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0001 =================================================================
0002 Channeling effect in Geant4
0003 =================================================================
0004 Enrico Bagli - INFN and University Ferrara (Italy)
0005 bagli@fe.infn.it
0006
0007 This example shows how channeling in bent crystal can be simulated
0008 in Geant4
0009
0010 1.INTRODUCTION
0011 The example simulates the channeling of 400 GeV/c protons in bent
0012 Si crystal. Channeling occurs when particles enter a crystal aligned
0013 with atomic planes or axes. In bent crystals, the particles are
0014 trapped between atomic planes and follow the crystal curvature
0015 being deflected. If the particle direction is tangent to a bent
0016 crystal plane is reflected to the opposite direction with respect
0017 to channeling, i.e., it suffer ‘volume reflection’. The example
0018 provides the physical model for planar channeling and volume
0019 reflection in bent crystals.
0020
0021 2.GEOMETRY
0022 The geometry is a bent Si crystal with three Si detectors placed at
0023 -9.998 m, -0.320 m and 10.756 m with respect to the position of
0024 the bent crystal itself. The Si detectors allows to measure
0025 incoming and outgoing angle after the interaction with the Si bent crystal.
0026 The geometry is all under vacuum.
0027
0028 3.PRIMARY EVENT
0029 The primary events are 400 GeV/c protons launched at -10.5 m from the
0030 crystal with 13.36 microrad x 11.25 microrad divergence.
0031
0032 4.PHYSICS
0033 In the example the physics of channeling and volume reflection
0034 has been added to the standard Geant4 physics. The description
0035 of the used model can be found in the paper ‘A model for the
0036 interaction of high-energy particles in straight and bent
0037 crystals implemented in Geant4’ by E. Bagli et al., available
0038 online at http://arxiv.org/abs/1403.5819
0039
0040 5.EXECUTION & OUTPUT
0041 The executable must be run from within the source directory of the example
0042 to ensure that it can find the path for crystal data files.
0043
0044 Data files for Si crystal interplanar potential, nuclei and electron density
0045 are stored in a subdirectory named ’data’
0046
0047 Upon execution, the 2009_PLB680_129.mac macro will automatically run the
0048 example with 1000 protons.
0049
0050 Use
0051 /xtal/setBR XXX 0. 0. m
0052 To change crystal bending to XXX meters
0053
0054 Use
0055 /xtal/setSize 1.0 70. XXX mm
0056 To change crystal length to XXX millimeter
0057
0058 Use
0059 /xtal/potfilename data/Si220pl
0060 To select the (110) Si crystal plane of channeling
0061
0062 GPS commands are used for the primary generator.
0063
0064 The output is the ExExhCh.root file with the TTree ExExChTree
0065 has the leaves:
0066 - angXin : incoming particle X angle at the crystal
0067 - angYin : incoming particle Y angle at the crystal
0068 - posXin : hitting X position of the particle at the crystal
0069 - posYin : hitting Y position of the particle at the crystal
0070 - angXout: outgoing particle X angle out of the the crystal
0071 - angYout: outgoing particle Y angle out of the the crystal
