Delayed-neutron activation analysis at NIST

An automated delayed-neutron activation analysis system has been installed at the NIST research reactor. This work involved characterization of the transfer time of the system, evaluation of blanks, and tests of the system's analytical capabilities through quantitative analysis for uranium in several natural matrix standard reference materials (SRMs). The calibration curve was shown to be linear up to at least 20 mu g of uranium, and the well-thermalized reactor irradiation position makes the system insensitive to thorium and oxygen. For SRMs 1646a Estuarine Sediment and 2710a Montana Soil the values determined for this work agree with the reference and certified values, respectively. The mass fraction of uranium in SRM 695 Multi-Nutrient Fertilizer is the first reported for this material. For this system and the irradiation, transfer, and counting times used, the limit of detection for natural uranium is 20 ng, which corresponds to approximately 200 pg of U-235.