High Counting Research Articles

A New Anti-Interfering Platelet Counting Technology Utilizing Conventional Impedance and White Blood Cell Differential Channel.

Accurate platelet (PLT) counting is crucial for disease diagnosis and treatment, especially under the condition of thrombocytopenia and platelet transfusion. A few PLT counting approaches have been established including impedance and fluorescent methods. The impedance PLT counting (PLT-I) approach could be interfered by small non-PLT particles in the blood, such as RBC/WBC fragments, microcytes, bacteria, and cryoglobulins. The fluorescent PLT counting methods provide a more accurate but rather costly option. Thus, it is highly desirable to develop a new economic-friendly approach with accurate platelet count. In this study, we introduced a novel hybrid PLT counting (PLT-H) strategy to combine the count of smaller-sized PLTs from impedance channel and larger-sized PLTs from conventional white blood cell (WBC) channel to realize a low-cost PLT count with high accuracy. Blood samples with different PLT levels and no significant interfering factors (confirmed by blood smear) were collected. The PLTs were counted with BC-6800Plus (PLT-I) and compared with the PLT counts from the CD41/CD61 immunoplatelet (immunoPLT) reference method using Beckman Coulter FC-500 flow cytometer. In addition, the morphology and internal structure of PLT treated with hemolytic agents of conventional WBC channel was observed with phase contrast microscopy and electron microscopy. Then the counting accuracy of PLT-H was assessed by comparing PLT count results between BC-720 (PLT-H) and the CD41/CD61 immunoPLT reference method. By comparing PLT-I with immunoPLT, it was found that the impedance PLT counting result will not be interfered by small non-PLT particles when the size of PLT smaller than 10 fL. For large PLT (> 10 fL), PLT count in conventional WBC channel shows good correlations with immunoPLT. Furthermore, after treated with hemolytic agents the PLT still preserves an intact cellular structure and swells slightly, while RBCs are lysis and disappeared upon hemolytic treatment. Lastly, the novel PLT-H result exhibits a good correlation with immunoPLT with a high correlation factor (r = 0.9911). The new PLT counting method PLT-H achieves high accuracy in blood samples with low-cost, and it provide a novel strategy of combining traditional methods for high accurate counting in hematology laboratories.

Performance Characteristics of a New Generation 148-cm Axial Field-of-View uMI Panorama GS PET/CT System with Extended NEMA NU 2-2018 and EARL Standards.

The uMI Panorama GS PET/CT system is a new long-axial-field-of-view scanner featuring high sensitivity, time-of-flight (TOF) resolution, spatial resolution, and count rate performance. The aim of this study is to assess the PET system on the basis of the National Electrical Manufacturers Association (NEMA) NU 2-2018 and European Association of Nuclear Medicine Research Limited (EARL) standards. Methods: Spatial resolution, count rate performance, sensitivity, accuracy, image quality, TOF resolution, and coregistration accuracy were evaluated following the NEMA NU 2-2018 standard. Additional experiments included energy resolution, 200-cm-long line sources for sensitivity, a 175-cm-long scatter phantom for count rate and TOF resolution, as well as the compliance with the EARL guideline. Moreover, an 18F-FDG PET patient study was reconstructed with various frame durations. Results: The PET system achieved sub-3-mm transaxial and axial spatial resolutions at a 1-cm radial offset. The sensitivities with the 70-cm-long and 200-cm-long line sources were observed to be 176.3 and 90.8 kcps/MBq, respectively, at the center of the field of view. The noise-equivalent count rates (NECRs) of the 70-cm-long and 175-cm-long scatter phantoms were measured to be 3.35 Mcps at 57.57 kBq/mL and 2.24 Mcps at 33.27 kBq/mL, respectively. The TOF resolutions for both phantoms were approximately 189 ps at 5.3 kBq/mL and lower than 200 ps below the NECR peaks. The absolute count rate errors of all 34 acquisitions were less than 3% below the NECR peak for the 70-cm-long scatter phantom. With the standard NEMA image quality phantom experiment, the contrast recovery coefficient varied from 68.17% to 94.20% and the background variabilities were all below 2%. The maximum PET/CT coregistration error was 1.33 mm. Regarding EARL compliance, the gaussian filter of 5-mm full width at half maximum could produce acceptable images. The patient data demonstrate visually satisfactory image quality with short frames (less than 1 min). Conclusion: The uMI Panorama GS exhibits spatial resolution and TOF resolution similar to those of the uMI Panorama system (35-cm axial field of view), despite the extended axial field of view. The 148-cm axial coverage, sub-200-ps TOF resolution, high sensitivity, and count rate performances are expected to yield superior image quality and offer new opportunities for various clinical applications.

