Showing papers by "Anton S. Tremsin published in 2009"

Detection efficiency, spatial and timing resolution of thermal and cold neutron counting MCP detectors

Abstract: Neutron counting detectors with boron or gadolinium doped microchannel plates (MCPs) have very high detection efficiency, spatial and temporal resolution, and have a very low readout noise. In this paper we present the results of both theoretical predictions and experimental evaluations of detection efficiency and spatial resolution measured at cold and thermal neutron beamlines. The quantum detection efficiency of a detector (not fully optimized) was measured to be 43% and 16% for the cold and thermal beamlines, respectively. The experiments also demonstrate that the spatial resolution can be better than 15 μm—highest achievable with the particular MCP pore dimension used in the experiment, although more electronics development is required in order to increase the counting rate capabilities of those

Nano-engineered ultra-high-gain microchannel plates

Abstract: Highly localized and very fast electron amplification of microchannel plates (MCPs) enables a large number of high-resolution and high-sensitivity detection technologies, which provide spatial and/or temporal information for each detected photon/electron/ion/neutron. Although there has been significant progress in photocathode and readout technologies the MCPs themselves have not evolved much from the technology developed several decades ago. Substantial increases in the gain of existing MCP technology have been accomplished by utilizing state-of-the-art processes developed for nano-engineered structures. The gain of treated MCPs with aspect ratio of 40:1 is reproducibly measured to reach unprecedented values of 2×10 5 . This gain enhancement is shown to be stable during MCP operation. In addition, the initial experiments indicate improved stability of gain as a function of extracted charge and MCP storage conditions. We also present results from a fully independent thin-film process for manufacturing non-lead glass MCPs using engineered thin films for both the resistive and emissive layers. These substrate-independent MCPs show high gain, less gain degradation with extracted charge, and greater pore-to-pore and plate-to-plate uniformity than has been possible with conventional lead glass structures.

Single-quantum dot imaging with a photon counting camera

Abstract: The expanding spectrum of applications of single-molecule fluorescence imaging ranges from fundamental in vitro studies of biomolecular activity to tracking of receptors in live cells. The success of these assays has relied on progress in organic and non-organic fluorescent probe developments as well as improvements in the sensitivity of light detectors. We describe a new type of detector developed with the specific goal of ultra-sensitive single-molecule imaging. It is a wide-field, photon-counting detector providing high temporal and high spatial resolution information for each incoming photon. It can be used as a standard low-light level camera, but also allows access to a lot more information, such as fluorescence lifetime and spatio-temporal correlations. We illustrate the single-molecule imaging performance of our current prototype using quantum dots and discuss on-going and future developments of this detector.

Microchannel plate devices with tunable resistive films

Abstract: A microchannel plate for detecting neutrons includes a hydrogen-rich polymer substrate that defines a plurality of channels extending from a top surface of the substrate to a bottom surface of the substrate, where neutrons interact with the plurality of channels to generate at least one secondary electron. A top electrode is positioned on the top surface of the substrate and a bottom electrode is positioned on the bottom surface of the substrate. A resistive layer is formed over an outer surface of the plurality of channels that provides ohmic conduction with a resistivity that is substantially constant. An emissive layer is formed over the resistive layer. Neutron interaction products interact with the plurality of channels defined by the substrate and the emissive films to generate secondary electrons that cascade within the plurality of channels to provide an amplified signal related to the detection of neutrons.

High Spatial and Temporal Resolution Neutron Imaging With Microchannel Plate Detectors

Abstract: Special microchannel plates (MCPs) developed by Nova Scientific Inc. incorporate high efficiency neutron conversion materials into the MCP to provide a high neutron stopping power. 10B and natGd have high interaction cross sections for thermal neutrons and their incorporation into MCP glass is a convenient way to make efficient MCPs for neutron detection with high spatial resolution. We have evaluated neutron event counting 2D imaging detectors using these MCPs with a cross delay line readout, cross strip readout, and a Medipix2 readout. Tests at several reactors with the cross delay line and cross strip readouts have established spatial resolution with neutrons as good as ~30 microns FWHM over a 27 mm diameter detector, with event rates approaching 1 MHz, low fixed pattern noise, event time tagging of 25 ns and intrinsic background rates of < 0.05 events cm-2 sec-1. Evaluation of neutron sensing MCP detector with Medipix2 readout (14 mm2) has allowed operation at high counting rates (500 MHz) with the spatial resolution limited by the 55 micron pixel size of the Medipix2 readout. We have also used the Medipix2 for centroiding of neutron events to sub pixel resolution to obtain better spatial resolution (< 15 mum) for neutrons at reduced event rates (100 kHz). Initial measurements of thermal neutron detection efficiencies give values of 20% to 25% for thermal neutrons and 45% for cold neutrons without optimization of the detection geometry. Preliminary tests with shielding and a LaBr scintillator to gate neutron detections in coincidence with gamma rays produced by neutron interactions has enabled gamma ray rejection factors of 3 times 104 to be achieved. Further improvements in the neutron detection efficiency and gamma ray discrimination efficiency can be gained by optimization of the geometrical and electronic configurations.

