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Results for “coded aperture imaging”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
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NASA NTRS1997

Hard X-ray imaging survey of the Galactic plane with the Caltech gamma-ray imaging payload GRIP-2

In a two-day balloon flight during October 1995, the Caltech coded aperture gamma ray imaging payload (GRIP-2) imaged various fields in the Galactic plane and center in the 25 to 600 keV energy band. The large phoswich detector, the 15 deg field of view, the 30 arcmin angular resolution and 6 arcmin point source localization capability of GRIP-2 provides the possibility of surveying the accreting binary population of the Galaxy at high energy. The instrument is described and preliminary imaging results are reported on. The capabilities of this instrument for hard X-ray/gamma ray imaging are demonstrated.

Corbel, S.↗
NASA NTRS1986

Voyager at Uranus

The engineering changes that had to be made in the Voyager 2 spacecraft in order to enable it to fly beyond the originally planned encounters with Jupiter and Saturn and the underlying engineering strategy leading to the encounter with Uranus are discussed. Fixes of the azimuth actuator failure, receiver failure, and memory failure, and capability upgrades of Image Data Compression, aperture augmentation protective coding, smear reduction, Image Motion Compensation, power management, and contingency planning are summarized. The use of the Computer Command Subsystem in the extension of the voyage is described. The ways in which the strategic priorities, including spacecraft preservation, protection of the near-encounter load, development of new ground and spacecraft capabilities, and repair or circumvention of existing spacecraft faults, were accomplished are reviewed, and the accomplishment of additional tasks is also discussed.

Mclaughlin, W. I.↗
NASA NTRS2011

Development of Tiled Imaging CZT Detectors for Sensitive Wide-Field Hard X-Ray Surveys to EXIST

Motivated by the proposed EXIST mission, a "medium-class" space observatory to survey black holes and the Early Universe proposed to the 2010 NAS/NRC Astronomy and Astrophysics Decadal Survey, we have developed the first "large" area 256 sq cm close-tiled (0.6 mm gaps) hard X-ray (20-600 keV) imaging detector employing pixelated (2.5 mm) CdZnTe (CZT) detectors, each 2 x 2 x 0.5 cubic cm. We summarize the design, development and operation of this detector array (8 x 8 CZTs) and its performance as the imager for a coded aperture telescope on a high altitude (40 km) balloon flight in October. 2009, as the ProtoEX1STl payload. We then outline our current development of a second-generation imager, ProtcEXIST2. with 0.6 mm pixels on a 32 x 32 array on each CZT, and how it will lead to the ultimate imaging system needed for EXIST. Other applications of this technology will also be mentioned.

Grindlay, J.↗
NASA NTRS1993

Gamma-ray imaging with germanium detectors

Externally segmented germanium detectors promise a breakthrough in gamma-ray imaging capabilities while retaining the superb energy resolution of germanium spectrometers. By combining existing position-sensitive detectors with an appropriate code aperture, two-dimensional imaging with 0.2-deg angular resolution becomes practical for a typical balloon experiment. Much finer resolutions are possible with larger separations between detectors and the coded aperture as would be applicable for space-based or lunar-based observatories. Two coaxial germanium detectors divided into five external segments have been fabricated and have undergone extensive performance evaluation and imaging testing in our laboratory. These tests together with detailed Monte Carlo modeling calculations have demonstrated the great promise of this sensor technology for future gamma-ray missions.

Mahoney, W. A.↗
NASA NTRS1983

An imaging telescope for high energy gamma-ray astronomy

Recent tests of a gamma-ray imaging telescope, which incorporated a coded aperture mask and multiwire proportional counter system produced good images of a tritium target source which was used to generate the 20 MeV protons at a proton Van de Graaff accelerator. This paper indicates what performance might be expected if a large area drift chamber were used in conjunction with a coded aperture mask. The prospects for achieving significant scientific results if such a system were flown on a variety of space vehicles are discussed.

Frye, G.↗
NASA NTRS1988

A broad band X-ray imaging spectrophotometer for astrophysical studies

A broadband X-ray imaging spectrophotometer (BBXRIS) has been built for astrophysical studies. The BBXRIS is based on a large-imaging gas scintillation proportional counter (LIGSPC), a combination of a gas scintillation proportional counter and a multiwire proportional counter, which achieves 8 percent (FWHM) energy resolution and 1.5-mm (FWHM) spatial resolution at 5.9 keV. The LIGSPC can be integrated with a grazing incidence mirror and a coded aperture mask to provide imaging over a broad range of X-ray energies. The results of tests involving the LIGSPC and a coded aperture mask are presented, and possible applications of the BBXRIS are discussed.

