Fast and full simulation
In NEXUS there are two main ways of running a simulation: the full and the fast simulation.
In the full simulation scintillation photons and ionization electrons are generated and propagated through the detector, and the sensor response is registered in the output file. While the full simulation is more accurate, it is also very time-consuming and it can be unpractical for high energy events.
In the fast simulation, on the other hand, no scintillation photons, neither ionization electrons are produced and the output file stores only the true information of hits and particles.
Here you can find two examples of configuration files for both cases:
For more information on the parameters of the configuration files you can refer to the slides of the nexus course.