  A new data-based charge exchange model of GEANT4 dedicated to the
$^{9}$Be(p,n)$^{9}$B reaction is developed by taking the ENDF/B-VII.1
differential cross-section data as input. Our model yields results that are in
good agreement with the experimental neutron yield spectrum data obtained for
proton beams of energy $(20\sim35)$ MeV. In particular, in contrast to all the
considered GEANT4 hadronic models, the peak structure resulting from the
discrete neutrons generated by the charge-exchange reaction is observed to be
accurately reproduced in our model.