Lum, Kenneth S. K.↗
NASA NTRS1987

Use of maximum entropy method with parallel processing machine

The maximum entropy method (MEM) and balanced correlation method were used to reconstruct the images of low-intensity X-ray objects obtained experimentally by means of a uniformly redundant array coded aperture system. The reconstructed images from MEM are clearly superior. However, the MEM algorithm is computationally more time-consuming because of its iterative nature. On the other hand, both the inherently two-dimensional character of images and the iterative computations of MEM suggest the use of parallel processing machines. Accordingly, computations were carried out on the massively parallel processor at Goddard Space Flight Center as well as on the serial processing machine VAX 8600, and the results are compared.

Yin, Lo I.↗
NASA NTRSDate not supplied

New Mission Concept: Compton Telescope with Coded Aperture Mask (GECCO) for MeV Gamma-ray Astronomy

The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel Explorer-class concept for a next-generation telescope covering the poorly explored hard X-ray and soft gamma-ray energy regimes. The instrument is based on a novel CdZnTe imaging calorimeter and a deployable coded aperture mask, which enable it to reach 1 arcmin angular resolution and 1% energy resolution. GECCO will connect the arcminute angular resolution observations from X-ray telescopes to high-energy images of the Galactic plane provided by Fermi-LAT, and will focus on the exploration of heavily populated sky regions such as the Galactic Center and the Carina and Cygnus regions to decipher the nature of their emission. These measurements will probe with unprecedented capabilities the possible origin of this emission as dark matter, new types of sources, or currently unresolved populations of point sources. Uncoded observations with GECCO’s Compton telescope will provide wide field-of-view sky monitoring for transient events, synergizing with gravitational wave and high-energy neutrino facilities. In addition, GECCO will conduct a high-sensitivity search for the positron sources in the Galactic Center responsible for the enigmatic 511 keV positron annihilation line excess, will search for as-yet untested candidates for dark matter, will detect and identify high-redshift blazars with excellent angular resolution, and will explore Galactic chemical evolution and sites of explosive element synthesis.

Alexander A Moiseev↗
NASA NTRS1983

A directional gamma-ray telescope using coded aperture techniques

A directional detector for gamma-ray astronomy has been developed to image sources in the energy range 0.1 to 5 MeV. An array of 35 gain stabilized bismuth germanate detectors, together with a coded aperture mask based on a uniformly redundant array allows imaging in 4 deg square sky bins over a 16 x 24 deg field-of-view. The position of a strong point source, such as the Crab Nebula, can be determined to within not more than about 1 deg. A complementary 'anti-mask' greatly reduces systematic effects arising from nonuniform background rates amongst the detectors. The telescope has an effective area of 190 sq cm and an energy resolution of 19.5 percent FWHM at 662 keV. Results of laboratory tests of the imaging system, including the ability to image multiple sources, uniformity of response over the field-of-view, and the effect of the 'anti-mask', are in good agreement with computer simulations. Features of the flight detector system are described and results of laboratory tests and computer simulations are reviewed. A balloon flight of the telescope is planned for the fall of 1982.

Mcconnell, M. L.↗
NASA NTRS2011

Technology Needs for Gamma Ray Astronomy

Gamma ray astronomy is currently in an exciting period of multiple missions and a wealth of data. Results from INTEGRAL, Fermi, AGILE, Suzaku and Swift are making large contributions to our knowledge of high energy processes in the universe. The advances are due to new detector and imaging technologies. The steps to date have been from scintillators to solid state detectors for sensors and from light buckets to coded aperture masks and pair telescopes for imagers. A key direction for the future is toward focusing telescopes pushing into the hard X-ray regime and Compton telescopes and pair telescopes with fine spatial resolution for medium and high energy gamma rays. These technologies will provide finer imaging of gamma-ray sources. Importantly, they will also enable large steps forward in sensitivity by reducing background.

Gehrels, Neil↗
NASA NTRS1985

A balloon-borne imaging gamma-ray telescope

A balloon-borne coded-aperture gamma-ray telescope for galactic and extragalactic astronomy observations is described. The instrument, called Gamma Ray Imaging Payload (GRIP), is designed for measurements in the energy range from 30 keV to 5 MeV with an angular resolution of 0.6 deg over a 20 deg field of view. Distinguishing characteristics of the telescope are a rotating hexagonal coded-aperture mask and a thick NaI scintillation camera. Rotating hexagonal coded-apertures and the development of thick scintillation cameras are discussed.

Althouse, W. E.↗
NASA NTRS1985

A balloon-borne imaging gamma-ray telescope

A balloon-borne coded-aperture gamma-ray telescope for galactic and extragalactic astronomy observations is described. The instrument, called GRIP (Gamma Ray Imaging Payload), is designed for measurements in the energy range from 30 keV to 5 MeV with an angular resolution of 0.6 deg over a 20 deg field of view. Distinguishing characteristics of the telescope are a rotating hexagonal coded-aperture mask and a thick NaI scintillation camera. Rotating hexagonal coded-apertures and the development of thick scintillation cameras are discussed.

