How to: Sources

Sources are the objects that create the primary particles in a simulation. A GATE simulation can contain multiple sources at the same time.

Information about the available sources may be displayed with:

# Print all types of source
print(sim.dump_source_types())

# Print information about all sources
print(sim.dump_sources())

Look at the section Details: Sources in the detailed part of the user guide for a description of all available sources and their parameters.

How to add a source

You can add a to the simulation like this:

sim = gate.Simulation()
# ...
source1 = sim.add_source('GenericSource', 'MyFirstSource')
source2 = sim.add_source('VoxelSource', 'MySecondSource')

How to set the number of primaries

You will obviously want to specify how many primary particles the source should produce. The preferred way to do that is by specifying the activity, i.e. how many particles per time interval are produced. Continuing the example above:

source2.activity = 10 * gate.g4_units.Bq

The total number of particles is given by this activity and the length of the run timing interval(s) of the simulation. Be default, a GATE simulation has one run timing interval that is 1 second long. The source source2 above will therefore produce (about) 10 particles on total. The activity is stochastic so it will be 10 on average.

In simulations with multiple run timing intervals, e.g. in moving geometries, the number of primary particles per run is the source activity times the length of each run timing interval.

Alternatively, you can specify the fixed number of primary particles to be generated, e.g.

source1.n = 100

Note, however, that certain functionality regarding simulations with multiple runs is currently not supported when sources specify the fixed number of particles as above.

How to position the source in space

Geant4 creates primary particles ex nihilo, i.e. out of nothing anywhere in the simulation geometry. It is often convenient, however, to have a source follow a volume, e.g. if the source is actually inside the gantry of a linac in radiotherapy. Therefore, you can attach the source to a volume. For the source2 from above, this would be:

my_gantry = sim.add_volume("BoxVolume", name="my_gantry")
source2.attached_to = my_gantry

Whenver the volume my_gantry moves, the source will move with it.