PMT Output Research Articles

Investigating the large signal phenomenon in single photo-electron measurements of the 20-inch MCP-PMT

In this paper, we investigated a large signal phenomenon (LSP) in single photo- electron (SPE) measurement of the 20-inch MCP-PMT. The LSP will cause a long tail of the PMT output charge spectrum, and it will affect the calculation of the number of photoelectrons (PEs) collected and the gain of the PMT. To evaluate the LSP of the 20-inch MCP-PMT, a parameterization method is developed, by measurement of the LSP distribution in the full photocathode of the PMT and study of LSP variation with different voltage ratios applied for the PMT.

A portable and high-sensitivity optical sensing system for detecting fluorescently labeled enterohaemorrhagic Escherichia coli Shiga toxin 2B-subunit.

We developed a stand-alone, real-time optical detection device capable of reading fluorescence intensities from cell samples with high sensitivity and precision, for use as a portable fluorescent sensor for sensing fluorescently labeled enterohemorrhagic Escherichia coli (EHEC) Shiga toxins (Stxs). In general, the signal intensity from the fluorescently labeled Stxs was weak due to the small number of molecules bound to each cell. To address this technical challenge, we used a highly sensitive light detector (photomultiplier tube: PMT) to measure fluorescence, and designed a portable optical housing to align optical parts precisely; the housing itself was fabricated on a 3D printer. In addition, an electric circuit that amplified PMT output was designed and integrated into the system. The system shows the toxin concentration in the sample on a liquid crystal display (LCD), and a microcontroller circuit is used to read PMT output, process data, and display results. In contrast to other portable fluorescent detectors, the system works alone, without any peripheral computer or additional apparatus; its total size is about 17 × 13 × 9 cm3, and it weighs about 770 g. The detection limit was 0.01 ppm of Alexa Fluor 488 in PBS, which is ten thousand times lower than those of other smartphone-based systems and sufficiently sensitive for use with a portable optical detector. We used the portable real-time optical sensing system to detect Alexa Fluor 488–tagged Stx2B-subunits bound to monocytic THP-1 cells expressing the toxin receptor globotriaosylceramide (Gb3). The device did not detect a signal from Gb3-negative PD36 cells, indicating that it was capable of specifically detecting Stxs bound to cells expressing the toxin receptor. Following the development of a rapid and autonomous method for fluorescently tagging cells in food samples, the optical detection system described here could be used for direct detection of Shiga toxins in food in the field.

Rapid Characterization of Biomolecules\u2019 Thermal Stability in a Segmented Flow-Through Optofluidic Microsystem

Optofluidic devices combining optics and microfluidics have recently attracted attention for biomolecular analysis due to their high detection sensitivity. Here, we show a silicon chip with tubular microchannels buried inside the substrate featuring temperature gradient (∇T) along the microchannel. We set up an optical fluorescence system consisting of a power-modulated laser light source of 470 nm coupled to the microchannel serving as a light guide via optical fiber. Fluorescence was detected on the other side of the microchannel using a photomultiplier tube connected to an optical fiber via a fluorescein isothiocyanate filter. The PMT output was connected to a lock-in amplifier for signal processing. We performed a melting curve analysis of a short dsDNA – SYBR Green I complex with a known melting temperature (TM) in a flow-through configuration without gradient to verify the functionality of the proposed detection system. We then used the segmented flow configuration and measured the fluorescence amplitude of a droplet exposed to ∇T of ≈ 2.31 °C mm−1, determining the heat transfer time as ≈ 554 ms. The proposed platform can be used as a fast and cost-effective system for performing either MCA of dsDNAs or for measuring protein unfolding for drug-screening applications.

