C. A. Santos

Ion backflow in thick GEM-based detectors of single photons

Photon detectors based on micropattern gas detectors represent a new generation of gaseous photon detectors. In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we are performing an R&D programme aimed both to establish the principles and to develop the engineering aspects of photon detectors based on multi-layer arrangements of thick GEMs electron multipliers coupled to a CsI photoconverter. In this context, a reduced rate of the backflow of the positive ions generated in the multiplication process is required to overcome the critical issues related to the bombardment of the CsI photoconverter by ions. Our studies devoted to develop detector architectures able to provide reduced ion backflow rates are reported.

Progresses in the production of large-size THGEM boards

The THicK GEM (THGEM) electron multipliers are derived from the GEM design, by scaling the geometrical parameters and changing the production technology. Small-size (a few cm2) detectors exhibit superb performance, while larger ones exhibit gain response and uniformity limitations. We have studied with a systematic approach several aspects concerning the material (type and thickness of the fibreglass plates) and the production procedure, in particular the cleaning and polishing stages. The net result is the production of large THGEM multipliers reproducing the performance of the small ones. We report in detail about the studies and the results.

The gain in Thick GEM multipliers and its time-evolution

In the context of a project to upgrade the gas photon detectors of COMPASS RICH-1, we have performed an R&D programme aimed to develop photon detectors based on multi-layer arrangements of thick GEM electron multipliers coupled to a CsI photoconverter. For this purpose, thick GEMs have been characterised in detail including the gain performance, its dependance on the geometrical parameters and its time-evolution, a feature exhibited by the gas detectors with open insulator surfaces. The variation due to this evolution drammatically depends on the parameters themselves. In the present article we summarise the outcomes of the studies dedicated to the thick GEM gain and its evolution versus time. We also include a qualitative model which accounts for the peculiar details of the observed thick GEM gain time-evolution.

Energy weighting in a 2D-MHSP x-ray single photon detector

The 2D-MicroHole and Strip Plate (MHSP) is a simple single photon counting detector for x-ray imaging. It is a micropattern gas detector having two orthogonal resistive lines crossing the amplification and readout electrodes on both sides of the MHSP for position detection. In this detector, not only the interaction position point can be determined, but also the energy of individual photons. The detector energy resolving capability offers the possibility of obtaining three types of images: Integrating, Counting and Energy Weighting. The intensity of each pixel is obtained by adding the energy of each event, at the first case, by counting the number of events in the second one, or by adding each event weighted by a factor that depends on its energy, at the third case. Preliminary results show a Contrast Enhancement up to 6% when Counting and Integrating images are compared and up to 20% when comparing Energy Weighting and Integrating images. For the present studies, a PVC step phantom is irradiated with a 20kV copper anode x-ray tube. A enhancement study of the Contrast and image quality between different techniques as a function of energy windows will be presented.

Status and progress of novel photon detectors based on THGEM and hybrid MPGD architectures

Recent progress in the development of THGEM-based photon detectors confirm the validity of this novel technology. Detectors made of THGEMs, arranged in a three layer architecture, with a CsI coating on the first layer (acting as a reflective photocathode), have been produced and operated in laboratory and during test beam runs: they provide a gain of 105 and a time resolution better than 10 ns. Improvements in the production of THGEMs with 300 ? 300 mm2 active area have recently been introduced leading to a uniform gain response and performance similar to that provided by the small area THGEMs. Promising results have been obtained by combining THGEM and Micromegas technologies to form a hybrid MPGD-based photon detector: the first prototype has proved to stably operate at large gain in a variety of gas mixtures, including pure CH4 and to provide a low ion backflow rate. The RICH-1 detector of the COMPASS Experiment at CERN SPS will be equipped with a set of MPGD-based photon detectors replacing MWPC-based ones.

Long term experience and performance of COMPASS RICH-1

COMPASS RICH-1 is a large size gaseous Imaging Cherenkov Detector providing hadron identification in the range from 3 to 55 GeV/c, in the wide acceptance spectrometer of the COMPASS Experiment at CERN SPS. It uses a 3 m long C4F10 radiator, a 21 m2 large VUV mirror surface and two kinds of photon detectors: MAPMTs and MWPCs with CsI photocathodes, covering a total of 5.5 m2. It is in operation since 2002 and its performance increased thanks to progressive optimization and to a major upgrade of its photon detection system, implemented in 2006; a new upgrade is foreseen for 2016, with the use of MPGD-based photon detectors. The main characteristics of COMPASS RICH-1 components are described and the most critical aspects related to the C4F10 radiator gas system, to the mirrors and their alignment, as well as the performance of the photon detectors are presented and discussed. The response of the MWPCs and the observed evolution of the effective quantum efficiency of the CsI photocathodes is analyzed. The properties and performance of the MAPMTs with individual fused lens telescopes are presented together with the readout characteristics. The PID performance of COMPASS RICH-1 is discussed and the future upgrade program is mentioned.

