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A novel small field of view Hybrid Gamma Camera (HGC) has been developed to facilitate the process of localizing radiopharmaceutical uptake during surgical procedures. The HGC is a scintillator-based detector consisting of an electron multiplying charge-coupled device coupled to a columnar scintillator (CsI[Tl]). This enables fusion scintigraphic and optical images offering new possibilities for assisting clinicians and surgeons in localising the site of uptake in a number of surgical procedures. This technology also offers bedside imaging for small organs in procedures such as thyroid scintigraphy. In this study, prototype anthropomorphic phantoms have been used to study the capability of the HGC. Images were acquired using a range of bespoke anthropomorphic phantoms. The gamma and hybrid optical images were acquired for the simulated sentinel lymph nodes and thyroid gland. The gamma images produced varied in terms of spatial resolution and detectability, however utilizing pinhole collimators of difference diameters (0.5 and 1.0mm) imaging was enhanced meeting the needs of small field gamma imaging. The hybrid images obtained demonstrated that the HGC is ideally suited for small organ imaging demonstrating good potential in clinical procedures, such as thyroid scintigraphy, when using acquisition times similar to those for conventional gamma imaging. Moreover, clinical scintigraphic images, from patients attending the nuclear medicine clinic, were acquired using the HGC and compared to images from a standard gamma camera. The results of our first clinical feasibility study using the HGC will be presented.

We report on the performance of 6 micrometer pore diameter Microchannel Plates (MCPs) fabricated in 50 X 50 mm2 format, from both standard and radio-isotope free low noise glass, by Photonis SAS for a European Space Agency Technology Research Program. We compare them to MCPs manufactured by Photonis (the former Philips Photonics) for the High Resolution Camera (HRC) on NASA's Chandra X-ray observatory. The new MCPs represent a significant advance in MCP technology, having a much larger area than previously reported 6 micrometer plates, and demonstrating low noise 6 micrometer technology for the first time. The 6 micrometer plates are shown to be, mechanically, exceptionally well made with a defect density reduced by a factor of 2 - 5 compared to samples from the HRC flight blocks. They exhibit excellent gain and the expected 0.28 keV (Carbon K) X-ray quantum efficiency. The low noise plates have a very uniform response to X-rays but the standard glass MCPs do show inhomogeneity on both the global and multifiber scales.

In this paper we present and compare flight results with the latest results of the ground calibration for the HRC-I detector. In particular we will compare ground and in flight data on detector background, effective area, quantum efficiency and point spread response function.

The High Resolution Camera (HRC) is one of two focal plane instruments on the NASA Chandra X-ray Observatory which was successfully launched on July 23, 1999. The Chandra X-ray Observatory was designed to perform high resolution spectroscopy and imaging in the X-ray band of 0.07 to 10 keV. The HRC instrument consists of two detectors, HRC-I for imaging and HRC-S for spectroscopy. Each HRC detector consists of a thin aluminized polyimide blocking filter, a chevron pair of microchannel plates and a crossed grid charge readout. The HRC-I is an approximately 100 X 100 mm detector optimized for high resolution imaging and timing, the HRC-S is an approximately 20 X 300 detector optimized to function as the readout for the Low Energy Transmission Grating. In this paper we discuss the in-flight performance of the HRC-S, and present preliminary analysis of flight calibration data and compare it with the results of the ground calibration and pre-flight predictions. In particular we will compare ground data and in-flight data on detector background, quantum efficiency, spatial resolution, pulse height resolution, and point spread response function.

Two identical CsI-coated, low noise microchannel plate (MCP) detectors were taken to the Daresbury Synchrotron Radiation Source (SRS) to measure their quantum efficiencies over two different energy ranges - 450 eV to 1200 eV and 4.5 eV to 9.5 eV. The SRS was run in low ring current with the beam flux monitored using single wire gas proportional counters. We present accurate measurements of edge-related absolute quantum efficiency features due to the CsI photocathodes. This data will be incorporated into the calibration program of the Advanced X-ray Astrophysical Facility High Resolution Camera.

