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Definition of a Twelve-Point Polygonal SAA Boundry for the GLAST Mission.

DE2007915382

Publication Date	2007
Personal Author	Djomehri, S. I.
Page Count	23
Abstract	The Gamma-Ray Large Area Space Telescope (GLAST), set to launch in early 2008, detects gamma rays within a huge energy range of 100 MeV--300 GeV. Background cosmic radiation interferes with such detection resulting in confusion over distinguishing cosmic from gamma rays encountered. This quandary is resolved by encasing GLAST's Large Area Telescope (LAT) with an Anti-Coincidence Detector (ACD), a device which identifies and vetoes charged particles. The ACD accomplishes this through plastic scintillator tiles; when cosmic rays strike, photons produced induce currents in Photomulitplier Tubes (PMTs) attached to these tiles. However, as GLAST orbits Earth at altitudes approx. 550km and latitudes between -26 degrees and 26 degrees, it will confront the South Atlantic Anomaly (SAA), a region of high particle flux caused by trapped radiation in the geomagnetic field. Since the SAA flux would degrade the sensitivity of the ACD's PMTs over time, a determined boundary enclosing this region need be attained, signaling when to lower the voltage on the PMTs as a protective measure. The operational constraints on such a boundary require a convex SAA polygon with twelve edges, whose area is minimal ensuring GLAST has maximum observation time. The AP8 and PSB97 models describing the behavior of trapped radiation were used in analyzing the SAA and defining a convex SAA boundary of twelve sides. The smallest possible boundary was found to cover 14.58% of GLAST's observation time.
Keywords	Astrophysics Gamma rays Telescopes Polygons Charged particles Gamma detection Energy range Radiation detectors Photons Scintillation counters
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Stanford Linear Accelerator Center, CA.; California Univ., Santa Cruz.; Department of Energy, Washington, DC.
Supplemental Notes	Prepared in cooperation with California Univ., Santa Cruz. Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200805
Contract Number	DE-AC02-76SF00515

Definition of a Twelve-Point Polygonal SAA Boundry for the GLAST Mission.

Definition of a Twelve-Point Polygonal SAA Boundry for the GLAST Mission.
DE2007915382

Publication Date	2007
Personal Author	Djomehri, S. I.
Page Count	23
Abstract	The Gamma-Ray Large Area Space Telescope (GLAST), set to launch in early 2008, detects gamma rays within a huge energy range of 100 MeV--300 GeV. Background cosmic radiation interferes with such detection resulting in confusion over distinguishing cosmic from gamma rays encountered. This quandary is resolved by encasing GLAST's Large Area Telescope (LAT) with an Anti-Coincidence Detector (ACD), a device which identifies and vetoes charged particles. The ACD accomplishes this through plastic scintillator tiles; when cosmic rays strike, photons produced induce currents in Photomulitplier Tubes (PMTs) attached to these tiles. However, as GLAST orbits Earth at altitudes approx. 550km and latitudes between -26 degrees and 26 degrees, it will confront the South Atlantic Anomaly (SAA), a region of high particle flux caused by trapped radiation in the geomagnetic field. Since the SAA flux would degrade the sensitivity of the ACD's PMTs over time, a determined boundary enclosing this region need be attained, signaling when to lower the voltage on the PMTs as a protective measure. The operational constraints on such a boundary require a convex SAA polygon with twelve edges, whose area is minimal ensuring GLAST has maximum observation time. The AP8 and PSB97 models describing the behavior of trapped radiation were used in analyzing the SAA and defining a convex SAA boundary of twelve sides. The smallest possible boundary was found to cover 14.58% of GLAST's observation time.
Keywords	Astrophysics Gamma rays Telescopes Polygons Charged particles Gamma detection Energy range Radiation detectors Photons Scintillation counters
Source Agency	Technical Information Center Oak Ridge Tennessee
Corporate Authors	Stanford Linear Accelerator Center, CA.; California Univ., Santa Cruz.; Department of Energy, Washington, DC.
Supplemental Notes	Prepared in cooperation with California Univ., Santa Cruz. Sponsored by Department of Energy, Washington, DC.
Document Type	Technical Report
NTIS Issue Number	200805
Contract Number	DE-AC02-76SF00515