Review of thermal neutron scintillators: Evaluation metrics and future prospects for demanding applications

Neutron applications are progressing rapidly, requiring detectors to meet increasingly rigorous criteria. Specifications such as high neutron counting rates, fast timing resolution and low background have a significant impact on choice of scintillator and how scintillators are evaluated. This work considers detector requirements for neutron scattering instruments that are becoming more stringent as the sources and scattering technologies continue to improve. Meanwhile, both prominent scintillators used for neutron scattering detectors, ZnS:Ag/6LiF and GS-glass, remain stagnant. While these scintillators have been suitable for many years, they are becoming a limiting factor for neutron scattering instruments. ZnS:Ag is inhibiting count rate capability and GS-glass is too gamma sensitive so alternatives need to be found. A brief explanation of neutron scattering, its detector requirements and how those relate to scintillator properties will be discussed. Furthermore, this work explains how standard characterization methods and reporting of scintillation properties are not entirely suitable for high count rate, low background applications like neutron scattering. As a result, modifications to characterization of gamma discrimination, light output, and decay kinetics are suggested. Additional steps are suggested including neutron activation and a more appropriate assessment of count rate capability. A non-exhaustive set of 6Li containing neutron sensitive scintillators including ZnS:Ag/6LiF, GS20 glass, ZnO:Zn/6LiF, Cs6LiYCl:Ce, 6LiI:Eu, 6LiI:Ce, 6LiCaAlF:Eu, LiCaAlF:Ce, transparent rubber sheet (TRUST) 6LiCaAlF:Eu, TRUST 6LiCaAlF:Eu with added fluorophore and EJ-270 (6Li containing plastic) are reviewed and studied from this different perspective. Finally, new scintillator developments relevant to high count rate, low background applications are discussed.

Effects of the passive voltage divider in a photomultiplier tube: Analytical model, simulations and experimental validation

The effects of the passive resistive voltage divider network in a photomultiplier tube (PMT) have been investigated by developing an in-house Monte Carlo simulation code and compared with experimental measurements and an analytical model. The simulation code follows an iterative procedure that takes into account the transport and amplification of the electrons within the device depending on the electrostatic fields produced by the electrode voltages. The PMT gain, dynode voltages, rise time and transit time have been studied as a function of the photocathode current and supply voltage. A good agreement between the analytical model, the simulations and numerous experimental measurements using a Hamamatsu R13408-100 PMT has been obtained. The simulation results endorse the use of logistic functions within the analytical model to account for the collection efficiency in the last dynode stages. This works deepens the understanding of passive voltage dividers and develops an advanced behavioral circuit model of photomultiplier tubes. Although validated for a single PMT, the proposed methodology is applicable to any PMT model. This aids in optimizing the design of fully active voltage dividers, to be applied in extremely pulsed applications with high count rates such as prompt gamma-ray imaging during proton therapy.