Althouse, W. E.↗
NASA NTRS1984

Gamma-ray imaging with a rotating hexagonal uniformly redundant array

Laboratory experiments have been performed to demonstrate the capabilities of a gamma-ray imaging system employing a NaI Anger camera and a rotating coded aperture mask. The mask incorporates in its design a new type of hexagonal uniformly redundant array (HURA) which is essentially antisymmetric under 60 deg rotation. The image formation techniques are described and results are presented that demonstrate the imaging capability of the system for individual and multiple point sources of gamma-ray emission. The results are compared to analytical predictions for the imaging and point source localization capabilities of coded aperture systems using continuous detectors.

Cook, W. R.↗
NASA NTRS1992

Aperture codes for sensors viewing extended objects from space

The paper describes aperture codes viewing extended objects form space which find application in imaging an extended object which may have relatively low contrast, and whose lateral limits extend beyond the FOV of the sensor. Those elements of an extended object lying near the FOV limits are only partially coded, i.e., flux from those elements cannot cast a shadow of the entire aperture code onto the detector, as can elements near the center of the FOV. This has consequences for the algorithms used to reconstruct the image. The object field is divided into a number of elements which is smaller than the number of detector pixels, and a least squares fit to the data is performed. The methods used for choosing the matrices representing the aperture codes are discussed, and computer simulations of the effects of noise are described.

Curtis, C. C.↗
NASA NTRS2008

Hard-X-Ray/Soft-Gamma-Ray Imaging Sensor Assembly for Astronomy

An improved sensor assembly has been developed for astronomical imaging at photon energies ranging from 1 to 100 keV. The assembly includes a thallium-doped cesium iodide scintillator divided into pixels and coupled to an array of high-gain avalanche photodiodes (APDs). Optionally, the array of APDs can be operated without the scintillator to detect photons at energies below 15 keV. The array of APDs is connected to compact electronic readout circuitry that includes, among other things, 64 independent channels for detection of photons in various energy ranges, up to a maximum energy of 100 keV, at a count rate up to 3 kHz. The readout signals are digitized and processed by imaging software that performs "on-the-fly" analysis. The sensor assembly has been integrated into an imaging spectrometer, along with a pair of coded apertures (Fresnel zone plates) that are used in conjunction with the pixel layout to implement a shadow-masking technique to obtain relatively high spatial resolution without having to use extremely small pixels. Angular resolutions of about 20 arc-seconds have been measured. Thus, for example, the imaging spectrometer can be used to (1) determine both the energy spectrum of a distant x-ray source and the angular deviation of the source from the nominal line of sight of an x-ray telescope in which the spectrometer is mounted or (2) study the spatial and temporal development of solar flares, repeating - ray bursters, and other phenomena that emit transient radiation in the hard-x-ray/soft- -ray region of the electromagnetic spectrum.

Myers, Richard A.↗
NASA NTRS1995

The LXeCAT instrument for gamma-ray astrophysics

The Liquid Xenon Coded Aperture Telescope (LXeCAT) and its capability to image astrophysical gamma-ray sources in the MeV region is described. The gamma-ray detector is a Liquid Xenon Time Projection Chamber (LXeTPC) triggered by the primary scintillation light. Effective background rejection is a direct consequence of the intrinsic three-dimensional imaging capability of the LXeTPC. Initial results with a 10 liter prototype confirm an energy resolution of 6% FWHM, a position resolution of 1 mm RMS and a light triggering efficiency higher than 90% for 1 MeV gamma-rays.

Aprile, E.↗
NASA NTRS1988

High-spatial resolution and high-spectral resolution detector for use in the measurement of solar flare hard X-rays

In the areas of high spatial resolution, the evaluation of a hard X-ray detector with 65 micron spatial resolution for operation in the energy range from 30 to 400 keV is proposed. The basic detector is a thick large-area scintillator faceplate, composed of a matrix of high-density scintillating glass fibers, attached to a proximity type image intensifier tube with a resistive-anode digital readout system. Such a detector, combined with a coded-aperture mask, would be ideal for use as a modest-sized hard X-ray imaging instrument up to X-ray energies as high as several hundred keV. As an integral part of this study it was also proposed that several techniques be critically evaluated for X-ray image coding which could be used with this detector. In the area of high spectral resolution, it is proposed to evaluate two different types of detectors for use as X-ray spectrometers for solar flares: planar silicon detectors and high-purity germanium detectors (HPGe). Instruments utilizing these high-spatial-resolution detectors for hard X-ray imaging measurements from 30 to 400 keV and high-spectral-resolution detectors for measurements over a similar energy range would be ideally suited for making crucial solar flare observations during the upcoming maximum in the solar cycle.

Desai, U. D.↗
NASA NTRS1981

Temporal Aperture Modulation

The two types of modulation techniques useful to X-ray imaging are reviewed. The use of optimum coded temporal aperature modulation is shown, in certain cases, to offer an advantage over a spatial aperture modulator. Example applications of a diffuse anisotropic X-ray background experiment and a wide field of view hard X-ray imager are discussed.

Proctor, R. J.↗