  We report on a low energy measurement of the ionization yield in a
Tetramethylsilane Time Projection Chamber (TPC) using 2.8 MeV neutrons from a
deuterium-deuterium neutron generator. The proton recoil charge yield is
measured at four different electric fields, finding a dependence that is well
described by the Thomas-Imel model. By comparing the proton recoil yield to
that obtained from $\gamma$-ray calibrations, a quenching factor is obtained
for each electric field. These results demonstrate the feasibility of using
room temperature organic ionisation detectors to detect MeV-scale neutrons in
the proton-recoil channel.
