Quenching and Channeling of Nuclear Recoils in NaI[Tl]: Implications for
  Dark Matter Searches
  A new experimental evaluation of the quenching factor for nuclear recoils in
NaI[Tl] is described. Systematics affecting previous measurements are addressed
by careful characterization of the emission spectrum of the neutron source, use
of a small scintillator coupled to an ultra-bialkali high quantum efficiency
photomultiplier, and evaluation of non-linearities in the electron recoil
response via Compton scattering. A trend towards a rapidly diminishing
quenching factor with decreasing sodium recoil energy is revealed.
Additionally, no evidence for crystal lattice channeling of low-energy
recoiling ions is found in a scintillator of known crystallographic
orientation. A discussion on how these findings affect dark matter searches
employing NaI[Tl] (e.g., DAMA/LIBRA) is offered.
