Some new techniques have been applied in the determination of relative neutron fluxes in water moderated critical assemblies. Alloy wires of Mn-Fe, In-Al, Au-Al, and U-Zr have been prepared with a high degree of uniformity between individual samples of a given material. Beta activation of these wires is measured by thin scintillation crystals in conjunction with specially stabilized electronics. This procedure results in good “plateaus” of counting rate vs photomultiplier voltage, discriminator setting, and amplifier gain. The counting time of a wire is controlled by a decaying sample of the activated material. Thus, as the counting continues, the counting interval becomes progressively longer, providing automatic decay correction of the data. Several benefits obtain from this method. The statistics of counting for a wire of a given activation level are independent of the time of counting; nonuniform decay (e.g., mixed fission product decay) is handled with the same facility as simple exponential decay. Automatic sample changers are used which make possible the counting of larger numbers of samples (approximately 1500 per day) with a minimum of personnel. These changers have been so adjusted that good precision in positioning is maintained. The automatic features of the counting system permit a rapid qualitative evaluation of the data. An error analysis has been made which indicates an experimental counting error (exclusive of statistical error due to decay) of approximately 0.8%. This error, when combined with the appropriate statistical error, has been applied to improve the use of computer codes in obtaining accurate least square fits of theoretical curves to the experimental data.