class AliGenDeuteron: public AliGenerator

 Afterburner to generate (anti)deuterons simulating coalescence of
 (anti)nucleons as in A. J. Baltz et al., Phys. lett B 325(1994)7.
 If the nucleon generator does not provide a spatial description of
 the source the afterburner can provide one.

 There two options for the source: a thermal picture where all nucleons
 are placed randomly and homogeneously in an spherical volume, or
 an expansion one where they are projected onto its surface.

 An (anti)deuteron will form if there is a pair of (anti)proton-(anti)neutron
 with momentum difference less than ~ 300MeV and relative distance less than
 ~ 2.1fm. Only 3/4 of these clusters are accepted due to the deuteron spin.

 When there are more than one pair fulfilling the coalescence conditions,
 the selected pair can be the one with the first partner, with
 the lowest relative momentum, the lowest relative distance or both.