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New two-dimensional (2D) position sensitive solid state pixel detectors with dedicated multi-channel mixed-signal front-end readout integrated circuits (ICs) have been developed for x-ray and gamma ray imaging. These pixel detectors were designed to be versatile and accommodate many types of position-sensitive solid-state sensors. These 2D pixel detectors are designed to address the needs of a wide range of photon counting applications with high energy resolution imaging, high spatial resolution and for fast photon counting with simultaneous multiple energy binning capability. The first family of these pixel detectors is intended for spectroscopy applications with sensors such as Si, Ge, GaAs, HgI2, PbI2, Se, CdTe and CdZnTe in a variety of configurations to detect and image x-rays and gamma-rays of energies up to 1.3 MeV. The second family is developed for fast photon counting with simultaneous energy binning. They can be used with similar solid state sensors. The third family is for high spatial resolution imaging with resolution down to 50 times 50 micron.

Blocking layers are used to reduce leakage current in amorphous selenium detectors. The effect of the thickness of the blocking layer on the presampling modulation transfer function (MTF) and on dark current was experimentally determined in prototype single-line CCD-based amorphous selenium (a-Se) x-ray detectors. The sampling pitch of the detectors evaluated was 25 {mu}m and the blocking layer thicknesses varied from 1 to 51 {mu}m. The blocking layers resided on the signal collection electrodes which, in this configuration, were used to collect electrons. The combined thickness of the blocking layer and a-Se bulk in each detector was {approx}200 {mu}m. As expected, the dark current increased monotonically as the thickness of the blocking layer was decreased. It was found that if the blocking layer thickness was small compared to the sampling pitch, it caused a negligible reduction in MTF. However, the MTF was observed to decrease dramatically at spatial frequencies near the Nyquist frequency as the blocking layer thickness approached or exceeded the electrode sampling pitch. This observed reduction in MTF is shown to be consistent with predictions of an electrostatic model wherein the image charge from the a-Se is trapped at a characteristic depth within the blocking layer, generally nearmore » the interface between the blocking layer and the a-Se bulk.« less

Hybrid CdZnTe, CdTe, GaAs, selenium and PbI 2 pixel detector arrays with 50×50 μm 2 pixel sizes that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. These detectors have superior X-ray quantum efficiency compared to either emulsion-based film, phosphor-based detectors or other low-Z, solid-state detectors such as silicon. During this work, CdZnTe and CdTe pixel detectors gave the best results. The other detectors are at very early stages of development and need significant improvement. Among other detectors, selenium is showing the highest potential. The preliminary results show that single crystal CdZnTe detectors yield better results in Detective Quantum Efficiency (DQE) as well as in images obtained from phantoms, compared to the polycrystalline CdZnTe detectors. This is due to the non-uniformities in the polycrystaline CdZnTe that degrade the charge transport properties. In this paper, preliminary results from thin (0.15 to 0.2 mm) CdZnTe and CdTe detectors will be presented in terms of MTF, DQE and phantom images. Because of the charge-coupling limitation of the readout Application Specific Integrated Circuit (ASIC) that was originally designed for Si detectors, the detector is biased to collect holes from the input. This charge collection mode limits the CdZnTe detector performance. Their DQE measurements yield 25% and 65% for the polycrystal and single-crystal CdZnTe detectors, respectively. Polycrystal CdTe test detectors were also hybridized to the same type charge readout chip. Since CdTe has much longer hole-propagation lengths compared to CdZnTe, it shows better performance in the hole-collecting mode. However, it suffers from polarization. Excellent images were also obtained from the CdTe detectors. Future work to redesign the readout ASIC and thus improve the detector performance will be discussed. These detectors can also be used for other medical radiography with increased thickness and also for industrial imaging such as non-destructive evaluation and non-destructive inspection.

New, high spatial resolution CdZnTe (CZT) and silicon (Si) pixel detectors are developed for high angular and high energy resolution X-ray astronomy. These detectors are proposed for use in wide field-of-view, imaging All-sky X-ray, and Gamma-ray Astronomy Monitor (AXGAM) in a possible future space mission. The high stopping power of CZT detectors combined with low-noise front-end readout electronics ASIC (application specific integrated circuit) makes possible an order of magnitude improvement in spatial (angular) and energy resolution in X-ray detection. The AXGAM instrument will be built in the form of a fine coded mask placed over two-dimensional, high spatial resolution and low energy threshold silicon and CZT pixel detector arrays. The preliminary test results obtained from our first silicon and CZT pixel detectors are presented. These detectors may also be used with or without modification for medical and industrial imaging.

Hybrid pixel detector arrays that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. This technology also has wide application possibilities in other fields of radiology or in industrial imaging, nondestructive evaluation (NDE) and nondestructive inspection (NDI). These detectors have potentially superior properties compared to either emulsion-based film-screen systems which has nonlinear response to X-rays, or phosphor-based detectors in which there is an intermediate step of X-ray to light photon conversion (Feig and Yaffe, Radiol. Clinics North America 33 (1995) 1205–1230). Potential advantages of direct conversion detectors are high quantum efficiencies (QE) of 98% or higher (for 0.3 mm thick CdZnTe detector with 20 keV X-rays), improved contrast, high sensitivity and low intrinsic noise. These factors are expected to contribute to high detective quantum efficiency (DQE). The prototype hybrid pixel detector developed has 50×50 μm pixel size, and is designed to have linear response to X-rays, and can support a dynamic range up to 14 bits. Modulation Transfer Function (MTF) is measured on a 1-mm silicon detector system where 10% or better modulations are obtained at 10 lp/mm spatial frequency. Preliminary DQE measurements of the same detector yields a value of 75% at zero spatial frequency. In this paper, we report results obtained from our first full size prototype readout ASIC chips hybridized with both silicon and CdZnTe detector arrays and present preliminary MTF and DQE measurement results as well as some test images.

