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Your search keyword '"Madden, Norman W."' showing total 2 results
Start Over Author "Madden, Norman W." Topic gamma ray spectrometry
2 results on '"Madden, Norman W."'

1. A Germanium Orthogonal Strip Detector System for Gamma-Ray Imaging.

Author

Hull, Ethan L., Burks, Morgan T., Cork, Chris P., Craig, William, Eckels, Del, Fabris, Lorenzo, Lavietes, Anthony, Luke, Paul N., Madden, Norman W., Pehl, Richard H., and Ziock, Klaus P.

Subjects
GAMMA ray spectrometry, GERMANIUM diodes, IMAGING systems
Abstract

A coded aperture, germanium-detector based gamma-ray imaging system has been designed, fabricated, and tested. The detector, cryostat, and signal processing electronics are discussed in this paper. The latest version orthogonal strip planar detector is 11-millimeters thick, having 38x38 strips of 2-millimeter pitch. The planar detector was fabricated using amorphous germanium contacts. The strips on each face of the detector lie in a chorded-circular pattern to more efficiently utilize the area of the 10-cm diameter germanium crystal. The detector is held in a mount that allows convenient installation and removal of the detector, lending itself to eventual tiling of such detectors into large arrays. The cryostat includes provisions to install a large volume coaxial germanium detector immediately behind the planar detector in the same cryostat. Many gamma rays Compton scatter from the planar detector into the coaxial detector. The energies of these coincident interactions are summed to increase the gamma-ray detection efficiency for higher energy gamma rays (> 200 keV). This hybrid detector configuration recovers many of the gamma rays that would otherwise scatter out of the planar detector. Each strip is read out with a compact, low noise, external FET preamplifier specially designed for this instrument. A bank of shaping amplifiers, fast amplifiers, and constant-fraction discriminators provide readout information that includes 3-dimensional position information on multiple simultaneous photon interaction positions in the detector at the 2 mm level. The energy deposition at each location is also read out with germanium spectroscopy grade resolution. This information is sent to a computer where the image is formed. The excellent energy resolution of the germanium detector system provides isotopic imaging. [ABSTRACT FROM AUTHOR]

Published
2002

2. The MESSENGER Gamma-Ray and Neutron Spectrometer.

Author

Goldsten, John O., Rhodes, Edgar A., Boynton, William V., Feldman, William C., Lawrence, David J., Trombka, Jacob I., Smith, David M., Evans, Larry G., White, Jack, Madden, Norman W., Berg, Peter C., Murphy, Graham A., Gurnee, Reid S., Strohbehn, Kim, Williams, Bruce D., Schaefer, Edward D., Monaco, Christopher A., Cork, Christopher P., Del Eckels, J., and Miller, Wayne O.

Subjects
GAMMA ray spectrometry, NEUTRONS, DETECTORS, MERCURY (Planet), GEOCHEMISTRY, LOW temperature engineering
Abstract

A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation. The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum for 60Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft, but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort, and a look at some early in-flight data. [ABSTRACT FROM AUTHOR]

Published
2007
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