomultipliers,
combining a semitransparent bi-alkali photocathode with a state-of-the-art
cascaded electron multiplier. The latter has high photoelectron collection
efficiency and a record ion blocking capability. We describe in details the
system and methods of photocathode production and characterization, their
coupling with the electron multiplier and the gaseous-photomultiplier operation
and characterization in a continuous mode. We present results on the properties
of laboratory-produced KCsSb, CsSb and NaKSb photocathodes and
report on their stability and QE in gas; KCsSb photocathodes yielded QE
values in Ar/CH(95/5) above 30% at wavelengths of 360-400 nm. The novel
gaseous photomultiplier yielded stable operation at gains of 10, in
continuous operation mode, in 700 Torr of this gas; its sensitivity to single
photons was demonstrated. Other properties are described. The successful
detection of visible light with this gas-photomultiplier pave ways towards
further development of large-area sealed imaging detectors, of flat geometry,
insensitive to magnetic fields, which might have significant impact on light
detection in numerous fields.Comment: 22 pages, 12 figures, for submission to JINS
Single-UV-photon 2-D imaging with multi-GEM detectors
The main goal being the construction of large-area, low-cost position-sensitive micropattern gaseous photomultipliers (GPMs) based on gas electron multipliers (GEM) cascades, we have studied the single-photon imaging capabilities of a 4-GEM GPM with a reflective CsI-photocathode deposited on the top surface of the 1st GEM. The charge readout was performed with a simple/economic Wedge and Strip (W&S) readout electrode, using pulses induced through a resistive electrode. We have demonstrated the feasibility of single-photon imaging GPM with sub-millimeter resolution; single-photon spatial resolutions as small as ~150Ă‚Â [mu]m (FWHM), i.e. ~65Ă‚Â [mu]m (RMS), were measured in Ar/5%CH4 gas mixture at atmospheric pressure.http://www.sciencedirect.com/science/article/B6TJM-4NS2G9V-M/1/b808ebe094732f4310ee7686c9118a7
Advances in the Micro-Hole & Strip Plate gaseous detector
We report on the performance of a new gaseous electron multiplier: the Micro-Hole & Strip Plate (MHSP). It consists of two independent charge-amplification stages in a single, double-sided micro-structured electrode, deposited on a thin insulating substrate. Charge gains in excess of 103 were obtained in a MHSP operated with soft X-rays in Ar/CO2 (70/30). We present the results of a systematic study of the MHSP properties and those of a double-stage GEM+MHSP multiplier. Applications to gaseous photomultipliers are discussed.http://www.sciencedirect.com/science/article/B6TJM-48GF7W8-1/1/9ca82a7819a2c55a59c29ed0a8803a9
Two-dimensional readout of GEM detectors
The recently introduced Gas Electron Multiplier (GEM) permits the amplification of electrons released by ionizing radiation in a gas by factors approaching ten thousand, larger gains can be obtained combining two GEMs in cascade. We describe methods for implementing two- and three-dimensional projective localization of radiation, with sub-millimeter accuracy, making use of specially manufactured and patterned pick-up electrodes. Easy to implement and flexible in the choice of the readout geometry, the technology has the distinctive advantage of allowing all pick-up electrodes to be kept at ground potential, thus substantially improving the system simplicity and reliability. Preliminary results demonstrating the two-dimensional imaging capability of the devices are provided and discussed, as well as future perspectives of development
Blood flow changes using a 3D xenogeneic collagen matrix or a subepithelial connective tissue graft for root coverage procedures: a pilot study.
BACKGROUND: The study investigated the early healing process following the treatment of single Miller class I and II recessions with a 3D xenogeneic collagen matrix (CMX) or connective tissue graft (CTG). METHODS: This pilot investigation was designed as a single-center randomized controlled parallel trial. A total of eight subjects (four per group) were treated with either CMX or CTG in the anterior maxilla. Vascular flow changes were assessed by laser Doppler flowmetry (LDF) before and after surgery and at days 1, 2, 3, 7, 14, and 30 while clinical evaluations took place at baseline and at days 60 and 180. Pain intensity perception was evaluated by the short-form McGill pain questionnaire (SF-MPQ), at days 1 and 14. RESULTS: The vascular flow fluctuated similarly in both groups pre- and post-operatively, but the CTG exhibited a more homogeneous pattern as opposed to CMX that showed a second phase of increased blood flow at 14Â days. Clinically, the CTG led to greater change in mean root coverage and keratinized tissue gain but CMX was associated with lower early pain intensity scores. CONCLUSIONS: Within the limits of the study, the vascular flow alterations during the early healing of both graft types followed a similar pattern. The CMX was associated with a second peak of increased blood flow. CLINICAL RELEVANCE: The vascular flow changes after the application of CMX for single tooth recession root coverage did not show major differences from those observed after the use of a CTG. A trend for better clinical performance in terms of root coverage and keratinized tissue gain was noted for the CTG, but the initial patient morbidity was less for CMX
PRELIMINARY REPORT ON THE PUTATIVE ASSOCIATION OF IL10 -3575 T/A GENETIC POLYMORPHISM WITH MALARIA SYMPTOMS
Only a small percentage of individuals living in endemic areas develop severe malaria suggesting that host genetic factors may play a key role. This study has determined the frequency of single nucleotide polymorphisms (SNPs) in some pro and anti-inflammatory cytokine gene sequences: IL6 (-174; rs1800795), IL12p40 (+1188; rs3212227), IL4 (+33; rs2070874), IL10 (-3575; rs1800890) and TGFb1 (+869; rs1800470), by means of PCR-RFLP. Blood samples were collected from 104 symptomatic and 37 asymptomatic subjects. Laboratory diagnosis was assessed by the thick blood smear test and nested-PCR. No association was found between IL6 (-174), IL12p40 (+1188), IL4 (+33), IL10 (- 3575), TGFb1 (+869) SNPs and malaria symptoms. However, regarding the IL10 -3575 T/A SNP, there were significantly more AA and AT subjects, carrying the polymorphic allele A, in the symptomatic group (c2 = 4.54, p = 0.01, OR = 0.40 [95% CI - 0.17- 0.94]). When the analysis was performed by allele, the frequency of the polymorphic allele A was also significantly higher in the symptomatic group (c2 = 4.50, p = 0.01, OR = 0.45 [95% CI - 0.21-0.95]). In conclusion, this study has suggested the possibility that the IL10 - 3575 T/A SNP might be associated with the presence and maintenance of malaria symptoms in individuals living in endemic areas. Taking into account that this polymorphism is related to decreased IL10 production, a possible role of this SNP in the pathophysiology of malaria is also suggested, but replication studies with a higher number of patients and evaluation of IL10 levels are needed for confirmation
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