Study on background full simulation and implementation for Super Tau-Charm Facility

The Super Tau-Charm Facility is a new generation high luminosity electron-positron collider designed to operate in the tau-charm energy region. With the designed peak luminosity of at least 0.5 × 1035 cm-2s-1, the background full simulation and implementation would be an important part in the detector study. Based on Offline Software of Super Tau-Charm Facility, the software platform for STCF, the spectrometer structure modeling, simulation for both luminosity-related and beam-related background sources, the random mixing algorithm of signal and background are carried out. The simulation result indicates that the highest TID in STCF detector is 4700 Gy/y, the highest NIEL damage is below 1011 1 MeV neutron·cm-2y-1 except MDC, and the highest SEEs is below 2 kHz/cm2. The cross check with FLUKA also indicates a similar magnitude for both the TID and NIEL damage simulation result, except MDC NIEL damage due to the (n, p) reaction was not considered in FLUKA. The highest background total count rate is hundreds of MHz for most of detectors, the highest count rate per channel is approximately 720 kHz/channel in ITKW and 580 kHz/channel in ECAL. This work presents a systematic background evaluation route based on GEANT4, which is easy to combine with the further detector performance study. These simulation results indicate that all the systems can tolerate the background with the newly developed detector and electronics technologies. Moreover, the further optimization of STCF lattice design, the shield in MDI and detector systems are still required to suppress the background to an even lower level for a better detector performance. Meanwhile, the physics signal can be well mixed with the randomly sampled background data at the level of GEANT4 steps, aiming to simulate the realistic situation of the detector and providing necessary database for detector performance optimization and physics study.

Performance Investigations of Two Channel Readout Configurations on the Cross-Strip Cadmium Zinc Telluride Detector.

In a detector system where the number of channels exceeds the number of channels available on an application-specific integrated circuit (ASIC), there is a need to configure channels among multiple ASICs to achieve the lowest electronic noise and highest count rate. In this work, two board configurations were designed to experimentally assess which one provides the more favorable performance. In the half-half configuration, contiguous channels from one edge to the center of CZT detector are read by one ASIC, and the other half are read by the other ASIC. In the alternate configuration, the CZT channels are read by alternating ASICs. A lower electronic noise level, better FWHM energy resolution performance (5.35% ± 1.08% compared to 7.84% ± 0.98%), and higher count rate was found for the anode electrode strips with half-half configuration. Cross-talk between ASICs and deadtime play a role in the different performances, and the total count rate of the half-half configuration has a count rate 18.1% higher than that of the alternate configuration.

High-count-rate particle tracking in proton and carbon radiotherapy with Timepix2 operated in ultra-short acquisition time

This work investigates the operational acquisition time limits of Timepix3 and Timepix2 detectors operated in frame mode for high-count rate of high deposited energy transfer particles. Measurements were performed using alpha particles from a 241Am laboratory source and proton and carbon ion beams from a synchrotron accelerator. The particle count rate upper limit is determined by overlapping per-pixel particle signals, identifiable by the hits per pixel counter > 2, indicating the need to decrease acquisition time. On the other hand, the lower limit is the time required to collect the particle deposited charge while maintaining spectral properties. Different acquisition times were evaluated for an AdvaPIX Timepix3 detector (500 μm Silicon sensor) with standard per-pixelDigital to Analog Converter (DAC)settings and a Minipix Timepix2 detector (300 μm Silicon sensor) with standard and customized settings the pulse shaping parameter and threshold. For AdvaPIX Timepix3, spectra remained accurate down to 100 μs frame acquisition time; at 10 μs, loss of collected charge occurred, suggesting either avoiding this acquisition time or applying a correction. Timepix2 allowed acquisition times down to 100 ns for single particle track measurements even for high energy loss, enabled by a new Timepix2 feature delaying shutter closure until full particle charge collection. This work represents the first measurement utilizing Timepix-chips pixel detectors in an accelerator beam of clinical energy and intensity without the need to decrease the beam current. This is made possible by exploiting the short shutter feature in Timepix2 and a customized per-pixel energy calibration of the Timepix2 detector with a larger discharging signal value which allowed for shorterTime-over-Threshold (ToT)signal. These customized settings extend the operation of the pixel detectors to higher event rates up to 109 particles/cm2/s.

