**5. Analytical technique applied on elemental determination**

The neutron activation technique (NA) is based on nuclear properties of the nucleus of the atom, radio- activity, and the interaction of radiation with matter. The simplest description of the technique says that when one natural element is submitted to a neu- tron flux, the reaction (n,γ) occurs. The radionuclide formed emits gamma radiation, which can be meas- ured by suitable equipment. About 70% of the ele- ments have nuclides possessing properties suitable for neutron activation analysis. At the Nuclear Technology Development Centre (CDTN), there is a nuclear reac- tor TRIGA MARK I IPR-R1 that allows the application of this technique [7].

The k0-instrumental neutron activation analysis (k0-INAA,) a variation of NA in which the sample is irradiated without previous chemical preparation was used in this study. This specific method is based on nuclear constants—the k0 factors and some reactor parameters.

Rabbit tissues were irradiated in the reactor TRIGA MARK I IPR-R1. At 150 kW the thermal neutron flux is 6.6 × 1011 neutrons cm2 s–1. The samples were irradiated simultaneously with standards of gold and sodium as comparators, and the reference materials. The elements were determined through three schemes of irradiation: 5 minutes to detect the short half-life radionuclides; 4 hours to detect the medium, and 20 hours, the long half-life radionuclides.

After suitable decay time, the gamma spectroscopy was performed in a HPGe detector, 10% of efficiency, FWHM 1.85 keV and 60Co, 1332 keV, connected to a multichannel analyzer. The calculations were based on the reactor parameters: k0 constants using the Solcoy Sofware ©.
