  This tutorial is devoted to the understanding of the different components
that are present in the neutron light output pulse height distribution of
liquid scintillators in fusion relevant energy ranges. The basic mechanisms for
the generation of the scintillation light are briefly discussed. The different
elastic collision processed between the incident neutrons and the hydrogen and
carbon atoms are described in terms of probability density functions and the
overall response function as their convolution. The results from this
analytical approach is then compared with those obtained from simplified and
full Monte Carlo simulations. Edge effect, finite energy resolution, light
output and transport and competing physical processes between neutron and
carbon and hydrogen atoms and their impact on the response functions are
discussed. Although the analytical treatment here presented allows only for a
qualitative comparison with full Monte Carlo simulations it enables an
understanding of the main features present in the response function and
therefore provides the ground for the interpretation of more complex response
functions such those measured in fusion plasmas. Although the main part of this
tutorial is focussed on the response function to mono-energetic 2.45 MeV
neutrons a brief discussion is presented in case of broad neutron energy
spectra and how these can be used to infer the underlying properties of fusion
plasmas via the application of a forward modelling method.