Hybrid pixel detector arrays that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. This technology also has wide application possibilities in other fields of radiology and in industrial imaging for applications in nondestructive evaluation and inspection. These detectors have potentially superior properties compared to either emulsion based film, which has nonlinear response to X-rays, or phosphor-based detectors in which there is an intermediate step of X-ray to light photon conversion. Potential advantages of direct conversion detectors are high quantum efficiencies (QE) of 98% or higher (for 0.3 mm thick CdZnTe detector with 20 keV X-rays), improved contrast, high sensitivity and low intrinsic noise. These factors are expected to contribute to high detective quantum efficiency (DQE). The prototype hybrid pixel detector developed has 50/spl times/50 microns pixel size, and is designed to have linear response to X-rays, and can support a dynamic range of 14 bits. Modulation Transfer Function (MTF) is measured on a l-mm silicon detector system where 10% or better modulations are obtained at 10 lp/mm spatial frequency. Preliminary DQE measurements of the same system yields a value of 55% at zero spatial frequency. Here, the authors report data of their first full size prototype readout ASIC chips hybridized with both silicon and CdZnTe detector arrays and present initial MTF and DQE measurement results as well as some test images.

A multichannel mixed signal Application Specific Integrated Circuit (ASIC) chip for front end readout electronics of position sensitive solid state detectors has been developed. It is called Readout Electronics for Nuclear Applications (RENA). This chip can be used for large number of channels and high-energy resolution astrophysics and nuclear physics detectors. It can also be applied for medical and industrial imaging of X-rays and gamma rays. The RENA chip is a monolithic integrated circuit and has 32 channels with low-noise high input impedance charge sensitive amplifiers. It works in pulse counting mode with good energy resolution. It also has a self-triggering output which is essential for nuclear applications when the incident radiation arrives at random. Different, externally selectable, operational modes that includes a sparse readout mode is available to increase data throughput. It also has externally selectable shaping (peaking) times. A full-scale prototype RENA chip version III is being manufactured. The results of tests done on the third prototype chip connected to a CdZnTe pad detector array will be presented.

A wide field-of-view, arcsecond imaging, high energy resolution X-ray and low energy gamma ray detector is proposed for a future space mission. It is specifically designed to detect and find counterparts at other wavelengths for /spl gamma/-ray bursts (GRBs). Detection of GRBs requires wide field-of-view (/spl pi/ to 2/spl pi/ field-of-view) and high sensitivity. This will be achieved by using high quantum efficiency CdZnTe pixel detectors with a low energy threshold (few keV) to observe the larger flux levels at lower energies, and large effective area (625 to 1000 cm) per coded aperture imaging module. Counterpart searches can only be done with ultra-high angular resolution detectors (10 to 30" FWHM) which gives 1 to 5" position determination especially for strong GRBs. A few arcsecond size error box is expected to contain at most one object observed at another wavelength. This will be achieved by using ultra-high spatial resolution pixel detectors (50/spl times/50 to 100/spl times/100 /spl mu/m) and a similar resolution coded aperture to achieve the required angular resolution. The low energy range may provide important new information on GRBs and the high energy resolution is expected to help in the observation and identification of emission and absorption lines in the GRB spectrum. The effective energy range is planned to be 2 to 200 keV which is exceptionally wide for such a detector. The major scientific goals of the proposed mission in addition to continuously monitoring GRBs, is to observe AGN, transient phenomena, isolated and binary pulsars, and solar flares. A space-deployed AXGAM detector is expected to observe a few hundred GRBs per year.

A high sensitivity electronically collimated gamma camera is under development at NOVA. The proposed detector has electronic collimation and will measure the direction of the incident /spl gamma/-ray directly, hence eliminating the need for a physical collimator. This is accomplished by using the Compton double scatter technique. A feasibility study was successfully completed and prototype fabrication started. The new detector is expected to have 3 to 10 times improvement over the present gamma cameras. The high sensitivity is expected to allow fast imaging on time scales of 1 to 2 min and may open the way for dynamic metabolism visualization and Multi Gated Acquisition (MUGA) studies. The prototype is designed to have a high spatial resolution which is 2 to 3 times better compared to present gamma cameras. It is expected to have improved energy resolution by a factor of 2 to 4. Good energy resolution will enable discrimination against and scattered /spl gamma/-ray background with higher effectiveness than presently available. This will improve the signal-to-noise ratio and improve image quality. The detector can be designed as a single gamma camera or formed into a cylindrical detector and used as a tomographic SPECT imager. A modified smaller version may be directly applied to scintimammography.

We have developed a new readout ASIC for high-resolution gamma-ray spectroscopy, which can be flip-chip bonded directly to a two-dimensional solid-state pixel array. This chip, called DANA-3 (Detector Array for Nuclear Applications), has a 16 × x16 array of anode readout channels with a pitch of 0.5 mm × 0.5 mm, plus an extra channel optimized for the cathode signals. To minimize power consumption, the ASIC was designed in a 0.18 µm process. To further reduce power dissipation, we incorporated automatic switching between different modes of operation (Watchdog, Counting, and Spectroscopy) depending on user-selectable radiation level thresholds, an ability to power down unused channels, and a low-power, low-noise differential I/O interface. Power dissipation ranges from 7 mW in watchdog mode to 50 mW with all channels enabled in spectroscopy mode. In the latter mode, the circuit features low-noise, high-energy resolution performance and allows for depth-of-interaction optimization using the cathode signal. The ASIC layout is three-side abuttable, so individual circuits can be combined into larger arrays. For optimal performance of the ASIC in different applications the main parameters of the analog channels can be programmed (globally or individually) over a wide range. In this paper we describe the ASIC design details and preliminary results of lab testing and characterization, including noise measurements and testing with pulser signals.

