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Abstract  

GaAs is not an ideal matrix for INAA because elements yielding activation products with half-lives up to about 5 d cannot be measured due to the interference by72Ga and76As (t1/2=14.1 h and 26.4 h, respectively). The measurement of radionuclides with longer half-lives is interfered with by74As (t1/2=17.7 d), generated by fast neutrons. However, using an irradiation facility with a very low flux of fast neutrons, in which the generation of74As is minimal, five elements could be determined in GaAs (Cr, Co, Zn, Ag, and Hg). For 27 elements the detection limits were below 1 g/g and for ten of them below 10 ng/g. The determination of nitrogen in GaAs has been carried out using the (n, p)-reaction on14N, which is induced by thermal neutrons. The activation product,14C, can be effectively separated and purified via14CO2 and counted with high efficiency in a liquid scintillation counter, and nitrogen can be determined with fairly low detection limits if sufficiently high neutron fluxes and long irradiation times are applied. The procedure described is based on a reactor irradiation with a thermal flux of 2·1014 n·cm–2·s–1 for 51 days. 0.16±0.09 g/g N in GaAs were determined and the detection limit was about 3 ng/g.

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Abstract  

The results of activation studies of concrete ingredients for shielding structures of nuclear installations in the aspect of their decommissioning are given. It is shown that for the long-lived induced radioactivity of construction mineral materials irradiated for 30 years and cooled for more than one year such radionuclides as calcium, iron, cobalt, caesium and europium are responsible. Elemental content of the binding agent and raw material components for their production is obtained by neutron activation analysis. The results show that the type of the binding agent influences to a great extent the concrete shielding activity. The concentration of the above mentioned elements should be taken into account even at the stage of nuclear power plants design. It would allow one to make a prognosis on the volume and radioactivity of wastes as on the radioactivity effect felt by the staff engaged in the decommissioning.

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Abstract  

By employing neutron (or X-ray) diffraction, the structure of crystalline materials can be determined. However, if an impurity in the crystal is present in concentrations below, say, 1·10–4, its influence cannot be observed in the diffraction patterns. If the impurity present at low concentrations is to be localized, a signal uniquely attributable to the impurity must be obtained. In this paper, two such methods, based on the same principles as the "X-ray standing wave" technique, are proposed for neutrons.

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Abstract  

The facilities for instrumental neutron activation analysis in Delft are described. Technical details of the fast rabbit systems, the normal pneumatic rabbit system, the large sample facility and the various coaxial and well-type Ge-detector spectrometers and sample changers are given. The capacity of the facilities is in the order of 15,000 samples per annum for full multi-element analysis. The capacity of the fast rabbit systems for INAA for use with short half-life radionuclides is even larger. The facilities are accessible for use by scientists from other establishments and countries as well.

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Abstract  

The special features of the Advanced Neutron Source research reactor with planned beginning of construction in 1994 are listed. Pneumatic and beam irradiation facilities will be included and are described in the text of this paper.

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Abstract  

Neutron activation analysis has been applied to determine 12 elements, viz. Na, Mn, As, Fe, Co, Zn, Se, Sc, Cr, Sb, Hf and Ta in high-purity Ga2O3. The first 7 elements could be determined by anion exchange separation and isopropyl ether extraction, and the last 8 elements by instrumental method. It is recommended that the first 3 elements are determine by one of the radiochemical modes and the others by the instrumental method.

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Abstract  

Radiochemical separation methods have been applied for the neutron activation analysis of impurities in four high-purity refractory metals, Ta, Nb, W and Mo. Impurities in the metals of Ta, Nb and W can be separated into groups using anion exchange resin with HF and/or a mixture of HF acid and HCl, but those in Mo is done using both anion and cation exchange resins. The coprecipitation of U with Th in HF media is also investigated.

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Abstract  

A simple preconcentration approach for quantitative separation and determination of traces of rhenium in geological matrix using neutron activation analysis is presented in this work. Anionic species of rhenium were collected on small amounts of anion-exchange resin beads from a large-size geological sample solution followed by neutron irradiation of the resin beads and measurements of rhenium activity for its quantification. ∼200 mg of resin beads were used to concentrate rhenium from 0.5 to 5 gram of the borehole samples. Radioactive tracers of the analyte directly and in the presence of the matrix were used to establish the separation process. During the present work the detection limit of rhenium was found to be 10 ng/g.

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Abstract  

The basic assumptions of activation analysis are that the induced radioactivity is proportional to the amount of analyte, and that the quantity of radioactivity can be related simply to the number of counts observed. Quantitative measurement of activity (and of its uncertainty) is not always simple, especially when accuracy better than a few percent is sought. Recent work with 77Ge and 76As has demonstrated that the accuracy of half-lives in the literature is sometimes insufficient. Despite these and other problems, quantitative understanding and documentation of uncertainties can be accomplished, providing demonstrable quality assurance and supporting claims of traceability to the Système International.

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