Wear measurement at depths of several tens micrometers on the surface of iron using a thin layer activation method by 7 MeV proton beam

A method of measuring iron wear using thin layer activation is discussed. The iron surface is activated by a 56Fe(p, n)56Co reaction etc. using a 7.00 MeV proton beam from a tandem Van de Graaff accelerator. Irradiation of 0.5-2 μA beam currents produces 1-10 μCi of 56Co activities in a layer about 50 μm thick. To get the basic depth profile of cobalt activities, a 1.5 cm iron cube with a 3 mm diameter activation area is used to produce a wear calibration curve. Wear is produced by a polishing machine and wear thickness is measured by a precise electric micrometer. Monitoring radiation instruments are a 3 in. diameter x3 in. NaI (Tl) scintillator and a high-purity Ge detector. A detailed iron wear calibration curve using 56Co, 57Co and 58Co activities is obtained in accordance with iron weak thickness. After discussion, a universal iron wear calibration curve using the 56Co/57Co or 56Co/58Co ratio is newly developed. This convenient curve is expressed in an experimental formula with a correction for time attenuation. (orig.)