  We develop a new hadronic model for GEANT4 that is specialized for the
disintegration of the deuteron by photons, $d\gamma \to n p$. For the
description of two-nucleon interactions, we employ a pionless effective field
theory with dibaryon fields (dEFT). We apply the new model of GEANT4 (G4dEFT)
to the calculations of the total and the differential cross sections in
$d\gamma \to n p$ and compare the results with empirical data. As an
application of the new model, we calculate the neutron yield from the $\gamma +
{\rm CD}_2$ process. G4dEFT predicts peaks for the neutron yield, but the
existing model of GEANT4 does not show such behavior.
