| Geant4 Cross Reference |
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