Saturated fluorocarbons (SFCs) of the form CnF(2n+2) are chosen for their optical properties (high transparency in the near UV, adapted refractive index and low chromatic dispersion over wavelength ...ranges of interest) for use as Cherenkov radiators. The COMPASS and LHCb experiments currently use C4F10 and CF4 gas radiators. SFCs have high Global Warming Potentials (GWPs), however (in the range 5000–9000). There is thus an impetus to reduce their use and wastage through leaks in existing installations.
Newer fluids of the form CnF2nO, including the 3M NOVEC® range, can offer similar optical performance to SFCs of the same order, n, but with GWPs equivalent to CO2. These GWPs are, however, geometry-specific: closed molecular rings having an oxygen atom as a link can have GWPs as high as those of SFCs, and should be avoided.
While the optical constraints of RICH detectors can motivate a “special case” argument to retain the use of preferred SFCs, legislation and external market forces will limit their future availability, leaving “holes” in the CnFx spectrum that might not be filled by NOVEC equivalents. This situation might require the blending of low molar concentrations of heritage-stock higher-order SFCs and NOVEC vapours with transparent light gases such as nitrogen, and is the subject of this paper.
While continuous optical measurement of refractive index in dynamically changing gas mixtures is very demanding, the monitoring of sound velocity has been historically shown to provide simple, reliable and continuous real time mixture information. Indeed the speed of sound is, in itself, a monitor of the speed of light and the Cherenkov threshold in a gas radiator.
This ultrasonic (“sonar”) technique was first used for controlling the real-time blending C5F12 with N2 in the SLD CRID at the SLAC linear collider. The technique could become important again in future operation to meet the optical and low GWP constraints of future Cherenkov gas radiators. Some examples are explored in this paper.
Radiation detectors dedicated to time-of-flight positron emission tomography (PET) have been developed, and coincidence time resolution (CTR) of sub-100 ps full width at half maximum (FWHM) has been ...achieved by carefully optimizing scintillators and photodetectors. Achieving a CTR of 30 ps FWHM by using a pair of annihilation γ-rays would allow us to directly localize the annihilation point within an accuracy of 4.5 mm. Such direct localization can potentially eliminate the requirement of image reconstruction processes in clinical PET systems, which would have a huge impact on clinical protocols and molecular imaging. To obtain such a high CTR, researchers have investigated the use of prompt emissions such as Cherenkov radiation and hot-intra band luminescence. Although it is still challenging to achieve a CTR of 30 ps FWHM even with a Cherenkov-based detector, the experimentally measured CTR is approaching the goal. In this work, we developed a Cherenkov-radiator-integrated micro-channel plate photomultiplier tube (CRI-MCP-PMT), where there are no optical boundaries between the radiator and photocathode, and its timing performance was investigated. By removing the optical boundaries, reflections are eliminated and transmission to the photocathode is improved, resulting in high timing capability. As a result, a CTR of 30.1 ± 2.4 ps FWHM, which is equivalent to a position resolution of 4.5 ± 0.3 mm along a line of response (LOR), was obtained by using a pair of CRI-MCP-PMTs.
Study of new aerogel radiators for the LHCb RICH upgrade Lozar, Andrej; Keizer, Floris; D’Ambrosio, Carmelo ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2023, Letnik:
1056
Journal Article
Recenzirano
Odprti dostop
As a part of the LHCb RICH Future upgrades experimental program, we studied hydrophobic aerogel tiles from Chiba University during the 2021 CERN SPS testbeam. In a 180 GeV/c proton beam, we tested ...aerogels with different refractive indices and different thicknesses. The Cherenkov light radiated from aerogel tiles was focused by a lens and registered by an array of MAPMTs. The number of detected photons per Cherenkov ring for a 2 cm thick aerogel tile with refractive index of 1.03 was around eight and in good agreement with the Monte Carlo simulation. We estimate the photon production yield to be about 50 photons/cm.
At the Institute for Nuclear Physics in Mainz the new electron accelerator MESA will go into operation within the next years. The high-power beam dump of the P2 experiment is ideally suited for a ...parasitic dark sector experiment — DarkMESA. In the first stage 1,000 high density Cherenkov radiators from a previous experiment will be used. The experiment is studied with a simulation based on MadGraph and Geant4. The simulation includes an optical photon study, where the response of possible calorimeter materials – PbF2, BGO, the Pb glasses SF5, SF6 and SF57HTultra from Schott – was investigated. The simulation outcomes are compared with the results of prototypes tested at the Mainz Microtron (MAMI) with 6 to 14 MeV electrons. The exclusion limits for PbF2 are shown, together with the limits obtained incrementally adding Pb glass blocks in two successive phases. The current development status of a prototype detector will be described, including a concept for a cosmics veto system.