The high resolution camera (HRC) will be one of the two focal plane instruments on the Advanced X-ray Astrophysics Facility, (AXAF). AXAF will perform high resolution spectrometry and imaging in the X-ray band of 0.1 to 10 keV. The HRC instrument consists of two detectors, the HRC-I for imaging and the HRC-S for spectroscopy. Each HRC detector consists of a thin aluminized polyimide window, a chevron pair of microchannel plates (MCPs) and a crossed grid charge readout. The HRC-I is a 100 by 100 mm detector optimized for high resolution imaging and timing, the HRC-S is an approximately 30 by 300 mm detector optimized to function as the readout for the low energy transmission grating spectrometer (LETGS). In this paper we present the absolute quantum efficiency, spatial resolution, point spread response function and count rate linearity of the HRC-I detector. Data taken at the HRC laboratory and at the Marshall Space Flight Center X-ray Calibration Facility are presented. The development of the HRC is a collaborative effort between The Smithsonian Astrophysical Observatory, University of Leicester UK and the Osservatorio Astronomico, G.S. Vaiana, Palermo Italy.

The high resolution camera (HRC) is one of two focal plane detector systems that will be flown on the Advanced X-ray Astrophysics Facility (AXAF). The HRC consists of two microchannel plate (MCP) detectors: one to provide large area, high position resolution imaging and timing (HRC-I), and a second (HRC-S) to provide a readout for the AXAF low energy transmission gratings. Each detector is composed of a chevron pair of CsI coated MCPs with a crossed grid charge detector and an Al/polyimide UV/ion shield. In this paper, we describe the operation, performance and calibration of the spectroscopic detector. In particular, we discuss the absolute quantum efficiency calibration, the point spread function of the instrument combined with the AXAF telescope, the count rate linearity, the spatial linearity, and the internal background of the instrument. Data taken in the laboratory and at the x-ray Calibration Facility at Marshall Space Flight Center are presented.

The high resolution camera (HRC) is a microchannel plate based imaging detector for the Advanced X-Ray Astrophysics Facility (AXAF) that will be placed in a high earth orbit scheduled for launch in August, 1998. An end-to-end calibration of the HRC and the AXAF high resolution mirror assembly (HRMA) was carried out at the Marshall Space Flight Center's X-Ray Calibration Facility (XRCF). This activity was followed by several modifications to the HRC to improve its performance, and a series of flat field calibrations. In this paper, and the following companion papers, we discuss the calibration plans, sequences, and results of these tests. At the time of this conference, the HRC has been fully flight qualified and is being integrated into the science instrument module (SIM) in preparation for integration into the AXAF spacecraft.