Initial results of the Hyperion IIDPET insert for simultaneous PET-MRI applied to atherosclerotic plaque imaging in New-Zealand white rabbits.

In preclinical research, in vivo imaging of mice and rats is more
common than any other animal species, since their physiopathology is very well-
known and many genetically altered disease models exist. Animal studies based on
small rodents are usually performed using dedicated preclinical imaging systems
with high spatial resolution. For studies that require animal models such as mini-
pigs or New-Zealand White (NZW) rabbits, imaging systems with larger bore
sizes are required. In case of hybrid imaging using Positron Emission Tomography
(PET) and Magnetic Resonance Imaging (MRI), clinical systems have to be used,
as these animal models do not typically fi t in preclinical simultaneous PET-MRI
scanners.
Approach. In this paper, we present initial imaging results obtained with the
Hyperion IID PET insert which can accommodate NZW rabbits when combined
with a large volume MRI RF coil. First, we developed a rabbit-sized image
quality phantom of comparable size to a NZW rabbit in order to evaluate the
PET imaging performance of the insert under high count rates. For this phantom,
radioactive spheres with inner diameters between 3.95 and 7.86 mm were visible
in a warm background with a tracer activity ratio of 4.1 to 1 and with a total
18-F activity in the phantom of 58MBq at measurement start. Second, we performed
simultaneous PET-MR imaging of atherosclerotic plaques in a rabbit in vivo using
a single injection containing 18-F-FDG for detection of infl ammatory activity,
and Gd-ESMA for visualization of the aortic vessel wall and plaques with MRI.
Main results. The fused PET-MR images reveal 18-F-FDG uptake within an
active plaques with plaque thicknesses in the sub-millimeter range. Histology
showed colocalization of 18-F-FDG uptake with macrophages in the aortic vessel wall lesions. 
Significance. Our initial results demonstrate that this PET insert
is a promising system for simultaneous high-resolution PET-MR atherosclerotic
plaque imaging studies in NZW rabbits.

Record high counting rate of positron annihilation lifetime spectrometer achieved by [formula omitted] coincidence

Conventional positron annihilation lifetime (PAL) spectrometers, which employ the γ-γ coincidence with two perpendicularly-positioned detectors, have a typical counting rate of 100–300 counts per second (cps). To increase the counting rate, according to the optimized structural parameters using Geant4 simulation, a 22Na positron source (∼ 1.665 MBq), a silicon photomultiplier (SiPM), and digital waveform technology are utilized for the first time to a β+-γ coincidence PAL spectrometer. After the optimization and verification of accuracy and stability, this spectrometer can achieve a time resolution of about 206 ps, and a record high effective counting rate of approximately 19000 cps (∼ 11000 cps/MBq), which is two orders of magnitude greater than those of conventional PAL spectrometers. The significant shortening of measurement time for a single PAL spectrum enables us to observe sub-minute-scale evolution of microstructure during rapid physical and chemical processes in the future.

Performance evaluation of a small-animal PET scanner with 213 mm axis using NEMA NU 4-2008.