We have developed a prototype of a scalable high-resolution direction and energy sensitive gamma-ray detection system that operates in both coded aperture (CA) and Compton scatter (CS) modes to obtain optimal efficiency and angular resolution over a wide energy range. The design consists of an active coded aperture constructed from 52 individual CZT planar detectors each measuring 3×3×6 mm3 arranged in a MURA pattern on a 10×10 grid, with a monolithic 20×20×5 mm3 pixelated (8×8) CZT array serving as the focal plane. The combined mode is achieved by using the aperture plane array for both Compton scattering of high-energy photons and as a coded mask for low-energy radiation. The prototype instrument was built using two RENA-3 test systems, one each for the aperture and the focal plane, stacked on top of each other at a distance of 130 mm. The test systems were modified to coordinate (synchronize) readout and provide coincidence information of events within a user-adjustable 40-1,280 ns window. The measured angular resolution of the device is

The field of high energy gamma-ray astronomy grew tremendously in the last decade due to the launch of the EGRET detector on the Compton Gamma-Ray Observatory in 1991 and the proliferation of ground-based air Cherenkov telescopes (ACTs) such as the Whipple 10 meter reflector. Interestingly, the ground-based telescopes only see 4–5 of the over 170 objects detected by EGRET. A simple extrapolation of the EGRET objects' energy spectra up to the energies which the ACTs are sensitive suggests that many of them should have been detected. The key to resolving this lack of detections is to observe these sources in the previously unobserved 20–250 GeV energy range. The Solar Two Observatory collaboration is developing a secondary optics system on the central tower of the world's largest solar energy pilot plant, Solar Two, to observe gamma-ray sources in this energy range. The progress in building the secondary optics system to be used to image ∼64 heliostats at Solar Two located in Barstow, California, is presented. We hope to design and build this detector over the next 2 years.

We have developed a pixel detector hybrid called DANA-2 (Detector Array for Nuclear Applications). DANA-2 consists of a two-dimensional, monolithic Cadmium Zinc Telluride (CZT) detector array flip-chip bonded directly to a readout IC designed for high energy resolution. Both the detector and the IC have 16 × 16 pixels with a pitch of 0.5 mm × 0.5 mm; the detector thickness is 3 mm. Each readout channel features a low-noise, charge-sensitive input amplifier with continuous-reset feedback and two selectable energy ranges; a gain amplifier with a five-bit gain adjustment and eight-bit offset DAC; a shaper with eight selectable shaping times ranging from 0.5 μs to 4 μs; a peak detector; and a trigger comparator. The data readout is controlled by a programmable token logic, which affords the user a high degree of flexibility in the selection of nearest-neighbor channels to be read out to account for charge sharing between pixels. To process the signals from the detector cathode, one of the readout channels, which is normally connected to a corner pixel, can instead be connected to the cathode through a dedicated I/O pad. The different characteristics of these cathode signals are accommodated through user configuration options for the signal polarity and input FET size. Other features of DANA-2 include the ability to disable the trigger on any channel and thus turn off “hot” pixels, and several test features such as an AC-coupled test signal input and the option to operate any peak detector in follower mode and connect it to the analog output to continuously monitor the shaper signal. We present below details of the DANA-2 design and first results from its performance characterization.

The RENA-3 (Readout Electronics for Nuclear Applications) is a 36-channel self-resetting, charge sensitive amplifier/shaper IC with trigger output, wide energy range and sparse readout designed for use with position-sensitive, spectroscopy-grade radiation detectors. It has in recent years been favored to provide the front-end electronics in prototype instruments for various applications — from space physics research through medical imaging to homeland security — that employ CZT or CdTe in the form of planar sensor assemblies or monolithic pixel/strip arrays. We will present a summary of spectroscopic data drawn from the body of RENA-3-based results obtained in our laboratories and by other RENA-3 users. Spectroscopic performance metrics will be discussed relative to the requirements of the specific application targeted in each case as well as from the general standpoint of what may be achievable within this detector-array/RENA-3 approach. A method to automate the test and calibration of RENA-3 ICs will also be described.

We have developed a new, improved version of the XENA (X-ray ENergy-binning Applications) readout IC for solid-state x-ray detector arrays, which we call XENA-2. This IC consists of 32 readout channels, each with charge-sensitive input amplifier, two-stage gain amplifier, and five comparators followed by 16-bit pulse counters. The resistive feedback of the input amplifier is provided by a transconductance circuit with continuously variable, user-controlled transconductance, which allows the amplifier’s shaping time to be varied between 100 to 150 ns and 4 μs. Two input amplitude ranges, 7 fC and 30 fC nominal (200 keV and 800 keV, respectively, for Cadmium Zinc Telluride), can be selected by switching different capacitors into the feedback path. The gain amplifier design includes a five-bit gain adjustment and a ten-bit R-2R offset DAC. The five comparator threshold voltages are supplied externally and are common to all channels; digitally controlled threshold adjustments at each comparator allow to compensate for process variations. Readout of the counters, over a 16-bit data bus, takes approximately 20 μs. Two additional analog-only channels (that is, without the comparators and counters) are provided, one at each end of the channel array; they are used for test purposes and to improve the uniformity of the full channels. Compared to XENA, this new IC’s main improvement is significantly reduced noise, which allows for lower comparator thresholds and increased count rates. XENA-2 is fully pin-compatible with XENA and replaces it as the readout IC used in NOVA’s NEXIS detector system.

