Institution
CDTN/CNEN, Centro de Desenvolvimento da Tecnologia Nuclear / Comissão Nacional de Energia Nuclear (Nuclear Technology Development Center/Brazilian Commission for Nuclear Energy), has started in 1952 in the Engineering School of the Federal University of Minas Gerais – UFMG. It was then named Institute of Radioactive Researches – IPR Instituto de Pesquisas Radioativas). It was the first Brazilian Institution totally involved with the nuclear field. Research of radioactive mineral occurrences, nuclear physics studies, development of metallurgical processes and materials of nuclear interest were some of its first activities. The starting up of the research reactor TRIGA (Training Research Isotope General Atomic) Mark I IPR-R1 was in 1960. It was at that time used to train reactor operators, to carry on several kinds of researches and to produce radioisotopes.
In 1965, after an agreement between the Brazilian National Commission of Nuclear Energy - CNEN and UFMG, IPR became part of the National Plan of Nuclear Energy. From 1972 to 1988 the Institute turned into a research center linked directly to NUCLEBRÁS, a State company in charge of establishing the nuclear industry in Brazil. In 1988, CNEN (Brazilian Commission for Nuclear Energy), a regulatory agency for nuclear energy, started to sponsor CDTN French, American and German cooperation was important in shaping up the cultural profile of CDTN (www.cdtn.br).
Laboratory for Neutron Activation Analysis and the k0-method at CDTN/CNEN
The Laboratory for Neutron Activation Analysis at CDTN/CNEN has developed its activities since the starting up of the TRIGA Mark I IPR-R1 research reactor in 1960.
At that time the need for the determination of natural uranium had just begun in pyrochlore, a niobium ore that would be exported. The X-ray fluorescence and the instrumental neutron activation techniques were then applied to determine the uranium content. The neutron activation technique was applied by means of the delayed fission neutron analysis, the first method to use the reactor as an analytical tool. It was the beginning of uranium ore prospection in Brazil and almost all samples – thousands - collected for about 15 years were analyzed by delayed fission neutrons method. In 1989, around 500,000 uranium determinations were performed. The mineral uranium prospection associated with thorium occurrence increased the need to determine thorium and the application of neutron activation analysis by the comparative method started. There were several opportunities to apply the neutron activation analysis technique.
Nevertheless, in the seventies it was necessary to determine thorium at low levels, ranging from 0.05 to 20 mg L-1 in water and leaching, and 0.05 to 20 mg kg-1 in residues. The instrumental neutron activation analysis that had been applied to determine other elements, started to be applied for Th analysis by measuring 233Th and 233Pa. Radiochemical procedures were introduced afterwards, in order to reduce matrix interference. At the same time, the interest in determining thorium in environmental samples increased. The establishment of the Monitoring Environmental Programs co-ordinated by CDTN in nuclear facilities and mining industries diversified the matrixes to be analyzed: pasture, air filters, biomaterial and food. Other procedures to determine other elements were also developed and applied as routine methods.
In 1995, the k0 instrumental neutron activation analysis, k0-INAA was introduced at CDTN. Tests confirmed that the TRIGA MARK I IPR-RI reactor presented the suitable characteristics to apply the method, mainly due to its stable and homogenous neutron fluxes. In 2003 the method was optimized with the introduction of more suitable software for spectra analysis and elemental concentration.
The k0-method is a quasi-absolute multi-elemental analytical technique, in which instead of standards, neutron flux monitors are used. It is not necessary to submit the sample to any chemical procedure before the analysis and around 200 mg of the sample are enough to perform the determination. Due to the powerful characteristic on elemental concentration determination, this method was set up in routine analytical analysis at CDTN/CNEN producing results with high accuracy and small uncertainties.
Nowadays, the k0-Instrumental Neutron Activation Analysis has been responsible for 90% of the analytical demand of the Laboratory for Neutron Activation Analysis determining several elements (Ag, Al, Au, As, Ba, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Dy, Eu, Fe, Ga, Hf, Hg, Ho, I, K, La, Mg, Mn, Mo, Na, Nd, Rb, Sb, Sc, Se, Sm, Sr, Ta, Tb, Th, Ti, U, V, W, Yb, Zn and Zr) in a large range of concentration μg kg-1 to percentage in several matrixes such as biomaterials (food, plants, yeast, human and animal tissues, medicines, etc.) environmental samples (soil, sediment, water, liquid effluent, airborne particulate matter, etc.) industrial products (alloys, plastic, etc.). In 2006, the Laboratory for Neutron Activation Analysis produced 20,000 results applying the k0-method
