  We perform a theoretical study of the scintillation efficiency in the
low-energy region crucial for liquid-xenon dark-matter detectors. We develop a
computer program to simulate the cascading process of the recoiling xenon
nucleus in liquid xenon and calculate the nuclear quenching effect due to
atomic collisions. We use the electronic stopping power extrapolated from the
experimental data to the low-energy region, and take into account the effects
of electrons escaping from the electron-ion pair recombination using the
generalized Thomas-Imel model fitted to scintillation data. Our result agrees
well with the experiments from neutron scattering and vanishes rapidly as the
recoiling energy drops below 3 keV.
