7. Conclusions

The Laboratory for Neutron Activation Analysis at CDTN, Brazil, needs to be prepared to meet customer analysis requirements. In order to answer this requirement, it was necessary to establish a methodology to analyse large samples, from 0.5 to 5 g sample, applying the k0 standardised method keeping the current infrastructure for irradiation and gamma measurements. Another objective was to overcome technical limitations while analysing samples smaller than 0.5 g, as, for instance, inhomogeneity of the sample and lower thermal neutron flux of the reactor.

To carry out the establishment, it was necessary to calculate several relevant parameters that would point out the feasibility to analyse large samples: detector efficiency over the volume source, neutron self-shielding during neutron irradiation and gamma-ray attenuation within the sample during counting.

The results [16, 36, 37] pointed out that all parameters may be negligible for the large sample. At least, within the uncertainty range, once the elemental concentration results are in good agreement with the recommended values of the reference material IAEA-SOIL-7. All results obtained during the development using the reference material were evaluated by the statistical test, En-score, which pointed out that the k0-method applied using KayWin software presented an overall satisfactory performance. Few exceptions are already being investigated using other reference materials. It means that the KayWin software proved to be a robust programme to calculate the elemental concentration of large samples producing reliable results.

It is important to note that once the methodology is established, the following benefits may be obtained: reaching lower limits of detection; enabling compliance, for example, in environmental legislation in determining the concentration of metals in soil; analyses of more representative aliquots, especially in the case of non-homogeneous samples, as industrial waste; optimization of the cost and time of analysis, because instead of analysing several small samples they could be replaced by a large sample; analyses of whole parts when removing the aliquots are not possible. This study is still going on in order to confirm the benefits that have been already mentioned.

This investigation has confirmed that any other laboratory applying k0-instrumental neutron activation analysis (k0-INAA) is able to establish this methodology without having to modify its facilities, since the neutron self-shielding, gamma attenuation and detector efficiency over the volume sample are established.