EXCITATION OF PLASMA BY ELECTRIC PULSES IN NEON MEDIUM

We studied characteristics of the neon plasma source excited in the atmosphere under the following conditions: gas pressure is about 2 Torr, rectangular pulses have an amplitude from 200 to 800 V, pulse duration is from 0.2 to 10 μs, repetition rate is from 0.2 up to 1 kHz. There is a mode with a stable and unstable mode of existence of the plasma when the voltage on the electrodes of the plasma source varies from 800 to 350 V and from 350 to 250 V before the extinction of the plasma. The pulse from the PMT output in a steady state plasma has a decay of about 100 μs, the duration of which does not depend on the magnitude of the voltage, frequency and pulse duration. With a decrease in the supply voltage U, the pulse front duration with a photomultiplier is increased from 74 to 450 ns. It is shown that a large neon plasma relaxation time of 100 µs compared with a beam pulse duration of 1…2 µs allows only one time to change the phase of the accelerating field.

Cryogenic R5912-20Mod photomultiplier tube characterization for the ProtoDUNE dual phase detector

The Deep Underground Neutrino Experiment (DUNE) is a dual-site experiment for long-baseline neutrino oscillation studies, and for neutrino astrophysics and nucleon decay searches. The far detector is a 40-kton underground liquid argon time-projection-chamber (LAr TPC), in which the photon detector system adds precise timing capabilities. The ProtoDUNE Dual-Phase detector will consist of a 6×6×6 m3 LAr TPC to be operated at the CERN Neutrino Platform and the photon detection system will be formed by 8-inch cryogenic photomultipliers from Hamamatsu. The PMT model (R5912-20Mod) performance at cryogenic temperature is studied including dark current, gain, and linearity with the light intensity and pulse rate. In addition, the PMT base design is validated. At cold, a decrease of the PMT amplification, or fatigue effect, is measured as the PMT output current increases, either, due to high gain, light intensity or rate. Also, the characterization results of the 40 photomultipliers to be used in ProtoDUNE Dual-Phase are presented.

Reset charge sensitive amplifier for NaI(Tl) gamma-ray spectrometer

The time constant of the output signal of the front-end readout circuit of a traditional gamma-ray spectrometer with a NaI(Tl)+PMT structure is affected by temperature, measurement environment and the signal transmission cable, so it is difficult to get a good resolution spectrum, especially at higher counting rates. In this paper, a reset charge sensitive amplifier (RCSA) is designed for the gamma-ray spectrometer with a NaI(Tl)+PMT structure. The designed RCSA outputs a step signal, thus enabling the acquisition of double-exponential signals with a stable time constant by using the next stage of a CR differentiating circuit. The designed RCSA is mainly composed of a basic amplifying circuit, a reset circuit and a dark current compensation circuit. It provides the output step signal through the integration of the PMT output charge signal. When the amplitude of the step signal exceeds a preset voltage threshold, it triggers the reset circuit to generate a reset pulse (about 5µs pulse width) to reset the output signal. Experimental results demonstrated that the designed RCSA achieves a charge sensitivity of 4.26×1010V/C, with a zero capacitance noise of 51.09fC and a noise slope of 1.98fC/pF. Supported by the digital shaping algorithm of the digital multi-channel analyzer (DMCA), it can maintain good energy resolution with high counting rates up to 150kcps and with a temperature range from −19°C to 50°C.

Design of the Front-End Readout Electronics for ATLAS Tile Calorimeter at the sLHC

We present a detailed design for the upgrade of the analog front-end electronics for the ATLAS Tile Calorimeter (TileCal) at the sLHC by using the latest deep-micron-technology based, commercial off-the-shelf (COTS) components. We believe that with the latest technology based analog devices, the significant improvements in radiation tolerance are possible. The front-end analog electronics presents a 17-bit dynamic range in readout of PMT signals. The PMT output signal is processed with a 7-pole passive LC shaper, followed by a pair of bi-gain amplifiers and two 40Msps sampling ADCs. The readout system is capable of measuring energy deposition in a single calorimeter cell from ∼220MeV to 1.3TeV with full digital Level-1 trigger capability for the ATLAS experiment at the sLHC. The other on-board features include slow current integrator used for detector calibration with cesium source to normalize the PMT gains and the charge injection for calibrating linearity and dynamic range for the readout electronics. A total of ∼10,000 channels of readout electronics are needed in the upgrade to replace the current system at the LHC.

