One of the key components of a time-of-flight (TOF) spectrometer is the detection system. In addition to high timing resolution, accurate two-dimensional imaging substantially broadens the areas of applications of TOF spectrometers; for example, add a new dimension to angle-resolved photoemission spectroscopy (ARPES). In this paper we report on the recent developments of a high spatial (<50 mm) and timing (<130 ps) resolution imaging system capable of selective detection of electrons, ions and/or photons. Relative to our previously reported results, we have substantially improved the counting rate capabilities of the system especially for cases where the energy range of interest represents a small fraction of the incoming flux at the detector plane. The new system ignores all the events outside of a tunable time window substantially decreasing the dead time required for the event processing. That allows high-resolution TOF measurements within a given energy or momentum range and also can be used for distinguishing (or disabling) detection of photons versus detection of charged particles. The counting rate within a given energy window can be as high as ~;;400KHz at 10percent dead time. The electron detection system reported in the paper was developed for the TOF ARPES experiments at the Advanced Light Source, Lawrence Berkeley National Laboratory.

Microchannel plate (MCP) event-counting imaging detectors with very high spatial resolution (~10 µm) and timing accuracy (~100 ps) are widely employed for the detection and imaging applications of electrons and ions, as well as UV and X-ray photons. Recently it was demonstrated that the many advantages of MCPs are also applicable to neutron detection with high 2-dimensional spatial resolution. Boron, enriched in the isotope 10B, was added to the MCP glass structure to enhance the neutron interaction within the MCP through the 10B(n,?)7Li reaction. The energetic charged particle reaction products release secondary electrons directly into MCP channels, initiating an electron avalanche and a subsequent strong output pulse. In this paper we present a detailed model for calculating the quantum detection efficiency of MCP neutron detectors incorporating 10B, for the specific case of square channel MCP geometry. This model predicts that for thermal neutrons (0.025 eV), MCP detection efficiencies of up to 78% are possible using square channels. We also show theoretically that square channel MCPs should have a very sharp (~ 17 mrad) angular drop in sensitivity for detection of normal incidence neutrons, opening up new possibilities for angle-sensitive neutron imaging as well as collimation. The calculations can be used to optimize MCP neutron detection efficiency for a variety of applications. In a subsequent companion paper, the model will be extended to the case of hexagonally-packed circular channels.

The absolute quantum efficiency of polycrystalline diamond films grown on silicon substrates by chemical vapor deposition (CVD) is reported in the range of 25-200 nm. The efficiency of boron-doped and hydrogen-activated by microwave plasma reflective photocathodes peaked at 37% at 40 nm with the sensitivity cutoff observed at similar to190 nm. We confirmed that hydrogen activation is relatively stable in air: the efficiency of the photocathode degraded by less than 15% after an 18-h air exposure. It was found that diamond photocathodes can be reactivated multiple times to the same high QE values even after extended ultrasonic cleaning in both water and alcohol. The sensitivity of a diamond photocathode coated with a high dipole moment 4-nm-thick CsI layer was found to be slightly better than that of hydrogenated films, especially at longer wavelengths, while the sensitivity cutoff shifted to similar to200 nm. The observed high efficiency of thin CVD diamond films and relatively high stability of surface activation makes them a very attractive alternative to many existing UV photocathodes, especially taking into account other useful features of diamond (mechanical and chemical stability and radiation hardness). (C) 2004 Elsevier B.V. All rights reserved.

A novel type of thermal and cold neutron collimator based on microchannel plates (MCPs) doped with neutron-absorbing atoms is discussed. In contrast to widely used Soller slit collimators, the MCPs collimate a beam of neutrons in two dimensions simultaneously and they are very compact. A detailed model of the circular-pore MCP collimator performance, described in this paper, can be used for optimization of MCP parameters in order to achieve the most efficient collimation for a given application. Among these parameters are the MCP geometrical dimensions, the type of absorbing atoms and their concentration in the MCP glass mixture, all constrained by the manufacturing limitations. The model predicts that the MCP collimators can be very efficient (rocking curve < 0.1 degrees wide with high background suppression in the wings) and very compact (only a few mm thick). In addition to collimation, the same MCPs can also be used for neutron imaging with a high spatial (~20 um) and temporal (~1 microsecond) resolution, opening up new possibilities for simultaneous beam collimation and monitoring. (c) 2005 Elsevier B.V. All rights reserved.

Recent advances in the photon counting, imaging readout for microchannel plate (MCP) detectors has led to a substantial improvement in their spatial resolution. The spatial accuracy (similar to 7-10 um) of an MCP detector with a cross strip (XS) readout has been shown to be limited by the MCP pore size (< 10 um). In this paper, we study the ultimate resolution limits of the XS readout itself. The model allows us to determine the requirements on the anode's geometry and the signal processing electronics in order to reach a particular spatial resolution. The optimal detector parameters, such as the width of the charge footprint at the anode (determined by the distance and the field between the MCP and the anode), and the gain of the detector can also be found with the help of our model. The model indicates that the optimum full-width at half-maximum of the charge footprint distribution at the anode is a factor of -1.6 larger than the anode period. Given a noise of charge sensitive amplifiers of 350 electrons rms each we predict that the MCP gain can be as low as 2.5 x 10(5) for this detector to resolve similar to 7 um features.