We have developed a new version of the MARY (MAmmogRaphY) pixel detector with its custom readout integrated circuit (IC) optimized for electron collection in semiconductor detectors such as CdZnTe (CZT), CdTe, a-Se and GaAs. This new pixel detector and readout IC, the MARY-N50, is essentially comprised of a 192 x 384 array of channels at a 50 μm x 50 μm pitch, which can be flip-chip bump-bonded with a matching detector pixel array. A 100 μm pitch pixel detector, the MARY-N100, was also developed, with a 64 x 192 pixel array. Standard features of both versions of MARY-N include: TDI (Time Delay Integration) or “staring” CCD readout capability; low noise and wide dynamic range; internal clock drivers; fat zero input; overflow control; multiple independent readout stages (24 for MARY-N50, 8 for MARY-N100) to accommodate large charge collection due to direct conversion.

We have developed high energy and high spatial resolution two-dimensional (2D) solid-state imaging pixel detectors and their custom integrated circuits (ICs). Solid-state pixel detectors and their readout ICs are now regarded to be an integral part of position-sensitive semiconductor detectors such as Si, CdTe and CdZnTe for x-ray and gamma-ray imaging. These detectors have a 2D structure. We have also developed one-dimensional (1D) detectors, which are mostly used for scanning type imaging. The new 2D pixel detectors we have developed can be used for both scanning and staring mode imaging applications. Because the requirements of various detector applications tend to be diverse, a custom IC is typically designed for a specific detector array. This often lengthens the time and raises the cost of system development. To help close the readout technology gap and facilitate advances in this field, we have been formulating and implementing strategies for instrumenting different detectors of a given application category with highly versatile ICs that meet a range of requirements. The solid-state pixel detectors that have been developed within this effort are presented below.

The RENA-3 (R Readout E eadout Electronics for N lectronics Nuclear A uclear Applications) is a multi-channel mixed-signal integrated circuit (IC) developed for the readout of position-sensitive solid-state detectors with excellent energy resolution. We will present results of experiments characterizing its performance as used with a variety of spectroscopy-grade detectors currently available in the industry, notably CZT pixel arrays as well as other detector configurations. The merits of specific RENA-3 design features vis-a-vis different detector applications will also be discussed.

We present the design and initial performance characterization of the XENA-2 readout IC for solid-state x-ray detector arrays. XENA-2 consists of 32 readout channels, each with charge-sensitive input amplifier, adjustable two-stage gain amplifier and five comparators with 16-bit pulse counters. Readout of the counters, over a 16-bit data bus, takes approximately 20 μs. Compared to the XENA chip, its predecessor, this new IC's main improvement is significantly reduced noise, which allows for lower comparator thresholds and increased count rates.

We have developed high energy and high spatial resolution 1D and 2D solid state imaging detectors and their custom integrated circuits (ICs). Readout ICs are now regarded to be an integral part of position-sensitive semiconductor detectors, especially for Si and CdZnTe for x-ray and gamma-ray imaging. These detectors have a 1D or 2D structure. The 1D structure types are mostly used for scanning purposes with some staring type imaging while 2D pixel detectors can be used for both scanning and staring mode imaging applications. Because the requirements of various detector applications tend to be diverse, a custom IC is typically designed for a specific detector array. This often lengthens the time and raises the cost of system development. To help close the readout technology gap and facilitate advances in this field, we have been formulating and implementing strategies for instrumenting different detectors of a given application category with highly versatile ICs that meet a range of requirements. The solid-state detectors and their ICs that have been developed within this effort are presented.

Multiple-site interactions initiated by Compton scattering are the primary interaction processes of gamma-rays in CZT in ~0.2 - several MeV range. Thus, exploiting gamma-rays as directional and spectral diagnostic probes requires detectors with 3-D resolution that resolve and measure individual interaction site's locations and energies. Desirable capabilities for Compton telescopes appear to be a spatial resolution of ~1 mm and an energy resolution of ~1 percent. Such capabilities are also important for coded mask imagers above 250 keV, where 3-D resolution can greatly improve the identification of a gamma-ray's initial interaction site, which is crucial for imaging. Significantly improved spectral resolution can be anticipated with CZT when multi-site interactions are resolved. This will allow each site's energy signals to be corrected for the site's specific signal loss characteristics, and the summed energies will then provide an accurate measure of the incident gamma-ray energy. We report on progress toward the development of 5 - 10 mm thick CZT detectors and electronics that are pursuing these objectives. Position sensing is provided by anode pixels with ~1 mm pitch for x-y positions and charge drift times for z-positions. Detectors are read out with the new RENA-2 ASIC. This chip contains preamplifiers, shaping amplifiers, threshold triggering, and peak detection for each of its 36 channels. To optimize energy resolution for various detector types and event rates, the RENA-2's peaking times and other parameters are adjustable. Each channel has a novel fast time stamp function that can record interaction times to ~10 nsec, allowing precise measurements of charge drift times and making PET imaging possible. The detector and ASIC designs are described and results are presented on tests of thresholding, energy resolution, and time resolution

We have developed a multi-channel, mixed-signal integrated circuit (IC) as part of a resource-conserving approach to the design of instruments for missions flown under the Geospace Missions Network (GMN) of NASA's Living With a Star (LWS) program. Specifically, the IC was designed to read out microchannel plates (MCPs) which allow detection of single hot plasma particle by emitting a pulse of charge when struck by the plasma particle. The IC, named AIDA (AlowbarmplIlowbarfier Dlowbariscriminator AlowbarSIC) includes several Charge-Amplifier Discrminators in one package without sacrificing performance, thus simplifying the MCP electronics and saving on space, power and cost. Reduction of power and mass requirements by several tens of percent relative to existing MCP instrument electronics was the primary goal. A secondary goal was to integrate the pulse counting function into the IC, thereby eliminating the need for additional counters and conserving resources further. We present the features and capabilities of the AIDA IC and evaluation system, and initial characterization data for the chip.

