Imprecision in 14-MeV neutron activation analysis is primarily caused by nonhomogeneity and anisotropy in the usable neutron flux. This fact is considerably magnified in analyses pertaining to short-lived radioactivity such as in the determination of oxygen by 16O(n,p)16N reaction. A design for a variable-speed dual sample rotating assembly is described. This assembly allows reproducible placement of pneumatically injected samples and permits both sample and standard to be exposed to an identical neutron flux as a result of biaxial rotation. The analytical precision, which is now most often limited by the total number of counts accumulated, is about ten times better than that which most standard normalization techniques can provide. The system permits the analyst to determine both neutron and gamma attenuation in dense samples. This irradiation assembly is currently being utilized for the accurate and precise determination of oxygen in NBS Standard Reference Materials. © 1968, American Chemical Society. All rights reserved.