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1 =================================================================
2 Channeling effect in Geant4
3 =================================================================
4 Enrico Bagli - INFN and University Ferrara (Italy)
5 bagli@fe.infn.it
6
7 This example shows how channeling in bent crystal can be simulated
8 in Geant4
9
10 1.INTRODUCTION
11 The example simulates the channeling of 400 GeV/c protons in bent
12 Si crystal. Channeling occurs when particles enter a crystal aligned
13 with atomic planes or axes. In bent crystals, the particles are
14 trapped between atomic planes and follow the crystal curvature
15 being deflected. If the particle direction is tangent to a bent
16 crystal plane is reflected to the opposite direction with respect
17 to channeling, i.e., it suffer ‘volume reflection’. The example
18 provides the physical model for planar channeling and volume
19 reflection in bent crystals.
20
21 2.GEOMETRY
22 The geometry is a bent Si crystal with three Si detectors placed at
23 -9.998 m, -0.320 m and 10.756 m with respect to the position of
24 the bent crystal itself. The Si detectors allows to measure
25 incoming and outgoing angle after the interaction with the Si bent crystal.
26 The geometry is all under vacuum.
27
28 3.PRIMARY EVENT
29 The primary events are 400 GeV/c protons launched at -10.5 m from the
30 crystal with 13.36 microrad x 11.25 microrad divergence.
31
32 4.PHYSICS
33 In the example the physics of channeling and volume reflection
34 has been added to the standard Geant4 physics. The description
35 of the used model can be found in the paper ‘A model for the
36 interaction of high-energy particles in straight and bent
37 crystals implemented in Geant4’ by E. Bagli et al., available
38 online at http://arxiv.org/abs/1403.5819
39
40 5.EXECUTION & OUTPUT
41 The executable must be run from within the source directory of the example
42 to ensure that it can find the path for crystal data files.
43
44 Data files for Si crystal interplanar potential, nuclei and electron density
45 are stored in a subdirectory named ’data’
46
47 Upon execution, the 2009_PLB680_129.mac macro will automatically run the
48 example with 1000 protons.
49
50 Use
51 /xtal/setBR XXX 0. 0. m
52 To change crystal bending to XXX meters
53
54 Use
55 /xtal/setSize 1.0 70. XXX mm
56 To change crystal length to XXX millimeter
57
58 Use
59 /xtal/potfilename data/Si220pl
60 To select the (110) Si crystal plane of channeling
61
62 GPS commands are used for the primary generator.
63
64 The output is the ExExhCh.root file with the TTree ExExChTree
65 has the leaves:
66 - angXin : incoming particle X angle at the crystal
67 - angYin : incoming particle Y angle at the crystal
68 - posXin : hitting X position of the particle at the crystal
69 - posYin : hitting Y position of the particle at the crystal
70 - angXout: outgoing particle X angle out of the the crystal
71 - angYout: outgoing particle Y angle out of the the crystal