Results of our modeling also indicate that the accuracy of the position obtained for center of gravity centroiding of the charge distribution is inferior to fitting a Gaussian-like analytical function, providing the geometry of the anode is accurate enough. The model predictions are compared with the experimentally measured images and reveal the critical parameters (anode's geometric accuracy and amplifier noise), which can be improved in future detectors.

Microchannel plate (MCP) event-counting imaging detectors with very high spatial resolution (~10 um) and timing accuracy (~100 ps) are widely employed for the detection and imaging applications of electrons and ions, as well as UV and X-ray photons. Recently, it was demonstrated that the many advantages of MCPs are also applicable to neutron detection with high two-dimensional spatial resolution. Boron, enriched in the isotope B-10, was added to the MCP glass structure to enhance the neutron interaction within the MCP through the B-10(n, alpha)(7) Li reaction. The energetic charged particle reaction products release secondary electrons directly into MCP channels, initiating an electron avalanche and a subsequent strong output pulse. In this paper we present a detailed model for calculating the quantum detection efficiency of MCP neutron detectors incorporating 10B, for the specific case of square channel MCP geometry. This model predicts that for thermal neutrons (0.025 eV), MCP detection efficiencies of up to 78% are possible using square channels. We also show theoretically that square channel MCPs should have a very sharp (similar to17 mrad) angular drop in sensitivity for detection of normal incidence neutrons, opening up new possibilities for angle-sensitive neutron imaging as well as collimation. The calculations can be used to optimize MCP neutron detection efficiency for a variety of applications. In a subsequent companion paper, the model will be extended to the case of hexagonally packed circular channels. (C) 2004 Elsevier B.V. All rights reserved.

Detectors with microchannel plates (MCPs) are currently widely used in photon and charged particle detection with high spatial (similar to 10 um) and temporal (< 0.5 ns) resolution. All the advances in MCP detection technologies can be successfully implemented for the detection of thermal neutrons by using MCPs manufactured from a modified glass mixture doped with neutron absorbing atoms. In this paper, we compare the efficiency of thermal neutron detection for two standard MCP geometries: circular-pore and square-pore MCPs doped with the B-10 isotope. The results of our modeling indicate that the detection of thermal neutrons with a square-pore MCP is 11%-23% more efficient than for the circular geometry, and can be higher than 70% for the existing MCP technology.

The same MCPs can be used as very efficient and compact thermal neutron collimators. In this paper, we compare the efficiency of circular- and square-pore MCP collimators with the help of our model, the validity of which has already been verified by our experimental measurements reported last year. The rocking curve of 5-mm and 2.5-mm thick MCPs doped with 3 mole % of (nat)Gd2O3 is predicted to be only +/- 0.1 degrees and +/- 0.3 degrees wide, respectively, for both geometries. A very compact device with high thermal neutron detection efficiency and angular sensitivity can be built by combining an MCP neutron detector with an MCP collimator.

The combination of a photocathode, microchannel plate stack and photon counting, imaging readout provides a powerful tool for high dynamic range, high spatial resolution, and high timing accuracy detectors for the X-ray to visible light spectral range. Significant improvements in spatial resolution, quantum efficiency, and background rate have made these devices attractive for many applications and are being applied to completely new research areas. We describe the latest developments in high-resolution cross-strip (XS) anode readout for photon counting imaging with microchannel plates (MCPs). We show that the spatial resolution of an MCP detector with the cross-strip readout is now limited only by the MCP pore width. For the first time, we show images of resolution test masks illustrating the exceptional spatial resolution of the cross-strip readout, which at the present time can resolve features on the scale of similar to7 mum with MCP gains as low as 6 x 10(5). Low-gain operation of the detector with high spatial resolution shown in this paper is very beneficial for applications with high local counting rate and long lifetime requirements. The spatial resolution of the XS anode can be increased even further with improved anode uniformity, lower noise front-end electronics, and new centroiding algorithms. This could be important when MCPs with smaller than existing 6 mum pores become commercially available, thus improving the detector resolution down to the few micrometer scale.

Micromachined silica microchannel plates (MCPs) under development have a number of advantages over standard glass MCPs and open completely new possibilities in detector technologies. In this article we present the results of our studies on the thermal properties of silica microchannel plates (sMCPs). Similar to standard glass microchanel plates the resistance of silica MCPs was measured to change exponentially with temperature with a negative thermal coefficient of -0.036 per degreesC, somewhat larger than that of standard glass MCPs. The resistance also decreases linearly with the applied voltage, with the voltage coefficient of -3.1x10(-4) V-1. With the knowledge of these two coefficients, our thermal model allows the calculation of the maximum voltage, which can be applied to a given MCP without inducing a thermal runaway. A typical 25 mm diam, 240 mum thick sMCP with 6 mum pores has to have the resistance larger than similar to30 MOmega to operate safely at voltages up to 800 V. With this model we can also calculate the time required for a given silica MCP to reach the point of thermal equilibrium after a voltage increase. We hope that the ongoing efforts on a proper modification of the sMCP semiconducting layer will lead to the production of new MCPs with a small negative or even a positive thermal coefficient, reducing the possibility of thermal runaways of low-resistance MCPs required for high count rate applications. (C) 2004 American Institute of Physics.