F. Murtas

Performance of a triple-GEM detector for high rate charged particle triggering

We report the results of a systematic study of the performance of 10×10 cm 2 tripleGEM detectors operated with several gas mixtures. In a previous paper we pointed out that adding CF4 to the standard Ar/CO2 gas mixture allows to improve the time resolution of the detector from ∼ 10 ns down to ∼ 6 ns (r.m.s.). In this paper we discuss the results obtained with CF4 and iso-C4H10 based gas mixtures, during a beam test at the πM1 beam facility of the Paul Scherrer Institute (PSI). Preliminary results concerning the discharge probability of triple-GEM detector, when exposed to both high intensity pion/proton beam and α-particles from a radioactive source are presented. Gain measurements and aging tests, using a high intensity 5.9 keV X-ray tube, are eventually discussed.

The triple-GEM detector for the M1R1 muon station at LHCb

Twenty-four triple-GEM detectors with 20times24 cm2 active area will equip the inner region of the first station of the muon detector at the LHCb experiment. After three years of R&D to prove that this detector, operated with a CF4 based gas mixture, satisfies the stringent requirements in terms of time performance and radiation hardness, the project is entering in the construction phase. The final design of the detector, the selected materials and the construction procedure and tools will be described in details. The quality control of components, such as planarity measurements on the PCB-panels and the HV test of the GEM foil, as well as the leak test and the X-ray tomography of constructed chambers will be discussed. The chamber equipped with front end electronics, Faraday cage and HV divider is finally tested with cosmics. The construction of the detector, shared between the two production sites of Cagliari-INFN and Laboratori Nazionali di Frascati-INFN, should be completed in spring 2006. The installation is foreseen by the end of the 2006

Applications of triple GEM detectors beyond particle and nuclear physics

Micro-Pattern Gaseous Detectors (MPGD) have opened the way for the construction of detectors whose performance surpasses that of the previous generations in terms of spatial resolution, high-rate capability and increased radiation hardness. Led by the Micro-Mesh Gaseous Structure (Micromegas) and the Gas Electron Multiplier (GEM), some MPGDs are mature technologies used in a variety of experiments at high energy physics. What we report in this article is the experience explored in the last years with a compact GEM detector system in several applications as medical imaging, dosimetry and beam diagnostics for high energy beams and for nuclear reactors. For sake of shortness, only performance on soft X-ray and neutron detection will be described in detail. Also a description of the new promising highly pixelated GEM detector will be presented.

Diffraction measurements with a boron-based GEM neutron detector

The research of reliable substitutes of 3He detectors is an important task for the affordability of new neutron scattering instrumentation for future spallation sources like the European Spallation Source. GEM (Gas Electron Multiplier)-based detectors represent a valid alternative since they can combine high-rate capability, coverage of up to area and good intrinsic spatial resolution (for this detector class it can be better than 0.5 mm). The first neutron diffraction measurements performed using a borated GEM detector are reported. The detector has an active area of and is equipped with a borated cathode. The GEM detector was read out using the standard ISIS Data Acquisition System. The comparison with measurements performed with standard 3He detectors shows that the broadening of the peaks measured on the diffractogram obtained with the GEM is 20–30% wider than the one obtained by 3He tubes but the active area of the GEM is twice that of 3He tubes. The GEM resolution is improved if half of its active area is considered. The signal-to-background ratio of the GEM is about 1.5 to 2 times lower than that of 3He. This measurement proves that GEM detectors can be used for neutron diffraction measurements and paves the way for their use at future neutron spallation sources.