High-resolution neutron radiography with microchannel plates: Proof-of-principle experiments at PSI

Abstract: With the appearance of highly collimated and intense neutron beamlines, the resolution of radiographic experiments is often limited by the parameters of the neutron imaging detector. Neutron-sensitive microchannel plates (MCPs) proved to be very efficient for conversion of a thermal or cold neutron into an electron pulse of up to 106 electrons preserving location of the neutron absorption within ∼15 μm. In this paper, we present the results of preliminary measurements performed with neutron-sensitive MCPs coupled with a Medipix2/Timepix active pixel sensor. A set of test objects was imaged at both thermal and cold neutron imaging beamlines of Paul Scherrer Institute. The spatial resolution of the detector operating at high counting rate mode was confirmed to be limited by the 55 μm pixel size of the Medipix2 readout. At the same time, event centroiding applied to the charge values measured with Timepix readout allowed individual neutron counting with spatial resolution on the scale of MCP pore spacing (11 μm in the present measurements). The ongoing improvement of the speed of the readout electronics should eliminate the low counting rate limitation of the latter high-resolution imaging.

Microchannel plate cross-strip detectors with high spatial and temporal resolution

Abstract: The cross-strip imaging readout employs charge division, and centroiding, of microchannel plate charge signals detected on two orthogonal layers of sense strips to encode event X–Y positions and times. We have developed cross-strip detectors and fully parallel channel position encoding electronics. The front-end amplifiers utilize two 32-channel pre-amplifier ASICs that send signals to a full 64-channel 60 MHz ADC circuit followed by a FPGA event-processing board. Tests with a software Finite Impulse Response filter and centroiding algorithm demonstrate 1 MHz in combination with firmware-based FPGA centroiding algorithms.

Energy-Resolving Neutron Transmission Radiography at the ISIS Pulsed Spallation Source With a High-Resolution Neutron Counting Detector

Abstract: Neutron transmission radiography can be strongly enhanced by adding spectroscopic data spatially correlated with the attenuation coefficient. This can now be achieved at pulsed neutron sources, utilizing a neutron detector with high spatial and temporal resolution. The energy of transmitted neutrons can be recovered from their time-of-flight, simultaneously with the acquisition of the transmission radiographic image by a pixelated detector. From this, the positions of Bragg edges can be obtained for each pixel of the radiographic image. The combination of both spectroscopic and transmission information enables high spatial resolution studies to be carried out on material composition, phase transitions, texture variations, as well as strain analysis, as long as the resolution and statistics are favorable. This paper presents initial results from proof-of-principle experiments on energy-resolved neutron transmission radiography, using a neutron counting detector consisting of neutron-sensitive microchannel plates (MCPs) and a Medipix2 electronic readout. These experiments demonstrate that the position of Bragg edges are measurable with a few mAring resolution in each 55-mum pixel of the detector, corresponding to DeltaE/E~0.1%. However, the limited intensity of most current neutron sources requires a compromise between the energy resolution and the area over which it was integrated. Still, the latter limitation can be overcome by combining energy information for several neighboring pixels, while transmission radiography can still be done at the limit of the detector spatial resolution.

The current and future capabilities of MCP based UV detectors

Abstract: At the heart of future space-based astronomical UV instruments will be a sensitive UV detector. Though there has been a death of new UV mission opportunities, detector development has continued. Improvements have been made in spatial resolution, dynamic range, detector size, quantum efficiency and background. At the same time the power and mass required to achieve these goals have decreased. We review the current capabilities of microchannel plate based detectors at Berkeley, both in the laboratory and aboard current on-orbit spacecraft. We also discuss what can be expected from the next generation of UV detectors over the next decade.

Development of cross strip MCP detectors for UV and optical instruments

Abstract: Microchannel plate detectors with cross strip anodes have demonstrated excellent performance characteristics, their resolution has reached the 6-10 μm scale (the typical size of pores in a microchannel plate) and the imaging nonlinearities are small. Working at much lower gain (~5 x 10 5 ) than many other devices, the cross strip readout has many other advantages, low complexity, robustness, compactness and the ability to fit many formats. We have now implemented cross strip detectors in several formats including, 40mm open face (UV/particle) and 18mm sealed tube (optical). These have been combined with a new signal processing technique which allows for high counting rates exceeding 5 MHz with high spatial resolution (<20 μm FWHM). The imaging performance is dependent on optimization of firmware algorithms that are used to calculate event position centroids. With new FPGA designs and implementation considerable flexibility is gained, allowing the fidelity of the imaging readout to be progressively tuned for maximal performance.

