Computer simulation
Past group member Steve Rodney has done some preliminary experimentation with a small model and computer simulation of a fixed point source and filamentary sources. A 1-dimensional URA mask with multiple passes is proved to be just as effective as a 2-dimensional mask in gathering 2-D information of the source. Since a 1-D mask is much easier to construct, our current physical model is a 1-D URA mask constructed by Steve Rodney.
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Point source |
Filament |
Small-scaled model
To simulate X-ray objects that will be observed by Constellation-X, we placed a 1mCi Cs-137 (peak energy at 662keV) 2.5 meters away from a 2" NaI detector, with the occulting mask 60cm away from the detector. Currently the Cs-137 source is mounted onto a spinning wooden disc to simulate a circular ring source. The occulting mask is in a pattern of half transparent, half opaque Uniformly Redundant Arrays (URA) to compromise between photon collection and resolution. We run 4 passes of the mask to collect 2-dimensional information of the source. Because we cannot rotate the mask freely as we would in space, the source setup is rotated instead.
The dark circle is the detector point of view projected onto the mask, the black star is the source behind the mask. To simulate the mask moving at a clockwise 45 degree in a passing, we move the source to the lower lefthand corner; to simulate the mask moving at counterclockwise 45 degree, we place the source to the upper lefthand side.
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Source setup |
Mask setup |
The image reconstruction process is a modified version of the eclipse mapping method (EMM) and it makes use of coded aperture imaging to reduce background and noise. Reconstruction of the current setup is in process and other configurations will be constructed and explored next.
Below is a data set of 5 experiment runs. The photon count rates dipped whenever the opaque part of the mask passed in front of the source.
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count rates data set |
Preliminary Image Reconstruction |
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