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Development of the imaging system of the balloon-borne gamma-ray telescope Máscara Codificada (MASCO)

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6 Author(s)
Braga, J. ; Instituto Nacional de Pesquisas Espaciais (INPE), Divisão de Astrofı´sica, C.P. 515, São José dos Campos, SP, CEP 12201-970, Brazil ; DAmico, Flavio ; Villela, T. ; Mejı a, Jorge
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We report laboratory imaging results of a balloon-borne gamma-ray imaging telescope, Máscara Codificada (Portuguese for “coded mask,”) designed to obtain high angular resolution (∼14 arcmin) images of the sky in the 50 keV–1.8 MeV energy range. The instrument incorporates a coded mask with an aperture pattern based on a 19×19-element modified uniformly redundant array (MURA). This pattern belongs to a subclass of MURAs that are almost completely antisymmetrical for 90° rotations with respect to the lower-right corner of the central element, which allows the implementation of an antimask by a single rotation of the whole mask by 90°. The symmetry properties of the MURAs are discussed. The algorithm for determining the position of the gamma-ray interactions on the instrument’s main detector is described and the results of laboratory tests of the imaging system are presented. The mask–antimask subtraction, applied after a flat-fielding procedure, produced a 60% increase in the signal-to-noise ratio of a strong (∼100σ) point source (662 keV photons coming from a 137Cs radioactive source) image by eliminating systematic distortions in the instrumental background measured over the detector plane. © 2002 American Institute of Physics.

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Review of Scientific Instruments  (Volume:73 ,  Issue: 10 )