We discuss the current status of the Advanced X-ray Astrophysics Facility (AXAF) High Resolution Camera (HRC) quantum efficiency (QE) calibration. The absolute quantum efficiency of flight candidate, CsI coated HRC microchannel plates (MCPs) for the imaging detector (HRC-I) manufactured by Galileo Electro-Optics Corporation (GEOC) has been measured at several energies. We find the absolute QE of these MCPs (measured at SAO) to be 0.41 at C Kalpha (E equals 277 eV) and 0.28 at Al Kalpha (E equals 1487) eV). The absolute QE of flight-like HRC-I MCPs manufactured by Phillips Components (measured at the University of Leicester) is approximately 0.40 at both C Kalpha and Si Kalpha (E equals 1739 eV). We are now in the process of measuring the absolute QE of both the HRC-I and HRC-S flight detectors at 22 different energies at 4 azimuthal and 5 polar angles. A summary of planned measurements is presented. In addition, we present data taken at the Daresbury Synchrotron Radiation Source to map out the detailed edge structure of the MCP glass and coatings. In particular, we present measurements of the relative QE of CsI coated MCPs around Cs and I M edges, and absolute measurements around the K K and Cs LIII edges. The absolute measurements of the flight instrument at the 22 discrete energies will be combined with the relative synchrotron measurements of flight-like detectors to produce the absolute QE of the HRC over the entire AXAF bandpass (0.1 to 10 keV).© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Reducing plate resistance is one of the possible ways to increase the count rate capability of microchannel plates (MCPs). Bonding a low-resistance plate to a cooled substrate provides a conductive path for heat transport an prevents thermal runaway. MCPs of very low resistance (less than or equal to 500 k(Omega) ), bonded to a Peltier cooler, were tested using different bonding techniques. Stable, reproducible operation of a rear-cooled MCP (60:1, 10 micrometer channels) was achieved for biases up to 1320 volts (RMCP equals 260 k(Omega) at that voltage), when the MCP bias current was as high as 5.1 mA and the heat generated by the plate was 0.78 W cm-2. The count rate reached the value of 108 cm-2s-1 limited not by the plate recharge time, but by the intensity of the mercury vapor UV lamp (2540 angstrom) used for illumination. The dark noise, at the same time, was less than 1 cm-2s-1. A thermal model of such conductively cooled MCPs is described. The count rate characteristic of a microchannel plate is well-known to depend on the pattern of illumination. This paper updates our previous investigation of radial gain depression in the vicinity of high count rate point-like illumination.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Soft x-ray optics based on slumped, profiled microchannel plates (MCPs) are under development. Their purpose is to collimate the expanding beam from a laser-plasma x-ray source, resulting in a parallel beam suitable for lithography of semiconductor devices. We present a prototype design for such an optic with a radius of curvature optimized for maximum beam intensity. The plate thickness (and hence the channel length) is varied as a function of distance from the plate center. The resulting plate profile is determined by the radius of curvature but not by the x- ray energy. This design is shown by Monte Carlo ray-trace modeling to give a circular illuminated field with a diameter of 36mm for 1 keV x-rays. The calculated intensity of the beam is equivalent to that of the divergence beam at a distance of 0.35m from the source. We also present preliminary x-ray measurements from the optic. These optics, while designed with the semiconductor industry in mind, may find application in any field where a uniform or parallel soft x-ray or VUV beam is required.

Microsphere plates (MSPs), a new type of electron multiplier, consisting of sintered disks of glass beads, have recently become available from El-Mul Technologies Ltd. The principles of MSP operation are similar to those of microchannel plates (MCPs). This paper reports a survey of the gain, resistance, dark noise, count rate capability, charge abstraction lifetime, and image characteristics of a number of standard 33 mm diameter microsphere plates (of thickness 0.7 and 1.4 mm), operated both singly and as two-stage multipliers. We also describe a simple Monte-Carlo model of MSP operation, which enables us to estimate numerically a number of MSP characteristics, including (1) output pulse height distributions (PHDs), (2) output electron spatial and energy distributions, and (3) transit time distributions.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report on the results of a synchrotron calibration of two identical microchannel plate (MCP) detectors carried out at the CCL Daresbury synchrotron radiation source (SRS). The SRS was run with low ring current to allow operation of the detectors in photon-counting mode. Both detectors were half coated with KBr and half with CsI. Detector 1 was calibrated, for both photocathodes, in 1 eV steps over the energy range 50 - 350 eV, on SRS beamline 6.1. We present measurements of edge-related absolute quantum efficiency features arising from both the photocathodes and the underlying lead silicate glass. We also describe the results of charge abstraction lifetests of Detector 1, made possible by the small cross section and relatively high peak count rate of the line 6.1 x-ray beam. A preliminary analysis of the calibration of detector 2 in 3 eV steps over the energy range 2000 - 6000 eV (on IRC beamline 4.2) is also presented.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The high resolution camera (HRC) will be one of the two focal plane instruments on the Advanced X-ray Astrophysics Facility (AXAF). AXAF is a major NASA space observatory and is scheduled for launch in 1998. The essential elements of the HRC instruments are chevron pairs of microchannel plates (MCPs). The HRC MCPs provide x ray conversion and electron multiplication while maintaining high spatial and temporal resolution. In addition, the HRC MCPs will be the largest format, the lowest internal background, and the highest resolution of any MCP-based x-ray imaging detector. This paper presents results obtained in testing and evaluating flight candidate MCPs with emphasis on their low internal background out-of-band (high energy) response and their spatial uniformity.

