NOVELTY - An intermediate retention chamber (5) is formed between the upper and lower holes (3,4). The total cross section of the flow-path of the upper holes is formed more than the lower hole. The exit of the upper hole is arranged not to oppose with an inlet of the lower hole. The upper holes are formed with pores such that the exit of each pore is arranged in mutually non-opposing position.    USE - For use in slurry precipitate prevention system used in semiconductor manufacturing process, for gas emulsion system and sludge amount reduction system.    ADVANTAGE - The diffusion effect of required capacity is attained by reducing the pressure of fluid flowing from the lower hole. Enables easy diffusion of the injected fluid by forming the cross-section of the flow path of the lower hole less than the upper holes. The clogging of the upper and the lower holes is prevented due to pulverization of the particle contained in the fluid by the diffusion.    DETAILED DESCRIPTION - An intermediate retention chamber (5) is formed between the upper and lower holes (3,4). The total cross section of the flow-path of the upper holes is formed more than the lower hole. The exit of the upper hole is arranged not to oppose with an inlet of the lower hole. The upper holes are formed with pores such that the exit of each pore is arranged in mutually non-opposing position. The upper hole is formed so that the fluid injected to the intermediate retention chamber forms an eddy current at the periphery of the center line of the lower hole. The tip of a projection (6) formed in the inner wall surface of the chamber is positioned near the lower hole. The pressure of the fluid sent to the nozzle is in the range 1 to 50 Mpa.    INDEPENDENT CLAIMS are also included for:    (1) nozzle assembly; and    (2) diffusion method.    DESCRIPTION OF DRAWING(S) - The drawing shows the longitudinal cross-sectional view of a nozzle.    Nozzle (1)    Upper holes (3)    Lower hole (4)    Intermediate retention chamber (5)    Projection (6).