3He-free triple GEM thermal neutron detector

A novel type of thermal neutron detector based on the gas electron multiplier (GEM) technology is presented in the framework of the research and development activity on the 3He replacement for neutron detection. The device relies on a series of boron-coated alumina sheets placed perpendicularly to the incident neutron beam direction. The detector, named side-on GEM (S-GEM), was tested on beam at the High Flux Isotope Reactor at the Oak Ridge National Laboratory (US) to assess its performance in terms of beam position resolution, efficiency and signal-to-background (S/B) ratio as compared to a 10 bar 3He tube for sub-thermal neutrons. Using 3 mm wide PADs, a sub-millimeter position resolution was obtained. The achieved efficiency is about 30% with a quite good S/B ratio. The obtained results demonstrate the effectiveness of the proposed detector configuration to achieve a good spatial resolution and, in the perspective, a higher thermal neutron efficiency, comparable to 3He tubes typically used for diagnostic in nuclear reactors. The main issues to be addressed to reach the goal, mostly related to boron coating procedures and characterization, are also pointed out.

The LHCb triple-GEM detector for the inner region of the first station of the muon system: construction and module-0 performance

A triple-gas electron multiplier (GEM) detector, operated with the gas mixture Ar/CO2/CF4 (45/15/40), is going to equip station M1, region R1 of the LHCb muon system. A Module-0 of this detector, with full area (20 cmtimes24 cm) GEM foils, was recently built and tested. In this paper, new measurements of efficiency and pad multiplicity are presented. These new measurements were very important to select of the final pad board configuration. The sensitivity to discharges is a very important issue in this type of detector; we discuss here new measurements of the maximum number of discharges that a triple-GEM detector can stand before breakdown, and we show that detector operation in LHCb is safe from this point of view. We also discuss new measurements of the time performance of the detector in the presence of background radiation, indicating that no significant deterioration of the performances is expected in the LHCb environment

Measurement of an accelerator based mixed field with a Timepix detector

We present an analysis of a high energy mixed field taken with a Timepix chip at the CERF facility at CERN. The Timepix is an active array of 65K energy measuring pixels which allows visualization and energy measurement of the tracks created by individual particles. This allows characteristics of interest such as the LET and angular distributions of the incoming tracks to be calculated, as well as broad morphological track categories based on pattern recognition techniques. We compute and compare LET-like and angular information for different morphological track categories. Morphological track categories are found to possess overlapping LET and energy spectra, however the approaches are found to be complementary with morphological clustering yielding information which is indistinguishable on the basis of LET alone. The use of the Timepix as an indirect monitoring device outside of the primary beam at CERF is briefly discussed.

Particle tracking with a Timepix based triple GEM detector

This paper details the response of a triple GEM detector with a 55 μmetre pitch pixelated ASIC for readout. The detector is operated as a micro TPC with 9.5 cm3 sensitive volume and characterized with a mixed beam of 120 GeV protons and positive pions. A process for reconstruction of incident particle tracks from individual ionization clusters is described and scans of the gain and drift fields are performed. The angular resolution of the measured tracks is characterized. Also, the readout was operated in a mixed mode where some pixels measure drift time and others charge. This was used to measure the energy deposition in the detector and the charge cloud size as a function of interaction depth. The future uses of the device, including in microdosimetry are discussed.

Real-time measurements of radon activity with the Timepix-based RADONLITE and RADONPIX detectors

Radon gas is the most important source of ionizing radiation among those of natural origin. Two new systems for radon measurement based on the Timepix silicon detector were developed. The positively charged radon daughters are electrostatically collected on the surface of the Si detector and their energy spectrum measured. Pattern recognition of the tracks on the sensor and particle identification are used to determine number and energy of the alpha particles and to subtract the background, allowing for efficient radon detection. The systems include an algorithm for real-time measurement of the radon concentration and the calculation of the effective dose to the lungs.

Aging measurements on triple-GEM detectors operated with CF/sub 4/-based gas mixtures

We present the results of a global irradiation test of full size triple-GEM detectors operated with CF/sub 4/-based gas mixtures. This study has been performed in the framework of an R&D activity on detectors for the innermost region of the first muon station of the LHCb experiment. The prototypes have been irradiated at the Calliope facility of the ENEA-Casaccia with a high intensity 1.25 MeV /spl gamma/ from a /sup 60/Co source. After the irradiation test the detectors performances have been measured with X-rays and with a 3 GeV pion beam at CERN. A SEM analysis on several samples of the detectors has been performed to complete the understanding of the physical processes occurring in the GEM detector during the strong irradiation.