Design and simulation of a novel method for determining depth-of-interaction in a PET scintillation crystal array using a single-ended readout by a multi-anode PMT

PET detectors with depth-of-interaction (DOI) encoding capability allow high spatial resolution and high sensitivity to be achieved simultaneously. To obtain DOI information from a mono-layer array of scintillation crystals using a single-ended readout, the authors devised a method based on light spreading within a crystal array and performed Monte Carlo simulations with individual scintillation photon tracking to prove the concept. A scintillation crystal array model was constructed using a grid method. Conventional grids are constructed using comb-shaped reflector strips with rectangular teeth to isolate scintillation crystals optically. However, the authors propose the use of triangularly shaped teeth, such that scintillation photons spread only in the x-direction in the upper halves of crystals and in the y-direction in lower halves. DOI positions can be estimated by considering the extent of two-dimensional light dispersion, which can be determined from the multiple anode outputs of a position-sensitive PMT placed under the crystal array. In the main simulation, a crystal block consisting of a 29 × 29 array of 1.5 mm × 1.5 mm × 20 mm crystals and a multi-anode PMT with 16 × 16 pixels were used. The effects of crystal size and non-uniform PMT output gain were also explored by simulation. The DOI resolution estimated for 1.5 × 1.5 × 20 mm3 crystals was 2.16 mm on average. Although the flood map was depth dependent, each crystal was well identified at all depths when a corner of the crystal array was irradiated with 511 keV gamma rays (peak-to-valley ratio ∼9:1). DOI resolution was better than 3 mm up to a crystal length of 28 mm with a 1.5 × 1.5 mm2 or 2.0 × 2.0 mm2 crystal surface area. The devised light-sharing method allowed excellent DOI resolutions to be obtained without the use of dual-ended readout or multiple crystal arrays.

A 4-GHz frequency-domain fluorometer with internal microchannel plate photomultiplier cross-correlation

We have developed and tested a multifrequency phase/modulation fluorometer based on the Hamamatsu Model R2024U gatable microchannel plate photomultiplier (MCP-PMT), using internal MCP-PMT cross-correlation. This internal mixing is accomplished by biasing and modulating the gating mesh which is located 0.2 mm behind the photocathode. Near the photocathode center, no high-frequency photocurrent modulation was achieved. Within a circular area near the photocathode edge, however, the R2024U allows accurate phase shift and demodulation measurements up to at least 4.5 GHz, the frequency limit of our PMT-modulation amplifier. By mixing immediately after the photocathode, there is no decrease in the time resolution due to transit time spread, and the MCP has to process only low-frequency signals. This means no low-level high-frequency signal voltages have to be handled in this fluorometer, and the problems of RF shielding become much less critical. Also, the effective output impedance of the PMT has been increased, resulting in a 43-dB increase in the PMT output signal power. In principle, more MCPs could be built into the PMT, allowing an improved fluorescence detection limit. We have used the method of reference fluorophores in order to compensate for pronounced PMT color effects, a wavelength-dependent modulation, and a wavelength-dependent time shift. No color correction is required in the case of time-dependent depolarization. The performance of the instrument was verified by measurements of the intensity decay of perylene, which showed a single-exponential decay, and by measurements of the decay of tryptophan in water, which showed a double-exponential decay, as expected. Additionally, we measured a 231-ps decay time for rose bengal in a methanol:water mixture (50:50), and a 183-ps correlation time. This method of detection and mixing could be of particular usefulness in studies of time-dependent photon migration in tissues, which require high modulation frequencies, but do not require the detector to be free of color effects.

A simple method to estimate small photoelectron numbers for a photomultiplier using the log-normal function

A very simple estimation method for the relative variance of a PMT output distribution with small photoelectron numbers, based on shifting a log-normal function in the negative direction along the x-axis, is presented. The method does not require a computer system but it still provides satisfactory results in a straightforward way without too much discrepancy from true values.