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The earlier studies made by the ATLAS Radiation Task Force have been reported in ATL-GEN-2005-001. We will use the same geometry, materials, etc as in this report, and compare our FLUGG results with the FLUKA G3/GCALOR results from the Task Force. The agreement is good.
Start-Up for 2009-2010
There is already a very detailed Geant4 description of the ATLAS detector used in physics event simulation; however, it is far too complicated for this application. Instead, we will update the validation geometry to be consistent with the full ATLAS description, concentrating on those regions that affect background the most, e.g.
- Beam line and shielding
- Gap between barrel and toroid
- Cavern outline
We will also add the large missing elements such as
- Barrel toroid
Some simplifications will be made, especially detector internal geometries We will simplify it so that the outlines are correct -- open space between detectors will channel backgrounds and must be simulated properly. We will simplify internal geometries, which are important for detector response but not for this application. It is important to maintain the proper isotopic composition of materials as neutron cross sections are sensitive.
We will calculate the background for each of these changes individually in order to understand their effects.
Expected radiation levels and counting rates will be compared with data after beam turn-on in late 2009 fluences expected for the start-up in late 2009. Predictions will be compared with radiation monitors, detector occupancies and so on. Differences have to be traced back to possible inaccuracies in the modeling.
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