Long-axis positron emission tomography (PET) has emerged as one of the recent research directions in PET due to its ability to significantly enhance sensitivity and counting performance for low-dose imaging, rapid imaging, and whole-body dynamicimaging. The PET system presented in this study is a long-axis animal PET based on lutetium-yttrium orthosilicate and silicon photomultiplier, designed for whole-body imaging in rats. It features a diameter of 143 mm and an axial length of 213.3 mm. This study evaluated the performance of this PET system in accordance with the National Electrical Manufacturers Association (NEMA) NU 4-2008standards. The performance evaluation was conducted according to the NEMA NU 4-2008 standards in terms of spatial resolution, sensitivity, counting rate performance, scatter fraction (SF) and image quality. In addition, a rat imaging study was conducted to assess the imaging capability of this PETsystem. The average energy resolution of the PET system was 12.87%, the average coincidence timing resolution was 751 ps. The FWHM of spatial resolution reconstructed by filtered back projection and 3D-OSEM-PSF algorithm at 5 mm radial offset from the axial center were 1.65 and 0.88 mm. The peak absolute sensitivity measured by a point source at the center of the field of view was evaluated as 6.71% (361-661keV) and 10.31% (250-750 keV). For the mouse-like phantom, the SF was 11.0% and the peak noise equivalent counting rate (NECR) was 1193 kcps at 94.2 MBq (2.54 mCi). For the rat-like phantom, the SF was 26.8% and the NECR was 682.5 kcps at 78.6 MBq (2.12 mCi). The performance measurement results demonstrate that this PET system exhibits high sensitivity and count rate performance, making it potential for high-quality whole-body dynamic imaging ofrats.

Cerium doped yttrium aluminum perovskite scintillator as an absolute ultracold neutron detector.

The upcoming UCNProBe experiment at Los Alamos National Laboratory will measure the beta decay rate of free neutrons with different systematic uncertainties than previous beam-based neutron lifetime experiments. We have tested a new 10B-coated Yttrium Aluminum Perovskite (YAP:Ce) scintillator and present its properties. The advantages of the YAP:Ce scintillator include its high Fermi potential, which reduces the probability for upscattering of ultracold neutrons (UCN), and its short decay time, which increases sensitivity at high counting rates. Birks' coefficient of YAP:Ce was measured to be (5.56-0.30+0.05)×10-4 cm/MeV. The loss of light due to the 120nm 10B-coating was measured to be about 60%, and the loss of light from YAP:Ce due to transmission through a deuterated polystyrene scintillator was about 50%. The efficiency for neutron capture on the 10B coating was (86.8 ± 2.6)%, and a measurement using UCN showed that the YAP:Ce crystal counted 8%-28% more UCN compared to a ZnS:Ag screen. The difference may be due to the uneven coating of 10B on the rough surface of ZnS:Ag.

A single photon resolution integrating chip for silicon microstrip sensors (SSDROC) in High Energy Photon Source

Single-photon counting silicon microstrip detectors play a crucial role in X-ray powder diffraction experiments due to their high sensitivity and low dead-time. The High Energy Photon Source (HEPS) is poised to become a world-leading facility for high-energy synchrotron radiation. The storage ring, being constructed in China, will operate at an electron energy of 6 GeV and an emittance of less than 0.06 nm rad, thereby providing an exceptionally bright synchrotron light beam.Consequently, there is a requirement for detectors at HEPS to possess enhanced photon counting capabilities. Our team developed a dedicated Application-Specific Integrated Circuit (SSDROC) and a readout electronics system for one-dimensional X-ray detection. To resolve the issue of inconsistent photon response across different channels, a novel secondary calibration method has been applied. The detector has undergone various performance tests, and the results show that the entire system has good linearity, high energy resolution, and a high count rate.

A novel detector for 4D tracking in particle therapy

An innovative beam monitor for particle therapy applications was developed to count protons and carbon ions in clinical beams and was integrated with a Time-to-Digital Converter (TDC) to add the measurement of particles’ crossing time. The detector exploits strip-segmented planar silicon sensors with an active thickness of a few tens of μm and the front-end electronics is based on a 24-channel ASIC (named ABACUS) for the discrimination of the particles’ signals. The proton counting efficiency shows a dependence on the beam energy because of transversal dimension and pile-up effects, whereas an efficiency between 94 and 98 % with lower energy dependence is found for carbon ions. The time measurements with the TDC allow for the study of the time interval between consecutive particles in one strip, which appears to be compatible with the radio-frequency period of the synchrotron. These results indicate that thin silicon sensors and custom front-end readout with high counting rate capability allow for a full 4D tracking of clinical ion beams, opening the way to future technologies for online monitoring systems.

