Measurements of fast neutron flux by means of activation of phosphorus.

A method for the measurement of fast neutron flux by phosphorus activation is described. Twenty g of red phosphorus is first evaporated from a large size porcelain boat in a current of nitrogen and the vapor is burned in the flame of a Bunsen burner. During the evaporation, the temperature is raised from about 500 to 600 deg C and, after the phosphorus has disappeared, the temperature is raised to 750 to 800 deg C, depending on the kind of phosphorus used. The sensitivity of the method depends largely on the ashcontent of the phosphorus. A complication is presented by the fact that red phosphorus always contains a measurable quantity of radioactivity. If the best quality phosphorus is used it is possible to detect a continuous flux of fast neutrons (E > 2 Mev) around 20 n/ cm/sup 2/ sec or a single burst around 3 x 10/sup 5/ n/cm/sup 2/. The method has the advantages of being equally sensitive to pulsed neutrons and to a constant flux and of not being disturbed by the presence of gamma rays. (P.C.H.)