Microchannel plate devices with multiple emissive layers

Abstract: A microchannel plate includes a substrate defining a plurality of pores extending from a top surface of the substrate to a bottom surface of the substrate. The plurality of pores includes a resistive material on an outer surface that forms a first emissive layer. A second emissive layer is formed over the first emissive layer. The second emissive layer is chosen to achieve at least one of an increase in secondary electron emission efficiency and a decrease in gain degradation as a function of time. A top electrode is positioned on the top surface of the substrate and a bottom electrode is positioned on the bottom surface of the substrate.

Phasor-based single-molecule fluorescence lifetime imaging using a wide-field photon-counting detector

Abstract: Fluorescence lifetime imaging (FLIM) is a powerful approach to studying the immediate environment of molecules. For example, it is used in biology to study changes in the chemical environment, or to study binding processes, aggregation, and conformational changes by measuring Forster resonance energy transfer (FRET) between donor and acceptor fluorophores. FLIM can be acquired by time-domain measurements (time-correlated single-photon counting) or frequency-domain measurements (with PMT modulation or digital frequency domain acquisition) in a confocal setup, or with wide-field systems (using time-gated cameras). In the best cases, the resulting data is analyzed in terms of multicomponent fluorescence lifetime decays with demanding requirements in terms of signal level (and therefore limited frame rate). Recently, the phasor approach has been proposed as a powerful alternative for fluorescence lifetime analysis of FLIM, ensemble, and single-molecule experiments. Here we discuss the advantages of combining phasor analysis with a new type of FLIM acquisition hardware presented previously, consisting of a high temporal and spatial resolution wide-field single-photon counting device (the H33D detector). Experimental data with live cells and quantum dots will be presented as an illustration of this new approach.

High Speed Multichannel Charge Sensitive Data Acquisition System With Self-Triggered Event Timing

Abstract: A number of modern experiments require simultaneous measurement of charges on multiple channels at > MHz event rates with an accuracy of 100-1000 e- mis. One widely used data processing scheme relies on application of specific integrated circuits enabling multichannel analog peak detection asserted by an external trigger followed by a serial/sparsified readout. Although this configuration minimizes the back end electronics, its counting rate capability is limited by the speed of the serial readout. Recent advances in analog to digital converters and FPGA devices enable fully parallel high speed multichannel data processing with digital peak detection enhanced by finite impulse response filtering. Not only can accurate charge values be obtained at high event rates, but the timing of the event on each channel can also be determined with high accuracy. We present the concept and first experimental tests of fully parallel 128-channel charge sensitive data processing electronics capable of measuring charges with an accuracy of ~1000 e- rms. Our system does not require an external trigger and, in addition to charge values, it provides the event timing with an accuracy of ~1 ns FWHM. One of the possible applications of this system is high resolution position sensitive event counting detectors with microchannel plates combined with cross strip readout. Implementation of fast data acquisition electronics increases the counting rates of those detectors to multi-MHz level, preserving their unique capability of virtually noiseless detection of both position (with an accuracy of ~10 mum FWHM) and timing (~1 ns FWHM) of individual particles, including photons, electrons, ions, neutrals, and neutrons.

Direct deposition of GaN-based photocathodes on microchannel plates

Abstract: Epitaxial growth of p-type GaN-based UV photocathode by RF plasma assisted molecular beam epitaxy (MBE) on sapphire, fused silica, and alumina substrates was investigated. The electrical measurements indicted the growth of highly p-type GaN films as thin as 0.1 μm on c-plane sapphire with a thin AlN nucleation layer. Polycrystalline p-type GaN was obtained for growth on fused silica and alumina. Negative electron affinity (NEA) photocathodes were fabricated by cesium activation of the p-type GaN films in vacuum. Quantum efficiency for UV detection on different substrates was then characterized. To study the integration of UV photocathodes with MCPs, direct deposition of p-type GaN films on glass MCPs were done at low growth temperatures by MBE. The detection efficiency of polycrystalline p- GaN photocathodes in reflection mode was much less than the high quality p-type GaN films on sapphire, however, it was comparable to the detection efficiency of the latter measured in the semitransparent mode. This indicates the potential for fabrication of improved photocathodes with higher gain and better spatial and temporal resolutions.