A multi-channel front-end readout IC is developed for position sensitive solid-state detectors. It is called RENA-3. It has 36 low noise channels. Each channel has externally selectable input polarity. The channel inputs are optimized for 2 or 9 pF detector capacitance, which is externally selectable. It also has selectable dual energy range, 56K and 338K electrons (250 keV and 1.5 Mev for CZT, respectively). A fast trigger output is provided applications that require timing. A novel circuit produces arrival time difference measurement for each channel. It is developed to serve as front-end readout electronics for a variety of position-sensitive solid-state semiconductor detectors such as CdZnTe, Si, GaAs and HgI2. It also has flexibility for use with other types of solid-state detectors such as Ge, Se, PbI2 and CdTe in a multichannel strip or pixel geometry to detect and image x-rays and gamma-rays with energies up to 1.3 MeV. Also a novel register circuit and process allows nearest neighbor readout capability for pixel detectors. Combination of RENA-3 chips with a variety of semiconductor detectors would be suitable for numerous applications in astrophysics, nuclear physics, nuclear medicine, security and industrial imaging. Some possible applications include gamma camera, SPECT, small animal PET and SPECT, nuclear source detection and spectroscopy, space x-ray and gamma-ray astronomy missions, NDE and NDI.

We have developed custom two-dimensional (2-D) mixed signal readout integrated circuits (ICs) for advanced position sensitive hybrid solid-state radiation detectors. The 2-D readout ICs are an integral part of hybrid semiconductor pixel detectors developed for x-ray, gamma-ray and charged particle imaging. Different detector applications require custom IC, which is typically designed for a specific 2-D detector array. Therefore, it is challenging to develop generic ICs to meet a range of applications in different complementing fields. To approach this aim NOVA has put significant effort on developing its ICs as flexible as possible to address differences in the fields of application. Therefore, these ICs embody versatile and adaptable functions as well as selectable features. An overview of 2-D ICs recently developed at NOVA and their functionality and features will be presented. Preliminary test results will be discussed. These ICs can be used for applications ranging from x-ray astronomy and medical imaging to munitions, security and industrial inspection. Some potential applications are: gamma camera; SPECT; PET; CT; digital mammography & radiography; baggage scanner; NDI and NDE.

In this paper we present the status and preliminary results from a CZT development program of fine pixel detectors. These are to be used at the focus of high-energy grazing-incidence optics (20-75 keV) of the HERO-Experiment under construction at the Marshall Space Flight Center.

A new mixed signal integrated circuit (IC) for front-end readout electronics of position sensitive solid state detectors has been developed. It is called RENA-2 and can be used for readout of position sensitive solid state detectors such as CdTe, CdZnTe, Ge, GaAs, HgI2, PbI2, Se and Si strip, pad and pixel detectors, with large numbers of channels. It is designed to have very low noise and, therefore, high energy resolution. It has numerous possible applications in astrophysics, medical and industrial imaging, security such as baggage inspection and nuclear physics. The RENA-2 chip is a monolithic integrated circuit and has 36 channels with low noise, high input impedance charge sensitive amplifiers. The RENA-2 chip can be optimized for individual applications

We have developed compact detector modules for high-resolution PET imaging. The modules consist of arrays of four by four 20 mm long LYSO crystals whose scintillation signals are read by avalanche photodiode arrays. The scintillator arrays are instrumented at both ends to facilitate depth-of-interaction determination by measuring the pulse-height ratio between the two ends of the LYSO crystal. To process the diode signals, we have developed a custom multi-channel integrated readout chip designed for excellent coincidence time resolution and low power dissipation. The IC offers various configuration options to allow for a high degree of flexibility in the design of the imaging system

A simple x-ray detector that utilizes amorphous selenium (a-Se) directly deposited on a specially-designed CCD (charge coupled device) with a 25 micrometer del (detector element) pitch is described. This simple detector has been used to test the feasibility of creating digital mammography detectors. To enable the use of electron transport CCDs with a-Se, we have developed a-Se hole blocking layers to permit the transfer of electrons to the CCD while suppressing hole leakage current in the presence of the high negative bias (~1000 V) required to make the a-Se x-ray sensitive. We report measurements of the charge transfer efficiency (CTE), dark signal, x-ray sensitivity, x-ray signal linearity, and x-ray MTF (modulation transfer function) of the simple detector. As the thickness of the a-Se hole blocking layer was increased, the MTF decreased. For a thin (1 micrometer) blocking layer the MTF at a spatial frequency of 20 cycles/mm was 0.4.

Large area, high spatial resolution CdZnTe pixel detectors are being developed for hard X-ray astronomy. We have designed and fabricated custom readout chips and bump-bond these to pixelated CdZnTe crystals using indium bump bonding technology. The resulting detectors have 16 x 16 pixels with 300 micron pitch, enabling low noise operation and permitting detailed imaging. These devices are ideally suited for the focal plane of future high-resolution hard x-ray focusing telescopes now being considered, such as the HXT on Constellation-X. An initial demonstration using the sparse read-out capabilities of these detectors is presented.

A new high-resolution detector has been developed for use in a slot-scanned digital mammography system. The detector is a hybrid device that consists of a CCD operating in time-delay integration mode that is bonded to a 150-μm-thick CdZnTephotoconductor array. The CCD was designed with a detector element pitch of 50 μm. Two devices were evaluated with differing crystalline quality. Incomplete charge collection was a source of reduction in DQE. This occurs in both devices due to characteristically low mobility-lifetime products for CdZnTe, with the greatest losses demonstrated by the multicrystalline sample. The mobility-lifetime products for the multicrystalline device were found to be 2.4×10 −4 and 4.0×10 −7 cm 2 /V for electrons and holes, respectively. The device constructed with higher quality single crystalCdZnTe demonstrated mobility-lifetime products of 1.0×10 −4 and 4.4×10 −6 cm 2 /V for electrons and holes. The MTF and DQE for the device were measured at several exposures and results were compared to predictions from a linear systems model of signal and noise propagation. The MTF at a spatial frequency of 10 mm −1 exceeded 0.18 and 0.56 along the scan and slot directions, respectively. Scanning motion and CCD design limited the resolution along the scan direction. For an x-ray beam from a tungsten target tube with 40 μm molybdenum filtration operated at 26 kV, the single crystaldevice demonstrated a DQE(0) of 0.70±0.02 at 7.1×10 −6 C/kg (27 mR) exposure to the detector, despite its relatively poor charge collection efficiency.

