The indicator radionuclide31Si produced in neutron and deuteron activation analysis for silicon via the reactions30Si(n,) and30Si(d,p), respectively, is specifically separated from the irradiated sample by distillation as31SiF4. In the case of aluminium, the distillation is carried out from a HF(HNO3)H2O2 medium and in the case of molybdenum, niobium, tantalum, titanium and vanadium from a HF/HNO3/HBr/H2SO4 medium. Using liquid scintillation counting, the achievable detection limits for neutron activation analysis are, depending on the type of the matrix, between 4–50 ng/g, and for the deuteron activation analysis of tantalum the detection limit is 5 ng/g.
The sorption of niobium and tantalum on Dowex-1 and open-cell polyurethane foam polyether-type in HF–H2SO4 and HF–HCl medium has been investigated. The mechanism of the sorption as well as the composition of adsorbable complexes is discussed. A selective adsorption of tantalum was achieved from solutions, in which the concentration range of HF was 0.05–2M, of H2SO4
5M and of HCl4M. The most interesting separation possibilities have been tested under dynamic conditions.
Three different methods for pre-irradiation separation of the tantalum matrix combined with preconcentration of trace elements for NAA were developed. They involve selective extraction of tantalum with diantipyrylmethane, and anion- and cation-exchange from hydrofluoric acid medium. The role of the blank as the limiting factor for limits of detection and accuracy was one of the main aspects of this investigation. A conventional radiochemical NAA based on post-irradiation separation of the matrix radionuclides was also applied. The trace elements considered were Ag, Ba, Ce, Co, Cr, Cu, Eu, Hf, K, La, Mn, Mo, Na, Rb, Re, Sc, W, Y, Zn, Zr. The methods were used for the analysis of tantalum materials of different purity grades. The advantages and disadvantages of each technique are discussed and the achievable limits of detection are given.
Authors:H. Münzel, F. Michel, P. Coetzee, and V. Krivan
The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the16O(n, p)16N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons.
It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam
current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen.
In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron
beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about
1010 n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced
fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.