  Measurement of the direction of the elastic nuclear recoil track and
ionization charge distribution along it, gives unique possibility for
unambiguous detection of the dark matter WIMP particle. Within current
radiation detection technologies only Time Projection Chambers filled with low
pressure gas are capable of such measurement. Due to the character of the
electronic and nuclear stopping powers of low energy nuclear recoils in the
gas, an asymmetric ionization charge distribution along their tracks may be
expected. Preliminary study of this effect, called Head-Tail, has been carried
out here using the SRIM simulation program for Carbon and Sulfur in 40 Torr
carbon disulfide, as relevant to the DRIFT detector. Investigations were
focused on ion tracks projected onto the axis of the initial direction of
motion in the energy range between 10 and 400 keV. Results indicate the likely
existence of an asymmetry influenced by two competing effects: the nature of
the stopping power and range straggling. The former tends to result in the Tail
being greater than the Head and the latter the reverse. It has been found that
for projected tracks the mean position of the ionization charge flows from
'head' to 'tail' with the magnitude depending on the ion type and its energy.
