**8. Data applications**

Certified reference materials (rocks, soils, sediments and coals) are used as comparators for the implementation of the technique, and they serve as a basis to compare known quantities of an element with fractions of elements in the sample. Internal standards are used for routine control of the method, and these standards are geological materials with known concentrations reported by other laboratories worldwide that use NAA or other analytical techniques, these standards are evaluated under the same analytical conditions of the

For the determination of uncertainty, the steps recommended in the Reference Guides [23, 24] were followed. First, the measurand was defined, establishing its relation with influence quantities and identifying them. Identifying those with greater contribution were evaluated according to their type: A or B. Finally, the combined uncertainty and the expanded uncer-

The uncertainty estimation was done following the bottom-up approach. The procedure consisted of establishing the measurand, identifying and quantifying the sources of uncertainty and finally determining the combined and extended uncertainties. The sample's mass, standard's mass, neutron flux gradient, counting geometry differences, and sample count statistics were evaluated as sources of uncertainty. Sample and standard count statistics as well as differences in irradiation geometry were identified as the main contributors to the uncertainty [25, 26]. The combined relative uncertainty for the studied elements oscillates between

The results of the evaluation of performance: limits of detection, intermediate precision, robustness, veracity and uncertainty, meet the requirements established for the test method;

> **LOD (mg/ kg)**

**Precision (%)**

**Veracity (%)**

**Uncertainty (%)**

**Energy 2 (keV)**

La La-140 1.68 1596.2 487.0 0.11 6.1 97.4 4.0 Sb Sb-122 2.72 692.8 – 0.05 9.5 103 1.9 U Np-239 2.36 106.1 228.2 0.25 6.9 100 8.9 Ba Ba-131 11.5 216.1 496.3 129 5.1 96.1 8.8 Ce Ce-141 32.5 145.4 – 1.37 2.8 101 9.9 Co Co-60 1925 1173.2 1332.5 0.20 3.2 95.6 5.8 Cs Cs-134 754 604.7 795.9 0.29 2.1 103 6.9 Rb Rb-86 18.6 1076.6 – 10.1 5.8 95.9 6.7 Sc Sc-46 83.8 889.3 1120.5 0.02 3.5 98.3 6.2 Th Pa-233 27.0 312.2 – 0.27 3.3 97.6 8.3

problem samples.

tainties are quantified.

2 and 8% (**Table 2**).

**Element Isotope Half-life** 

**(days)**

**Table 2.** Multi-elemental validation results.

**Energy 1 (keV)**

50 Advanced Technologies and Applications of Neutron Activation Analysis

The Colombian Laboratory for Neutron Activation Analysis, CNAAL, is an installation oriented to the generation of high-quality analytical data that contribute to the geoscientific knowledge of the national territory, represented in the characterization of our valuable mineral and hydrocarbon resources. This potential of CNAAL's analytical technique can now be applied in vast areas of the country, which for decades were the scene of a long, costly and painful armed conflict, which ended in 2016 with the signing of the Peace Agreements between the Colombian State and the FARC guerrillas, the oldest in our continent.

Our laboratory has focused its analytical capabilities on the exploration of rare earth elements, which according to the OECD study [30] present a relatively favorable scenario for the search for these strategic minerals that present a greater supply risk taking into account its typical scarcity.

Rare earth elements (REEs) are central in information and communications technologies and green technologies, which is one of many reasons that justify studies in this area. In this way also, OECD's Cost of Inaction and Resource Scarcity; Consequences for Long-term Economic Growth (CIRCLE) Project "…aims at identifying how feedback from poor environmental quality, climate change and natural resource scarcity are likely to affect economic growth in the coming decades" [28].

Additionally, the characteristic mobility of REE is useful for the study of petrogenetic processes and the study of the geochemical cycle of uranium and other associated energy minerals.

Other applications planned for neutron activation analysis technique are related to: advances in the validation of analytical methods to determine elements, quality assurance by ISO/IEC 17025, continue with successful participation in the IAEA – WEPAL proficiency test and promotes future developments to generate impact researches on selected topics on geological materials characterization (rocks, soils, sediments, minerals and hydrocarbons), forensic sciences (element traces in crime scenes), archeometry (studies of provenance of bones, paintings, pottery, coins) and environmental sciences (mobility and accumulation of eco-toxic elements in humans, from technological and industrial processes and evaluation of environmental impacts in the biotic components), among others. In order to consolidate the credibility of our results, the LAAN has participated in a series of intercomparison exercises whose results have been improved to date.

**References**

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Recent advances in the characterization of the neutron flux (thermal and epithermal) of the modern Colombian nuclear reactor IAN-R1 (upgraded in 2015), allow the CNAAL a window of opportunity for the implementation of the "k0 – NAA method", to improve the analytical capabilities of the laboratory, placing it at the level of other facilities of similar characteristics in other countries [29].
