Image reconstruction with a LaBr3-based rotational modulator

Budden, Brent; Case, G.; Cherry, M. L.

doi:10.1016/j.nima.2010.09.152

Cited by 9 publications

(7 citation statements)

References 17 publications

(15 reference statements)

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“…Calibrations of the newly-built data acquisition system are still ongoing. Based on earlier simulations and results with a previous version of the data acquisition system [18], we expect to be able to separate sources at 15 -20 ′ . Further improvement is expected by dithering the telescope around the source position.…”

Section: Discussionmentioning

confidence: 97%

Angular resolution obtained with a LaBr 3 -based rotational modulator

2009

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A Rotational Modulator (RM) gamma ray imager, consisting of a single grid of lead slats rotating above an array of detectors with diameter equal to the slat spacing, has the capability of providing angular resolution significantly better than the geometric resolution (i.e., the ratio of detector diameter to mask/detector separation). The sensitivity, weight, and angular resolution are comparable to that of a coded aperture device, but with significantly less complexity. As the grid rotates, the transmission from a source is modulated on each detector between 0 and 100%. The count profile is cross-correlated with precalculated modulation profiles to produce an approximate source image. Deconvolution of this image with the known imager response can accurately resolve point sources and complex emissions. The appropriate deconvolution technique can achieve angular resolution better than the basic geometrical resolution of the instrument. A prototype RM developed at Louisiana State University features high sensitivity and energy resolution, functional angular resolution of 15 , and a simple readout system. The detector array consists of 19 1.5 × 1 thick cerium-doped lanthanum bromide (LaBr 3 :Ce) crystals. LaBr 3 produces significantly more light than other common scintillators, offering < 3% FWHM energy resolution at 662 keV. A grid spaced ∼1.2 m from the detection plane with slat width 1.5 offers a 13.8 • field of view. We present our reconstruction technique, deconvolution algorithms, and simulated and experimental imaging results.

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Section: Discussionmentioning

confidence: 97%

Angular resolution obtained with a LaBr 3 -based rotational modulator

2009

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“…A rotating modulator (RM) (Durouchoux et al 1983;Dadurkevicius & Ralys 1985) is one such instrument developed to image hard x-ray and gamma-ray photons (tens of keV to MeV). As we have shown previously (Budden et al 2010b), the RM may have some significant sensitivity advantages over the commonly-used coded aperture, particularly at high energies.…”

Section: Figmentioning

confidence: 78%

“…4, we show examples of count rate profiles generated with the standard and advanced formulae and with Monte Carlo simulations, as well as reconstructed images. The image reconstruction technique has been described elsewhere (Budden et al 2010b), and has been shown to be capable of providing coded-aperture quality resolution with better detector efficiency at high energies, resolving multiple closely-separated sources and operating in the presence of background.…”

Section: Figmentioning

confidence: 99%

“…The algorithm uses an iterative algebraic solution with physical constraints as a form of non-linear regularization and the addition of appropriate randomized noise layers to suppress spurious background. Details of the Noise Compensating Algebraic Reconstruction (NCAR) algorithm are given in Budden et al (2010b). In Budden et al (2010a), it is shown with laboratory measurements that an RM featuring an array of 19 3.8 cm diameter × 2.5 cm thick scintillating detectors (approximately the dimensions a = b = c = 4 cm used in the simulations of Figs.…”

Section: Image Reconstructionmentioning

confidence: 99%

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Characteristic count rate profiles for a rotating modulator gamma-ray imager

Budden

Case

et al. 2011

Astrophys Space Sci

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Rotating modulation is a technique for indirect imaging in the hard x-ray and soft gamma-ray energy bands, which may offer an advantage over coded aperture imaging at high energies. A rotating modulator (RM) consists of a single mask of co-planar parallel slats typically spaced equidistance apart, suspended above an array of circular non-imaging detectors. The mask rotates, temporally modulating the transmitted image of the object scene. The measured count rate profiles of each detector are folded modulo the mask rotational period, and the object scene is reconstructed using pre-determined characteristic modulation profiles. The use of Monte Carlo simulation to derive the characteristic count rate profiles is accurate but computationally expensive; an analytic approach is preferred for its speed of computation. We present both the standard and a new advanced characteristic formula describing the modulation pattern of the RM; the latter is a more robust description of the instrument response developed as part of the design of a wide-field highresolution telescope for gamma-ray astronomy. We examine an approximation to the advanced formula to simplify reconstruction software and increase computational speed, and comment on both the inherent limitations and usefulness of the approach. Finally, we show comparisons to the standard formula and demonstrate image reconstructions from Monte Carlo simulations.

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“…Recent advances in scintillator technology, such as the availability of LaBr3 1 , have opened up a wide range of exciting new possibilities for high-energy astronomy and space science [2][3][4][5] . LaBr3 offers an energy resolution for gamma-ray measurement that is competitive with that of semiconductor detectors while retaining the many strengths of scintillators: simple and reliable implementation, high stopping power, large volume, room temperature operation, and very fast timing.…”

Section: Introductionmentioning

confidence: 99%

Scintillator gamma-ray detectors with silicon photomultiplier readouts for high-energy astronomy

et al. 2013

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Space-based gamma-ray detectors for high-energy astronomy face strict constraints of mass, volume, and power, and must endure harsh operating environments. Scintillator materials have a long history of successful operation under these conditions, and new materials offer greatly improved performance in terms of efficiency, time response, and energy resolution. The use of scintillators in space remains constrained, however, by the mass, volume, and fragility of the associated light readout device, typically a vacuum photomultiplier tube (PMT). Recently developed silicon photomultipliers (SiPMs) offer gains and efficiencies similar to those of PMTs, but with greatly reduced mass and volume, high ruggedness, and no high-voltage requirements. We have therefore been investigating the use of SiPM readouts for scintillator gamma-ray detectors, with an emphasis on their suitability for space-and balloonbased instruments for high-energy astronomy. We present our most recent results, including spectroscopy measurements for lanthanum bromide scintillators with SiPM readouts, and pulse-shape discrimination using organic scintillators with SiPM readouts. We also describe potential applications of SiPM readouts to specific highenergy astronomy instrument concepts.

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Image reconstruction with a LaBr3-based rotational modulator

Cited by 9 publications

References 17 publications

Angular resolution obtained with a LaBr 3 -based rotational modulator

Angular resolution obtained with a LaBr 3 -based rotational modulator

Characteristic count rate profiles for a rotating modulator gamma-ray imager

Scintillator gamma-ray detectors with silicon photomultiplier readouts for high-energy astronomy

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