Industrial X‐ray radiography is often done using a broad band energy source and always a broad band energy detector. There exist several major advantages in the use of narrow band sources and or detectors, one of which is the separation of scattered radiation from primary radiation. ARDEC has developed a large detector array system in which every detector element acts like a multi‐channel analyzer. A radiographic image is created from the number of photons detected in each detector element, rather than from the total energy absorbed in the elements. For high energies, 25 KeV to 4 MeV, used in radiography, energy discriminating detectors have been limited to less than 20,000 photons per second per detector element. This rate is much too slow for practical radiography. Our detector system processes over two million events per second per detector pixel, making radiographic imaging practical. This paper expounds on the advantages of the ARDEC radiographic imaging process.

A wide field-of-view, arcsecond imaging, high energy resolution X-ray and low energy gamma ray detector is proposed for a future space mission. It is specifically designed to detect and find counterparts at other wavelengths for gamma ray bursts (GRBs). Detection of GRBs require wide field-of-view (/spl pi/ to 2/spl pi/ field-of-view) and high sensitivity. This will be achieved by using high quantum efficiency CdZnTe pixel detectors, low energy threshold (few keV) to observe larger flux levels that may be possible at lower energies and large effective area (625 to 1,000 cm/sup 2/) per coded aperture imaging module. Counterpart searches can only be done with ultra high angular resolution (10 to 30 arcsecond FWHM) which gives 1 to 5 arcsecond position determination especially for strong GRBs. A few arcsecond resolution error box is expected to contain only one counterpart observed at another wavelength. This will be achieved by using ultra high spatial resolution pixel detectors (50/spl times/50 to 100/spl times/100 micron) and a similar resolution coded aperture to achieve the required angular resolution. AXGAM also has two other important advantages over similar detectors: (1) excellent low energy response (>1 keV) and (2) high energy resolution (

A mixed signal Application Specific Integrated Circuit (ASIC) chip for front end readout electronics of position sensitive solid state detectors has been developed. The new ASIC is called RENA (Readout Electronics for Nuclear Applications). This chip can be used for large number of channels and high energy resolution astrophysics and nuclear physics detectors, and medical imaging instruments such as solid state gamma camera, Compton SPECT and Intraoperative probes. It can also be used for industrial imaging of X-rays and gamma rays used in nondestructive evaluation (NDE) and inspection (NDI). The RENA chip is a monolithic integrated circuit and has 32 channels with low noise charge sensitive amplifiers followed by a polarity amplifier and a high quality shaper circuit. It works in pulse counting mode with good energy resolution. It also has a self-triggering output which is essential for nuclear applications when the incident radiation arrives at random. Different, externally selectable, operational modes that include a sparse readout mode are available to increase data throughput. It also has externally selectable shaping (peaking) times. A full scale prototype RENA chip has been manufactured. The preliminary results of tests done on the prototype chip are presented.

A Readout Electronics for Nuclear Applications (RENA) Chip has been developed to read out position sensitive solid state detectors for the nuclear instruments. This chip can also be used for medical and industrial imaging of X-rays and gamma rays. It is a multi channel monolithic mixed signal application specific integrated circuit (ASIC) chip. The RENA chip has 32 channels with low noise charge sensitive amplifier inputs. It works in pulse counting mode with good energy resolution. It also has a self triggering output which is essential for nuclear applications when the incident radiation arrive at random. Different, externally selectable, operational modes that includes a sparse readout mode is available to increase data throughput. The design of the chip and the results of tests done on a full scale prototype chip will be presented.

An ASIC-based readout electronics scheme is under development for high resolution, compact PET imagers based on independent readout of all channels of LSO scintillator and avalanche photodiode (APD) arrays. Depth of interaction is obtained by readout of both ends of the LSO crystals. A low power, highly integrated design is critical. We report here on a discrete electronics prototype, running at 22 mW per channel for the preamplifier and discriminator. The measured timing resolution is 3.6 ns FWHM, 9.2 ns full width at one tenth maximum, relative to an LSO/PMT detector, energy resolution is 13.3% FWHM at 511 keV, and depth of interaction position resolution is 2.5 mm FWHM throughout the full length of the crystal. Work is in progress towards an ASIC and a full scale prototype detector module suitable for a high resolution compact PET instrument.

New, high spatial resolution CdZnTe (CZT) and silicon (Si) pixel detectors are developed for high angular and high energy resolution X-ray astronomy. These detectors can be used for wide field-of-view all-sky X-ray, and gamma-ray monitors such as the AXGAM instrument and focusing X-ray imagers such as the high energy detector (HXT) proposed for the CONSTELLATION mission. The high stopping power of CZT detectors combined with low-noise front-end readout electronics ASIC (application specific integrated circuit) makes possible an order of magnitude improvement in spatial (angular) and energy resolution in X-ray detection. If silicon pixel detectors are used the energy threshold can be lowered. The preliminary test results obtained from our first silicon and CZT pixel detectors are presented. These detectors may also be used with or without modification for medical and industrial imaging.

