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0001 \page Examplech0 Example ch0
0002
0003 \author Enrico Bagli - INFN and University Ferrara (Italy) \n
0004 bagli@fe.infn.it
0005
0006 This example shows how channeling in bent crystal can be simulated
0007 in Geant4
0008
0009 ## INTRODUCTION
0010
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 ## GEOMETRY
0022
0023 The geometry is a bent Si crystal with three Si detectors placed at
0024 -9.998 m, -0.320 m and 10.756 m with respect to bent crystal position.
0025 The Si detectors allows to measure incoming and outgoing angle
0026 after the interaction with the Si bent crystal. The
0027 geometry is all under vacuum.
0028
0029 ## PRIMARY EVENT
0030
0031 The primary events are 400 GeV/c protons at -10.5 m from the
0032 crystal with 13.36 microrad x 11.25 microrad divergence.
0033
0034 ## PHYSICS
0035
0036 In the example the physics of channeling and volume reflection
0037 has been added to the standard Geant4 physics. The description
0038 of the used model can be found in the paper ‘A model for the
0039 interaction of high-energy particles in straight and bent
0040 crystals implemented in Geant4’ by E. Bagli et al., available
0041 online at http://arxiv.org/abs/1403.5819
0042
0043 ## EXECUTION & OUTPUT
0044
0045 The executable must be run from within the source directory of the example
0046 to ensure that it can find the path for crystal data files.
0047
0048 Data files for Si crystal interplanar potential, nuclei and electron density
0049 are stored in a subdirectory named ’data’
0050
0051 Upon execution, the macro `2009_PLB680_129.mac` will automatically run the
0052 example with 1000 protons.
0053
0054 Use
0055 ```
0056 /xtal/setBR XXX 0. 0. m
0057 ```
0058 To change crystal bending to XXX meters
0059
0060 Use
0061 ```
0062 /xtal/setSize 1.0 70. XXX mm
0063 ```
0064 To change crystal length to XXX millimeter
0065
0066 Use
0067 ```
0068 /xtal/setEC data/Si220
0069 ```
0070 To select the (110) Si crystal plane of channeling
0071
0072 GPS commands are used for the primary generator.
0073
0074 ### ExExhCh.root
0075
0076 The output is the ExExhCh.root file with the TTree ExExChTree
0077 has the leaves:
0078 - angXin : incoming particle X angle at the crystal
0079 - angYin : incoming particle Y angle at the crystal
0080 - posXin : hitting X position of the particle at the crystal
0081 - posYin : hitting Y position of the particle at the crystal
0082 - angXout: outgoing particle X angle out of the the crystal
0083 - angYout: outgoing particle Y angle out of the the crystal
