Neutron activation analysis of manganese in Japanese iron reference standard materials, with large amounts of manganese

Effects of pile-up and neutron self-shielding were experimentally corrected in INAA of manganese and vanadium in iron and ferro- and silicon manganese samples supplied by the Japan Iron and Steel Federation. A pile-up correction curve was drawn as a function of total gamma count rate for each Ge detector by a 60Co source set at a fixed position and 24Na and 137Cs sources moved to vary the gamma-ray intensities. The neutron self-shielding effect was examined by varying the weight of irradiated samples. The effect was negligible for iron samples containing a few percent manganese when samples of less than 0.2 g were irradiated. Good results were obtained for silicon and ferro-manganese by repeated analyses of samples less than 0.02 g in order to avoid the influence of the neutron self-shielding and sample inhomogeneity. A good result can be also obtained from the maximum point of a quadratic equation derived from the relationship between apparent manganese concentrations and sample weight in the range clearly affected by self-shielding. The water dilution after acid dissolution was also effective for samples of high manganese content if special caution was given to regulate the concentration of chloride having a large neutron absorption cross section.