A linear CdZnTe pad detector array with approximately 1 mm/sup 2/ pad area has been developed. The detector has a wide energy range from about 20 to 200 keV. A fast, low-noise monolithic mixed signal ASIC chip has been developed to read out these detector arrays. A prototype X-ray imaging system consisting of the CdZnTe detector array and the monolithic ASIC chip has been fabricated and tested. In this system, the detectors are abutted against each other to form an approximately 1 m long linear array. The system has been used to take preliminary scanned images of complex objects at various energies. New results obtained from this system is discussed.

The Keck Solar Two Gamma-Ray Observatory is a ground-based instrument is being developed to detect 20-300 GeV gamma rays by sampling the Cherenkov light generated as gamma rays and cosmic rays interact with the atmosphere. The observatory utilizes the Solar Two Pilot Power Plant in Barstow, California (Figure 1) which has the largest heliostat mirror area in the world. It has over 1,818 heliostats each with about 41 m2 mirror area. The total active area is over 75,000 m2. Thus, Keck Solar Two Gamma Ray Observatory has the potential to be the most sensitive ground-based gamma-ray detector between 20-300 GeV. The secondary mirror systems, each capable of viewing 32 heliostats has been designed. The secondary mirror systems also include the photomultiplier tube (PMT) camera, electronics, and heliostat field. The first secondary camera has been manufactured and it is being calibrated. Work on building the second secondary camera system with 32 heliostats has been started. When the second system is completed a 64 heliostat telescope will be ready to observe 50-300 GeV gamma rays. Further enlargement of the telescope to 128 or 256 heliostat is expected to lower the energy threshold to about 20 GeV.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Our collaboration is characterizing a prototype detector module designed for high energy X-ray astrophysics research covering the 20 - 250 keV energy range. The module consists of a three dimensional position sensitive CdZnTe detector, 25 mm X 25 mm X 2 mm, with 1 mm pitch crossed strip electrodes, an interleaved steering electrode, and an Application Specific Integrated Circuit (ASIC) for individual electrode readout. The newly developed readout system is compact, lightweight, has low power consumption and will lead to reduced system electronic noise. The detector is surrounded by a plastic anti-coincidence system for charged particles, and passive shielding that has been optimized based on results from two previous balloon flights. The first balloon flight test of the new detector module is scheduled for Fall 2000. In addition to our continuing balloon studies, we are investigating proton radiation damage effects and present preliminary results. After proton irradiation, the energy resolution is not significantly degraded, calibration photopeaks are down shifted by less than 10% in energy, and the depth of interaction dependence is nearly eliminated.

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A linear CdZnTe pad detector array with approximately 1 mm2 pad area has been developed. The detector has a wide energy range from about 20 to 200 keV. To read out these detector arrays, a fast, low-noise monolithic mixed signal ASIC chip has been developed. A prototype x-ray imaging system consisting of the CdZnTe detector array and the monolithic ASIC chip has been fabricated and tested. In this system, the detectors are abutted against each other to form an approximately 1 m long linear array. The system has been used to take preliminary scanned images of complex objects at various energies. New results from this system will be presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Digital mammography has demanding imaging requirements, including very high spatial resolution (50 micrometer) and SNR. To make efficient use of the radiation dose, it is also desirable that the DQE of the image receptor is high. To achieve these requirements, a prototype CCD read-out has been designed, which is hybridized to a semiconductor array to form a direct conversion detector that can be employed in a slot- scanned digital x-ray imaging system. The image quality of the detectors in which the CCD is hybridized to either a silicon photodiode array or a CdZnTe photoconductor array has been measured. A 1 mm thick silicon device has shown a DQE(f) of 0.64 at 0 mm -1 , falling to 0.14 at 10 mm -1 in the slot direction (20 keV). The CdZnTe hybrid device is very thin (150 micrometer) and has a theoretical DQE in excess of 0.9 at 20 keV. The resolution of the CdZnTe device is excellent, with an experimental MTF that is limited only by the detector element size, and the TDI scanning technique. However, the experimental DQE is lower than predicted, believed to be due to crystal non-uniformity, and excessive carrier trapping. Future work will investigate the improvement in image quality obtainable by using a very high purity single-crystal CdZnTe device.

The Solar Two Gamma-Ray Observatory is designed to close the energy gap between 20–300 GeV that is inaccessible by current instruments, such as the satellite-borne EGRET detector and the ground-based air Cherenkov telescopes. Utilizing the facilities of the Solar Two Power Plant in Barstow, CA, the observatory will detect the Cherenkov light generated as high-energy gamma rays and charged cosmic-ray particles interact with the atmosphere. With over 2000 heliostats available, Solar Two has the largest heliostat mirror area in the world and, thus, the potential to be the most sensitive gamma-ray detector at these energies. Construction of a secondary mirror system capable of imaging 32 heliostats is nearing completion with plans for the first observations of the Crab Nebula in late November. We report on the design, status and testing of this secondary mirror system including the optics, electronics, and heliostat field.

The Solar Two Gamma-Ray Observatory is a ground-based instrument designed to detect 20-300 GeV gamma rays by sampling the Cherenkov light generated as gamma rays and cosmic rays interact with the atmosphere. The observatory utilizes the solar two pilot power plant in Barstow, California which has the largest heliostat mirror area in the world. It has over 2,000 heliostats each with about 41 m 2 mirror are. the total active are is over 75,000 m 2 . Thus, Solar Two Observatory has the potential to be the most sensitive ground-based gamma-ray detector between 20-300 GeV. The secondary mirror system, each capable of viewing 32 heliostats has been designed. The secondary mirror systems also include the photomultiplier tube camera, electronics, and heliostat field. The first secondary camera system is now being manufactured and tested.