Study of readout system for 3He linear position sensitive detectors

This study introduces a readout system for 3He linear position-sensitive detectors (LPSDs), tailored for the Small Angle Neutron Scattering (SANS) spectrometer of the Compact Pulsed Hadron Source (CPHS) at Tsinghua University. Central to this system is the employment of a trapezoidal filter as the primary signal shaper, selected for its enhanced noise filtering capabilities and efficacy in mitigating ballistic deficit. Additionally, the integration of a digital CR filter aims to counteract baseline drift within trigger signals. This innovative architecture underwent validation via computer programs using experimental data, demonstrating superior performance in spatial resolution compared to conventional Gaussian filter-based approaches. Meanwhile, the improvement in spatial resolution comes with a narrower pulse width, promising a higher throughput at high count rates. When applied to a 16-tube detector module, the system achieved an average position resolution of 3.63 mm (FWHM) at the central region and 4.03 mm at the end regions. Furthermore, with a pusle width of 0.6 μs, the 96-tube detector array is promised to sustain a count rate over 1 Mcps.

Study of the effect of detector to front-end electronics distance on the spectrometric performances of solid-state detectors

Solid-state detectors are used for charge particles detection and spectrometry with front-end electronics located, usually, next to the detectors. Therefore, in some applications, due to high-level radiation, high temperature and/or electro-magnetic noises (e.g. in nuclear fusion energy experiments, high energy accelerators, etc.) there could be the need to locate the front-end electronics far away from the detector. To solve the problem a matching sensitive charge amplifier (MSCA) with AC coupled input was designed by Roberto Cardarelli (former INFN scientist) for measurements at the fusion JET tokamak (U.K.). The prototype, composed of two amplification stages, was “ad hoc” designed for use with Diamond detectors and resulted very reliable. A commercial version of the MSCA was then developed and is now available on the market. Its novelty and main advantage, with respect to the former version, is to be used also with other fast detectors e.g. Resistive Plate Chamber (RPC) with high counting speed and Silicon detectors. The commercial MSCA features input impedance very close to 50 Ohm, which can be matched to a 50-Ohm transmission line. This allows locating the amplifier at variable distances from the detector and up to 100 m. These claimed performances result very interesting for solid state detectors, therefore, up to now a few applications of MSCA are reported in the literature and a systematic study of its performances is missing. In this work, an analysis of the spectrometric performances of Diamond and Silicon detectors coupled to MSCA located at various distances (up to 48 m) from the detectors is reported. Pulse height spectra of a multi-peaks alpha source were measured using MSCA amplifier and compared with those obtained using a standard charge sensitive preamplifier (CA). Then, the effect of the distance between detectors and amplifiers was investigated using standard RG58 and double shielded RG214 coaxial cables. The results are presented and discussed.

Quantitative Analysis with EDS and WDS at High Count Rates

Quantitative Analysis with EDS and WDS at High Count Rates

Efficient, nonparametric removal of noise and recovery of probability distributions from time series using nonlinear-correlation functions: Photon and photon-counting noise.

A preceding paper [M. Dhar, J. A. Dickinson, and M. A. Berg, J. Chem. Phys. 159, 054110 (2023)] shows how to remove additive noise from an experimental time series, allowing both the equilibrium distribution of the system and its Green's function to be recovered. The approach is based on nonlinear-correlation functions and is fully nonparametric: no initial model of the system or of the noise is needed. However, single-molecule spectroscopy often produces time series with either photon or photon-counting noise. Unlike additive noise, photon noise is signal-size correlated and quantized. Photon counting adds the potential for bias. This paper extends noise-corrected-correlation methods to these cases and tests them on synthetic datasets. Neither signal-size correlation nor quantization is a significant complication. Analysis of the sampling error yields guidelines for the data quality needed to recover the properties of a system with a given complexity. We show that bias in photon-counting data can be corrected, even at the high count rates needed to optimize the time resolution. Using all these results, we discuss the factors that limit the time resolution of single-molecule spectroscopy and the conditions that would be needed to push measurements into the submicrosecond region.