Focused x-ray images are reported for 21 X 21mm2 microchannel plate (MCP) optics having an eleven micron square-channel geometry. These are the smallest channel size square-pore MCPs yet evaluated. Because the limiting focal spot size in such optics is twice the channel width, their construction represents a significant advance towards focusing elements capable of very high intensification. The MCPs were fabricated with channel length- to-diameter ratios of 40 to 1 and 75 to 1; with an open area fraction of 85%. X-ray images were first obtained at 0.28keV and 1.74keV using a planar MCP geometry with a zero degree bias angle. These images indicate that subtle deviations from an ideal square channel geometry (i.e. vertex 'radiusing') can strongly influence the focal spot structure. Finally, one of the MCPs was spherically 'slumped' to a 1m radius and remeasured in x-rays, demonstrating for the first time the operation of a slumped square-channel MCP.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe our recent synchrotron measurements of microchannel plate (MCP) quantum detection efficiency made in pulse-counting mode in a 40-300 eV band containing the L shell absorption edges of silicon. The significance of this data for the calibration of the HRC-S transmission grating detector for the AXAF-I X-ray observatory is discussed.

In the present paper, we describe X-ray images obtained using planar, square pore MCPs in `point-to-point' focusing mode. Angular resolution of 5 arcminutes fwhm has now been measured for full-field illumination of a hydrogen-reduced Galileo MCP (29 mm active diameter; approximately 44,000 active channels). Secondly, we report some preliminary metrology of square-pore microchannel plates using atomic force, scanning electron and optical microscopies. Finally, we extend our study of spherically-slumped, round-pore Philips MCPs operated as X-ray `beam expanders'.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, we consider the use of lead glass microchannel plates (MCPs) as focusing elements for soft x rays. In particular, we discuss the possible realization of the wide field-of- view `Lobster Eye'' astronomical optics originally proposed by Angel using MCPs with confocal channels of square cross-section. Preliminary laboratory measurements are presented of the point-to-point focusing of both white light and soft x rays by a planar square-pore MCP with 85 (mu) channels. The practical realization of a Lobster Eye x-ray monitor for a possible small satellite mission is considered.

We present further data on the linear polarisation sensitivity of CsI X-ray/UV photocathodes. A radical physical origin- "non local" photoemission- is proposed for the X-ray vectorial effect. Predictions from a uniaxial photocathode model are compared with measurements of (i) relative pulse quantum yields, relative current quantum yields and electron number distributions for both s- (electric vector perpendicular to the plane of incidence) and p- ( parallel to the plane of incidence) polarised soft X-rays in the wavelength range 4.6-125A and (ii) relative current quanm yields from illumination by partially-polarised, broad-band UV radiation with a modal wavelength of 1550A. An origin seated in the polarimeter geometry is also proposed for the off-axis "phase shift" phenomenon reported in previous papers. The impact of these measurements on (i) an understanding of soft X-ray Interactions with materials and (ii) the design and sensitivity of the Spectrum X-Gamma Photoemission Polarimeter is discussed ; our future plans for the investigation of photocathode physics are finally outlined.

Observations of afteremission in microchannel plate (MCP) detectors illuminated by low-energy ions or soft X-ray are reported. Possible mechanisms of delayed pulse generation in lead glass microchannel plate multipliers are discussed with reference to observations with MCPs of different chemical compositions. The findings of the study are discussed in relation to the use of MPC detectors in space astronomy and other fields.