The FiberGLAST scintillating fiber telescope is a large-area instrument concept for NASA's GLAST program. The detector is designed for high-energy gamma-ray astronomy, and uses plastic scintillating fibers to combine a photon pair tracking telescope and a calorimeter into a single instrument. A small prototype detector has been tested with high energy photons at the Thomas Jefferson National Accelerator Facility. We report on the result of this beam test, including scintillating fiber performance, photon track reconstruction, angular resolution, and detector efficiency.

The FARXITE balloon payload concept contains 10 co-aligned, hard X-ray telescopes, each containing a set ofnested multilayer mirror modules and an actively shielded CZT strip detector at each focal plane. The 500 micronstrip pitch provides 26 arcsecond pixels at the 4m focal length of FARJ(ITE. The active shielding and advancedCZT detector techniques reduce the background at float altitudes to a few times iO counts/cm2 s keY. We describethese advanced detectors and how they allow us to meet the scientific objectives of the FAR3UTE program.Keywords: X-ray astronomy, CZT detectors, telescopes, balloons 1. INTRODUCTION The Fine Angular Resolution X-ray Imaging TelescopE (FARJ(ITE, pronounced "far sight") combines state-of-the-art hard X-ray mirrors and room temperature semiconductor (CZT) detectors, which are designed to fly on along duration balloon gondola with an advanced pointing system. One scientific goal of the FARXITE mission isimaging with sub-arcminute resolution deeper than ever before with iO ergs/s sensitivity in the 20-90 keV rangeat the Galactic center. This goal requires both spatial and spectral resolution at hard X-ray energies. FAR.XITE ischaracterized by

New, high spatial resolution CdZnTe (CZT) and silicon (Si) pixel detectors are highly suitable for x-ray astronomy. These detectors are planned for use in wide field of view, imaging x-ray, and low energy gamma-ray all-sky monitor (AXGAM) in a future space mission. The high stopping power of CZT detectors combined with low-noise front-end readout makes possible an order of magnitude improvement in spatial and energy resolution in x-ray detection. The AXGAM instrument will be built in the form of a fine coded aperture placed over two-dimensional, high spatial resolution and low energy threshold CZT pixel detector array. The preliminary result of CZT and silicon pixel detector test with low-noise readout electronics system are presented. These detectors may also be used with or without modification for medical and industrial imaging.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A scintillating fiber detector is currently being studied for the NASA Gamma-Ray Large Area Space Telescope (GLAST) mission. This detector utilizes modules composed of a thin converter sheet followed by an x, y plane of scintillating fibers to examine the shower of particles created by high energy gamma-rays interacting in the converter material. The detector is composed of a tracker with 90 such modular planes and a calorimeter with 36 planes. The two major component of this detector are the scintillating fibers and their associated photodetectors. Here we present current status of development and test result of both of these. The Hamamatsu R5900-00-M64 multianode photomultiplier tube (MAPMT) is the baseline readout device. A characterization of this device has been performed including noise, cross- talk, gain variation, vibration, and thermal/vacuum test. A prototype fiber/MAPMT system has been tested at the Center for Advanced Microstructures and Devices at Louisiana State University with a photon beam and preliminary results are presented.

A digital mammography system in which the x-ray sensitive device is a solid-state direct conversion detector is under development. This detector is a 1 mm thick silicon photodiode array hybridized to a CCD read-out, with a 50 micrometer pixel pitch. The detector is designed to be used in a slot-scanned system using time-delay integration (TDI) for signal acquisition. To handle the large signal generated in the photodiode, a novel read-out technique was used, in which charge was integrated 'on-chip' over a small number of rows, and the output of each of these sections was digitally summed 'off-chip' to produce the total integrated signal for each pixel in the image. This two-stage integration process not only allows easy acquisition of large signals, it effectively increases bit depth from 12 bits (for a single section) to approximately 16 (for the total integrated signal). The image quality of the device has been measured and compared to predictions based on cascaded linear systems theory. The resolution of the new detector was determined from the modulation transfer function (MTF) which was obtained from over-sampled edge spread functions (ESF). The ESF was measured in both the scan and slot directions from four repeated images of a tantalum edge. Noise power spectra (NPS) were determined from 40 repeated flat-field images at each of several x-ray exposures. By combining the MTF and NPS measurements, the detective quantum efficiency (DQE) was also determined. The MTF in the non-scanned direction was found to greater than 20% at 10 mm-1 and slightly lower in the scanned direction (approximately equals 10% at 10 mm-1). In all cases, the DQE was at least comparable to film-screen mammography receptors. The DQE at 120 mR detector exposure at zero spatial frequency ranged from 0.4 to 0.6 depending on the sample tested. Electronic noise was fairly low, contributing to less than plus or minus 7 ADU (out of a possible 98304 ADU). Future work will involve re-designing the prototype to use a photoconductor with higher density and atomic number to improve quantum interaction efficiency and reduce geometric constraints on image quality.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Recently the need for a higher level of integration in x-ray and gamma ray sensor systems has lead to several approaches of integrating read out electronics in a monolithic integrated circuit (IC). Typically these ICs are limited in their application to a specific problem. The Readout Electronics for Nuclear Applications (RENA) Integrated Circuit, presented here, is targeted for use in many energy sensor applications. The RENA IC has 32 parallel signal channels with, signal polarity control for use with either electron or hole collection from detectors. The input amplifier is optimized for a detector capacitance of 6 pF, but may be used with detector capacitances up to 50 pF. The Shapers' peaking time is digitally selectable, for optimum noise filtering, with peaking times geometrically spaced from 400 ns to 6 microsecond(s) . Up to 16 RENA ASICs may be daisy chained together to make a system with 512 detector channels. Various trigger modes are available with a user- defined threshold over the full signal range of 50K electronics. The circuits in the RENA are designed to be stable with no 'tweaking' control,s which allows an easy user interfaces.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.