  It is known that scintillation efficiency of organic single crystals depends
on the direction of nuclear recoils relative to crystallographic axes. This
property could be applied to the directional WIMP dark matter detector.
  The scintillation efficiency of carbon recoils in a stilbene crystal was
measured for recoil energies of 30 keV to 1 MeV using neutrons from
$^7$Li(p,n)$^7$Be and $^{252}$Cf. Anisotropic response was confirmed in low
energy regions. The variation of the scintillation efficiency was about 7 %,
that could detect the possible dark matter signal.