Optimization of fast output from SiPM array for pulse shape discrimination techniques at high counting rates

Plastic scintillators with pulse shape discrimination (PSD) capability, when combined with silicon photo-multipliers (SiPMs), enable the development of compact neutron detectors with lower power consumption and insensitivity to magnetic fields. However, the SiPM array has a significantly large pulse width of the output signal, which leads to discrimination difficulties at high counting rates. There are two outputs of a SiPM array: a standard output for energy measurement and a fast output for timing measurement. The pulse width of the standard output signal is in the range of hundreds nanoseconds, while the pulse width of the other one is in the range of tens nanoseconds. Fast output signals have traditionally been considered suitably for fast timing, however utilizing them for PSD has been little explored. In our previous work, we successfully implemented PSD by using fast output signals from a SiPM. Despite the obvious negative overshoot in fast signals, we achieved PSD of fast signals by using longer sampling times. However, this approach was still limited at high counting rates. This study proposes a compensation network for fast output signals, which is composed of a compensation unit consisting of a resistor and a capacitor. This design effectively compensates the overshoot of the fast output and shortens the pulse width from 60 ns to 44 ns. Additionally, it highlights the frequency amplitude differences between the neutron and gamma signals from fast output in the high-frequency component, thus improving the PSD capability of the fast output.

Record high counting rate of a non-beam-based positron annihilation age–momentum correlation (AMOC) spectrometer achieved by geometrical optimization of detectors

Positron annihilation age–momentum correlation (AMOC) spectroscopy is not only a critical approach to investigate positronium formation and annihilation, but also a powerful technique for materials science to characterize the chemical environment of pores. However, due to the long measurement time (several days to collect 10 million counts for one sample, at a low coincidence counting rate of approximately 20–40 cps) of a conventional non-beam-based AMOC spectrometer, AMOC technique has been rarely applied. In this work, based on the geometrical simulations of detectors using Geant4 program, we developed a new semi-digital AMOC spectrometer with two start detectors. After systematic optimizations of geometrical configurations of detectors, timebase of digital oscilloscope, and the energy windows of start and stop detectors, this instrument achieved the highest coincidence counting rate for a non-beam-based AMOC spectrometer (∼ 180 cps for a narrow stop energy window of 469–589 keV and the shaping time of HPGe detector at THPGeshaping = 6μs, and ∼ 500 cps for a wide stop energy window of 104–589 keV and THPGeshaping = 2μs). The drastic rise of coincidence counting rate will broaden the applications of AMOC spectrometers in positronium physics and materials characterization in future.

Aging suppression in Multistrip Multigap Resistive Plate Chambers for high counting rate experiments

A long term operation of Multi-Strip Multi-Gap Resistive Plate Chambers (MSMGRPC) with gas mixtures based on C2H2F4 and SF6 leads to aging effects observed as depositions on the surface of the resistive electrodes, especially in the region of the spacers used for defining the gas gaps between the resistive electrodes. The observed higher noise rate and dark current has a negative impact on the performance of the chamber and leads to an increase of the data volume in a free running readout mode operation. MSMGRPC prototypes designed with a direct gas flow through the gas gaps and minimization of the number of spacers in the active area were developed as mitigation solution. Three new prototypes of different granularities were assembled using fishing line as spacers and investigated for aging effects. Although a significant reduction in the dark current and dark counting rate was evidenced, noise rate localized around the fishing line spacers, even though reduced, still remains. In this paper, a new generation of direct flow chambers based on discrete spacers is presented. The results of their aging investigations show that, even at lower gas flows, the aging effects become negligible.