  Spatial resolution of less than 200 um is challenging for thermal neutron
detection. A novel readout scheme based on the time-projection-chamber (TPC)
concept is used in a gaseous electron multiplier (GEM) detector. Thermal
neutrons are captured in a single 2 um thick Boron-10 converter cathode and
secondary Helium and Lithium ions are produced with a combined energy of 2.8
MeV. These ions have sufficient energy to form straight tracks of several mm
length. With a time resolving 2-dimensional readout of 400 um pitch in both
directions, based on APV25 chips, the ions are tracked and their respective
origin in the cathode converter foil is reconstructed. Using an Ar-CO2 93:7%
gas mixture, a resolution of 100 um (FWHM 235 um) has been observed with a
triple GEM-detector setup at the Garching neutron source (FRMII) for neutrons
of 4.7 Angstrom.
