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lowe-g4

Geant4 version of the low-energy electron scattering model.

Installation

On UNIX systems:

  • Make sure you have CMake (3.3 or higher) installed
  • Install GDML and Xerces-C (see also the GEANT4 installation manual)
  • CLHEP is optional, GEANT4 has its own version included
  • Install GEANT4.10.02 patch 02 with GDML and Xerces-C enabled, a detailed description of this process can be found in the GEANT4 installation manual.
  • The GEANT4 DATA is also necessary, so be sure to install this during the GEANT4 installation.

Before installation, make sure to run the geant4.sh script to setup the right environment variables (this script is placed in the /bin/ in the install directory)

Install the low-energy extension by going into the CADPhysics directory cd CADPhysics and executing:

cmake .
make
make install

repeat this in the SEM directory:

cd ../SEM
cmake .
make
make install

the executable SEM_4.10.00 should now be placed inside the usual installation directory /usr/local/bin or in the /bin/ directory in the specified installation directory.

To run the example, make a symbolic link to the SEM_4.10.00 in the Examples/Transmission directory

cd ../Examples/Transmission
ln -s /usr/local/bin/SEM_4.10.00 SEM

Running a simulation

After the installation, simply execute the following command in the Examples/Transmission:

./run.sh

If the install directory was set to a different directory than the default directory, the environment variable CADPHYSICS_BASE has to be set to the install path INSTALL_DIRECTORY. In this case the example is started by:

CADPHYSICS_BASE=INSTALL_DIRECTORY ./run.sh

This will start a simulation for alumina and a simulation for silicon as can be seen when run.sh is opened in a text editor.

Setting up the simulation parameters

What exactly is simulated can be set in the files present in Examples/Transmission. The sample material can be set in run.sh as mentioned before. In YieldCurve.mac the following can be set:

The amount of primary particles per energy. In the example this is set to 500 in order to have a quick run:

/control/alias NPE 500

The detectors can be set directional or not, if they are directional, the direction has to be set.

/detectors/PlaneR/directional true
/detectors/PlaneR/direction 0.0 0.0 1.0

In the example, the sample itself is also set as a detector, in this case multiple hits is enabled, so that the particles can be tracked inside the sample:

/detectors/Sample/multipleHits true

The primary gun is placed in the geometry:

/gps/pos/centre 0.0 0.0 0.0001 mm

The material of the sample is set to the material given in run.sh:

/detectors/setmaterial LogSample {material}

And at last the energies for which the yield is simulated are set. The energy has to be given in eV:

/control/foreach mac/energy.mac energy 1250

Note that in the expample only one energy is given, if multiple energies are desired e.g. 500, 1000 and 1500 eV:

/control/foreach mac/energy.mac energy 500 1000 1500

The simulation geometry is defined in BulkSample.gdml and YieldCurve.gdml. In BulkSample.gdml first the solids are defined, then the logical volumes are defined using the already defined solids. Then the logical volumes are placed in the samplecontainer and the physical volumes are defined. The geometry in the example consists of a 500 nm thick membrane as sample with two detectors. One detector is placed above the sample, the reflection detector and one detector is placed below the sample, the transmission detector. Note that the top of the sample is at 0.0 on the z-axis, which means the primary gun is positioned above the sample in YieldCurve.mac. In YieldCurve.gdml the samplecontainer is placed inside the World volume and the list of detectors is defined.

In the mac directory, two more mac files are present, Pointsource.mac and energy.mac. In Pointsource.mac the particle source is setup. energy.mac sets up the energy of the gun, not that here the energies from YieldCurve.mac are used. It is also possible to set an energy window of the detectors (commented out in the example) The output files are also se in energy.mac. In the example, the yields of the reflection and transmission detector are set as output as well as the hits for both detectors and the sample. The hits of the sample can be used to reconstruct all electron tracks. If this is not necessary, the line

/detectors/Sample/outputHits {directory}/EmissionSample_{material}_{energy}.dat

can be commented out. In this case, the sample can also be removed from the detectorlist in YieldCurve.mac.