**7. Quality assurance**

The subscripts indicate parameters for the unknown sample and the comparator or standard. That is, the mass fraction of the unknown sample of the element (measurand) and the mass fraction of the element in the reference material. W is the total mass of the samples. The number of net counts of the energy of interest (keV) and the counting time of the gamma radiation are decay correction factors of the peak; this factors are used to obtain the neutron flux correction factor, which quantify the gradient of the flux between the irradiation position of the

The neutron flux correction factor is determined as the ratio between the flux measured with the 0.1% Au-Al flux monitors at the sample position and that of the comparator. The neutron flux is proportional to the number of counts in energy range of 198Au and depends on other factors such as the neutron capture cross-section, isotope abundance, irradiation time, 198Au half-life, detection efficiency, and number of accounts for the emission energy of the radioactive isotope. Taking the relationship between the flux readings, all the terms except for the number of counts registered for the monitor at the sample position and for the monitor at the

This relationship is fulfilled, assuming that the irradiation conditions and counting geom-

In compliance with national regulations, the Neutron Activation Analysis Laboratory has developed a simple scheme for the safe management of activated samples once they are no longer needed. These procedures are authorized and monitored by the National Nuclear Authority (Ministry of Mines and Energy). The aim of radioactive waste management is to isolate and apply protective measures to this type of waste so that there are no foreseeable

Most of the radioactive waste corresponds to plastic materials (vials, racks, bags, tapes, etc.), as well as flux monitors and samples activated during irradiation, and also elements used in the decontamination of working areas (gloves, paper towels, plastic bags, etc.). Most of the waste is classified into three categories: Group 1 – Exempt Waste (EW), Group 2 – Very Short-

The NAA Lab has a decay room for the temporary storage of VSLW, equipped with the necessary shielding and equipment for its safe handling. The room is locked and permanently monitored, admission is restricted to non-operating personnel, unless authorized otherwise.

In order to classify and monitor temporarily stored waste, packages are analyzed by gamma spectrometry. Each package is analyzed separately in the GC-7020 detector at a reading geometry of 10 mm during 4 h, determining the activity of each of the radionu-

future human health risks and/or negative effects on the environment.

Lived Waste (VSLW) and Group 3 – Very Low Level Waste (VLLW) [16].

The stored waste is properly labeled and grouped into packages each workweek.

sample and the comparator.

etries are similar.

clides present.

comparators position are canceled, obtaining:

48 Advanced Technologies and Applications of Neutron Activation Analysis

**6. Radioactive waste disposal**

As part of the validation process for NAA using HPGe detectors and future accreditation of the laboratory under ISO/IEC 17025:2005 [21], the technique has been validated for the determination of rare earths such as La and Ce, and elements of interest such as U and Th in geological matrices. The following parameters were taken into account: selectivity, linearity, reproducibility, limits of detection and quantification, robustness and uncertainty estimation.

This process included the evaluation of detection limits and quantification of gamma radiation spectra obtained, according to the statistical criterion of Currie [22]. The following results show element concentrations in the sample in units of mg/kg. Ba: 129, Ce: 1.37, Co: 0.20, Cs: 0.29, La: 0.11, Rb: 10.06, Sb: 0.054, Sc: 0.024, Th: 0.27, U: 0.2. These results were comparable to those reported by other laboratories, thus demonstrating the competence of the NAA Laboratory on multielemental analysis in geological matrices.

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 problem samples.

establishing a line of work toward further validation of more elements and offering the scien-

Colombian Neutron Activation Analysis Laboratory (CNAAL): Applications and Development…

http://dx.doi.org/10.5772/intechopen.74395

51

As part of the application for the accreditation process under the ISO/IEC-17043 standard [29], and the need for constant validation in performance and quality assurance, the laboratory participates in annual IAEA-WEPAL (Wageningen Evaluating Programmes for Analytical Laboratories) Proficiency Tests and Inter-laboratory Comparisons, obtaining excellent results and positioning its metrological competence, this being a major step toward accreditation

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

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

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

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

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

between the Colombian State and the FARC guerrillas, the oldest in our continent.

tific community a proven method according to international standards [27].

under ISO/IEC 17025 [21].

**8. Data applications**

typical scarcity.

minerals.

the coming decades" [28].

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 uncertainties are quantified.

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

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


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

establishing a line of work toward further validation of more elements and offering the scientific community a proven method according to international standards [27].

As part of the application for the accreditation process under the ISO/IEC-17043 standard [29], and the need for constant validation in performance and quality assurance, the laboratory participates in annual IAEA-WEPAL (Wageningen Evaluating Programmes for Analytical Laboratories) Proficiency Tests and Inter-laboratory Comparisons, obtaining excellent results and positioning its metrological competence, this being a major step toward accreditation under ISO/IEC 17025 [21].