MPGD-based counters of single photons developed for COMPASS RICH-1

In fundamental research, gas detectors of single photons are a must in the field of Cherenkov imaging techniques (RICH counters) for particle identification in large momentum ranges and with wide coverage of the phase space domain. These counters, already extensively used, are foreseen in the setups of future experiments in a large variety of fields in nuclear and particle physics. The quest of novel gaseous photon detector is dictated by the fact that the present generation of detectors has unique characteristics concerning operation in magnetic field, low material budget and cost, but it suffers of severe limitations in effective efficiency, rates, life time and stability, discouraging their use in high precision and high rate experiments. We are developing large size THick GEM (THGEM)-based detector of single photons. The RD relevant progress in the engineering aspects, in particular related to the production of large-size THGEMs, where the strict correlation between the local gain-value and the local thickness-value has been demonstrated the operation of a 300 mm × 300 mm2 active area detector at the CERN PS T10 test beam; the introduction of a new hybrid detector architecture offering promising indication, which is formed by a THGEM layer which acts as CsI support and pre-amplification device followed by a MICROMEGAS multiplication stage. The general status of the R&D program and the recent progress are reported

Energy Weighting in a 2D-MHSP X-Ray Single Photon Detector

The 2D-MicroHole and Strip Plate (MHSP) is a simple single photon counting detector for X-ray imaging. It is a micropattern gaseous detector having two orthogonal resistive lines crossing the amplification and readout electrodes on both sides of the MHSP for position detection. In this detector, not only the interaction position can be determined, but also the energy of individual photons. The detector energy resolving capability offers the possibility of obtaining three types of images of the intensity distribution: Integrating, Counting and Energy Weighting. In the first case, the intensity of each pixel is obtained by adding the energy of each event; in the second case, by counting the number of events and; in the third case, by adding each event weighted by a factor that depends on its energy. When a PVC step phantom is irradiated with a 20 kV copper anode X-ray tube, the results show a Contrast Enhancement up to 6% when Counting and Integrating images are compared and up to 20% when comparing Energy Weighting and Integrating images. A biological sample, a common quail wing, was also imaged. Studies of the Contrast Enhancement and image quality between different techniques as a function of energy windows are present.

Pulmonary Rehabilitation in COPD: Effect of 2 Aerobic Exercise Intensities on Subject-Centered Outcomes—A Randomized Controlled Trial

BACKGROUND: Exercise training is an important component of pulmonary rehabilitation, but it remains questionable how training intensity affects patient-centered outcomes. The aim of this study was to compare the effects of 2 aerobic training intensities on health-related quality of life (HRQOL), symptom control, and exercise tolerance in subjects with COPD. METHODS: Thirty-four subjects with mild to very severe COPD participated in an equivalence/non-inferiority randomized controlled trial with a parallel group blinded to 60 or 80% maximum work rate (Wmax) aerobic training intensity. The intervention was an out-patient pulmonary rehabilitation program conducted 3 times/week for 8 weeks. Outcomes were assessed with the St George Respiratory Questionnaire (primary outcome), Mahlers dyspnea index, London Chest Activity of Daily Living scale, 6-min walk test, and constant-load and incremental exercise tests. RESULTS: Subjects were randomly allocated to aerobic training intensity of 60% Wmax (group 1, n = 17) or 80% Wmax (group 2, n = 17). Although there were significant improvements in all outcomes for both groups, there were no between-group differences in mean change in the St George Respiratory Questionnaire (P = .31, 95% CI −12.0 to 3.9), Mahlers dyspnea index (P = .38), London Chest Activity of Daily Living scale (P = .92), 6-min walk test (P = .50, 95% CI 6.2–71.1), constant-load exercise test (P = .50), and incremental exercise test (P = .12). There was only one exercise-related adverse event of cardiac symptoms. CONCLUSIONS: Aerobic training intensity of at least 60% Wmax has a positive impact on COPD patient-centered outcomes, with no additional benefit of increasing intensity to 80% Wmax in HRQOL, symptom control, and exercise tolerance, challenging the present clinical attitude of rehabilitation professionals. (ClinicalTrials.gov registration NCT01944072.)

Status of COMPASS RICH-1 Upgrade with MPGD-based Photon Detectors

A Set of new MPGD-based Photon Detectors is being built for the upgrade of COMPASS RICH-1. The detectors cover a total active area of 1.4 m 2 and are based on a hybrid architecture consisting of two THGEM layers and a Micromegas. A CsI film on one THGEM acts as a reflective photocathode. The characteristics of the detector, the production of the components and their validation tests are described in detail.