Status of high-quality silica aerogel radiators Adachi, Ichiro
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Letnik:
952
Journal Article
Recenzirano
Silica aerogels have been used widely in high-energy and nuclear physics experiments. Recent developments of highly transparent aerogels have further enabled the utilization of Cherenkov radiators in ...RICH counters for many experiments. This paper reviews the progress of high-quality aerogels by describing the two optical parameters of transmittance and refractive index, and some issues in its application will be presented.
Development of transparent silica aerogel over a wide range of densities Tabata, Makoto; Adachi, Ichiro; Ishii, Yoshikazu ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2010, Letnik:
623, Številka:
1
Journal Article
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We have succeeded in developing hydrophobic silica aerogels over a wide range of densities (i.e. refractive indices). A pinhole drying method was invented to make possible producing highly ...transparent aerogels with entirely new region of refractive indices of 1.06–1.26. Obtained aerogels are more transparent than conventional ones, and the refractive index is well controlled in the pinhole drying process. A test beam experiment was carried out in order to evaluate the performance of the pinhole-dried aerogels as a Cherenkov radiator. A clear Cherenkov ring was successfully observed by a ring imaging Cherenkov counter. We also developed monolithic and hydrophobic aerogels with a density of 0.01g/cm3 (a low refractive index of 1.0026) as a space dust capturer for the first time. Consequently, aerogels with any refractive indices between 1.0026 and 1.26 can be produced freely.
•The Belle II A-RICH counter requires transparent silica aerogel Cherenkov radiators.•Required refractive index of hydrophobic aerogel tiles is approximately 1.05.•Mass production of large-area ...(18cm×18cm×2cm), crack-free aerogel tiles is vital.•A method for producing aerogel tiles satisfying all requirements is established.•Crack-free aerogel tiles are ensured by pressure control in the supercritical drying.
This study presents the development of large-area (18cm×18cm×2cm), high refractive index (n∼1.05) hydrophobic silica aerogel tiles for use as Cherenkov radiators. These transparent aerogel tiles will be installed in a Cherenkov detector for the next-generation accelerator-based particle physics experiment Belle II, to be performed at the High Energy Accelerator Research Organization (KEK) in Japan. Cracking has been eliminated from the prototype aerogel tiles by improving the supercritical carbon dioxide (scCO2) extraction procedure when drying the wet gel tiles. Finally, a method of mass-producing aerogel tiles for the actual detector was established. It was confirmed that the experimentally manufactured aerogel tiles meet the required optical and hydrophobic characteristics and have a uniform tile density.
We have developed a RICH counter as a new forward particle identification device for the Belle II experiment. As a Cherenkov radiator in this counter, a dual aerogel layer combination consisting of ...two refractive indicies, n=1.045 and 1.055, is employed. Mass production of these aerogel tiles has been done during 2013–2014 with new method improved by Chiba group. Optical qualities for them have been examined. The refractive indices of the obtained tiles were found to be in good agreement with our expectations, and the transparencies were high enough to be used for the RICH radiator.
Hydrophobic silica aerogel production at KEK Tabata, Makoto; Adachi, Ichiro; Kawai, Hideyuki ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2012, Letnik:
668
Journal Article
Recenzirano
We present herein a characterization of a standard method used at the High Energy Accelerator Research Organization (KEK) to produce hydrophobic silica aerogels and expand this method to obtain a ...wide range of refractive index (n=1.006–1.14). We describe in detail the entire production process and explain the methods used to measure the characteristic parameters of aerogels, namely the refractive index, transmittance, and density. We use a small-angle X-ray scattering (SAXS) technique to relate the transparency to the fine structure of aerogels.
Despite its success in the SLD CRID at the SLAC Linear Collider, ultrasonic measurement of Cherenkov radiator refractive index has been less fully exploited in more recent Cherenkov detectors ...employing gaseous radiators. This is surprising, since it is ideally suited to monitoring hydrostatic variations in refractive index as well as its evolution during the replacement of a light radiator passivation gas (e.g. N2, CO2) with a heavier fluorocarbon (e.g. C4F10CF4; mol. wt. 18888). The technique exploits the dependence of sound velocity on the molar concentrations of the two components at known temperature and pressure. The SLD barrel CRID used an 87%C5F12/13%N2 blend, mixed before injection into the radiator vessel: blend control based on ultrasonic mixture analysis maintained the β=1 Cherenkov ring angle to a long term variation better than ±0.3%, with refractivity monitored ultrasonically at multiple points within the radiator vessel.
Recent advances using microcontroller-based electronics have led to ultrasonic instruments capable of simultaneously measuring gas flow and binary mixture composition in the fluorocarbon evaporative cooling systems of the ATLAS Inner Detector. Sound transit times are measured with multi-MHz transit time clocks in opposite directions in flowing gas for simultaneous measurement of flow rate and sound velocity. Gas composition is evaluated in real-time by comparison with a sound velocity/composition database.
Such instruments could be incorporated into new and upgraded gas Cherenkov detectors for radiator gas mixture (and corresponding refractive index) measurement to a precision better than 10−3. They have other applications in binary gas analysis - including in Xenon-based anaesthesia. These possibilities are discussed.
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