Abstract The design, construction, and performance of a type of sealed 3 He drift tubes for neutron detection are presented. Because the 3 He pressure is in the 25–300 mbar range, the detector costs are not dominated by the 3 He gas. Intrinsic neutron detection efficiencies up to 5% have been observed by using high-density polyethylene moderation. Sensitive measurements of the detector lifetime are achieved by monitoring the full-energy peak of the 3 He(n, p) 3 H reaction as a function of time. The neutron peak position shows a 24-h cycle that may be explained by the physical adsorption of gases onto the wall. The estimated lifetimes of the detectors are sufficiently long and therefore, the design and the construction are robust and practical for applications such as fissile material detection.