The effects of fast-neutron irradiation and a 6-kG magnetic field on the nuclei spectra and cavitation inception thresholds are examined in water. Nuclei spectra are measured using a light-scattering technique. An acoustic vibratory horn assembly was used for cavitation generation. It was found that fast-neutron irradiation increased the total number of nuclei above ∼4 µm in diameter by ∼1% and decreased the cavitation inception threshold by ∼3%. No measurable effect of the magnetic field was found on either nuclei count (and spectrum) or the cavitation threshold.