A neutron detector for detecting neutrons includes an exterior shell bounding and sealing an interior volume. The exterior shell serves as a cathode. A central structure extends longitudinally within the exterior shell. The central structure serves as an anode and is maintained at a first voltage. The neutron detector includes an insulating portion extending between the central structure and the exterior shell and longitudinally past a shell end of the exterior shell towards a structure end of the central structure. A guard structure extends circumferentially around an outer insulating surface. The guard structure is positioned on the insulating portion between the shell end and the structure end. The guard structure is maintained at a second voltage such that a leakage current on the outer insulating surface is absorbed by the guard structure. A method of detecting neutrons with the neutron detector is also provided.