The White Sands Missile Range Fast Burst Reactor (FBR) is

an unmoderated, unreflccted bare critical assembly of the Godiva II type. The FBR is extensively used for producing a nuclear environ-ment which stimulates the neutron portion of a nuclear weapon (>). Military systems are exposed to this environment for testing and analysis of their response to a nuclear weapon. The primary system degradation at tne FBR is produced by neutron interactions within the system. Most of the military systems tested use solid state electronic devices. Neutron displacement and other neutron effects in the silicon devices cause the electronic degradation. The amount of damage produced by a neutron is a function of the neutron energy. The neutrons produced by the FBR have a continuous (fission) spectrum of energies. A complete characterization of this spectrum is essential in the evaluation of the nuclear effects on the system under evaluation.^ Because neutron spectra are of such wide interest, numerous methods have been investigated for their measurement. Nuclear emulsions have been used successfully, but the method is limited by tedious data analysis and low sensitivity (2). Spectro-meters consisting of a 'sandwich ' of "Li or ^He between two surface barrier or gas proportional detectors have proven useful in both fast and thermal neutron environments (3), (4), (5) However, radiation damage to the solid state detectors and high level gamma intensities are a serious problem (6). Proton