Image intensifying device

Abstract: An image intensifying device includes a lens that is positioned at a light input that forms an image of a scene The image intensifying device also includes an image intensifier tube that includes a photocathode that is positioned to receive the image formed by the lens The photocathode generates photoelectrons in response to the light image of the scene The image intensifier tube also includes a microchannel plate having an input surface comprising the photocathode The microchannel plate receives the photoelectrons generated by the photocathode and generating secondary electrons An electron detector receives the secondary electrons generated by the microchannel plate and generates an intensified image of the scene

Novel fast neutron counting technology for efficient detection of special nuclear materials

Abstract: Results from a fully independent thin film process for manufacturing non-lead glass Microchannel plate (MCP) detectors using nano-engineered thin films for both the resistive and emissive layers are presented. These novel MCP devices show high gain, less gain degradation with extracted charge, and greater pore to pore and plate to plate uniformity than has been possible with conventional lead glass structures. Extension of MCP to plastic substrates, for the purpose of fast neutron detection is disclosed and preliminary MCP functionality results are presented. Simulation results, predicting fast neutron detection performance for the plastic MCP device are presented and discussed

High resolution stroboscopic neutron radiography at the FRM-II ANTARES facility

Abstract: The rapidly developing field of high resolution neutron radiography primarily concentrates on non-destructive studies of stationary objects with relatively long exposure times required to achieve adequate neutron statistics. The combination of a high intensity neutron beam with a high temporal and spatial resolution detector, enables the investigation of dynamic processes in a stroboscopic mode, where image frames are synchronized with the sample or acquired continuously at high acquisition frame rates. Although neutron statistics in the acquisition frames as short as <10 μs is considered quite low (typically <1000 n/cm2 at the sample), repetitive processes can still be studied with high resolution by integrating a large number of frames synchronized to the process. In this paper we demonstrate the stroboscopic imaging capabilities of the highly collimated thermal neutron beamline ANTARES together with a high resolution detector with neutron sensitive microchannel plates and the Medipix2 readout. The dynamics of water uptake due to capillary forces as well as the two-phase flow of an air-water mixture is investigated, and stroboscopic imaging of an operating beam chopper and a spinning fan is performed, with sub-100 μm spatial resolution and with acquisition frames varying between 10 μs and 200 ms. The results of these experiments demonstrate the future potential for performing high resolution neutron radiography of fast and/or repetitive processes, such as water flow and uptake, operation of fuel injection nozzles, as well as many others.

Image intensifying device having a microchannel plate with a resistive film for suppressing the generation of ions

Abstract: An image intensifying device includes a lens that is positioned at a light input that forms an image of a scene. The image intensifying device also includes an image intensifier tube that includes a photocathode that is positioned to receive the image formed by the lens. The photocathode generates photoelectrons in response to the light image of the scene. The image intensifier tube also includes a microchannel plate having an input surface comprising the photocathode. The microchannel plate receives the photoelectrons generated by the photocathode and generating secondary electrons. An electron detector receives the secondary electrons generated by the microchannel plate and generates an intensified image of the scene.

A design for large-area fast photo-detectors with transmission-line readout and waveform sampling

Abstract: We present a preliminary design and the results of simulation for a photo-detector module to be used in applications requiring the coverage of areas of many square meters with time resolutions less than 10 picoseconds and position resolutions of less than a millimeter for charged particles. The source of light is Cherenkov light in a radiator/window; the amplification is provided by panels of micro-pores functionalized to act as microchannel plates (MCPs). The good time and position resolution stems from the use of an array of parallel 50 Ω transmission lines (strips) as the collecting anodes. The anode strips feed multi-GS/sec sampling chips which digitize the pulse waveform at each end of the strip, allowing a measurement of the time from the average of the two ends, and a 2-dimensional position measurement from the difference of times on a strip, and, in the orthogonal direction, the strip number, or a centroid of the charges deposited on adjacent strips. The module design is constructed so that large areas can be ‘tiled’ by an array of modules

Procédé de fabrication de dispositifs de plaques à microcanaux avec plusieurs couches émissives

Abstract: Cette invention concerne un procede de fabrication d’une plaque a microcanaux comprenant la definition de plusieurs pores partant d’une surface superieure d’un substrat vers une surface inferieure du substrat, les multiples pores comportant un materiau resistif sur une surface exterieure qui forme une premiere couche emissive. Une seconde couche emissive est formee par-dessus la premiere couche emissive. La seconde couche emissive est choisie de maniere a obtenir au moins une augmentation de l’efficacite d’emission electronique secondaire et une diminution de la baisse de gain en fonction du temps. Une electrode superieure est formee sur la surface superieure du substrat et une electrode inferieure sur la surface inferieure du substrat.