Uncertainty Budget for k0-NAA

The concepts of the Guide to the expression of Uncertainties in Measurements for chemical measurements (GUM) and the recommendations of the Eurachem document "Quantifying Uncertainty in Analytical Methods" are applied to set up the uncertainty budget for k ₀-NAA. The "universally applicable spreadsheet technique", described by Kragten, is applied to the k ₀-NAA basic equations for the computation of uncertainties. The variance components — individual standard uncertainties — highlight the contribution and the importance of the different parameters to be taken into account.     

k0 and Comparator NAA: Influences and Interactions

A discussion is held on mutual influences and interactions between k ₀- and (relative) comparator-type NAA. Examples are given concerning: (1) the application of comparator-type NAA in the quality control/quality assurance of the IRMM-530 Al-0.1%Au neutron flux monitor developed for use in k ₀-NAA, (2) the utilization of the k ₀-method of calibration as a tool for the quality assurance of comparator-type NAA, (3) the introduction of corrections for detection efficiency and true-coincidence (of primordial importance in k ₀-NAA) in comparator-type NAA, (4) the development of k ₀-type standardization for use in prompt gamma neutron activation analysis, and (5) the renewal of insights in the traceability of k ₀- and comparator-type NAA.     

The application and development of k0-standardization method of neutron activation analysis at Dalat research reactor

In recent years the k ₀-NAA method has been applied and developed at the 500 kW Dalat research reactor, which includes (1) the establishment of a PC database of k ₀-NAA-related nuclear parameters, e.g., radionuclide produced, half-lives, k ₀-factors, Q ₀, _r, E _g, etc; the access to the database is able by a k ₀-NAA software or by manual; (2) the detection efficiency calibration of gamma spectrometers used in k ₀-NAA, (3) the determination of reactor neutron spectrum parameters such as a and f factors and neutron fluxes in the irradiation channels, and (4) the validation of the developed k ₀-NAA procedure by analysing some SRMs, namely Coal Fly Ash (NIST-1633b), Bovine Liver (NIST-1577b) and IAEA-Soil7. The analytical results showed the deviations between experimental and certified values were mostly less than 15% with most Z-scores lower than 2. The k ₀-NAA procedure established at the Dalat research reactor has been regarded as a reliable standardization method of NAA and as available for practical applications, in particularly for airborne particulate and crude oil samples.     

Establishment of the k 0, \bar{E}_{\rm r}, Q 0, and cascade coincidence correction factors for the determination of 129I by k 0-NAA

A k ₀-NAA procedure used in the determination of ¹²⁹I is established. For this purpose, the k ₀-values for the reaction ¹²⁹I (n, ??) ¹³⁰I are determined, the Q ₀- and $\bar{E}_{\rm r}$ -values are calculated, and the correction procedure for the cascade coincidence effects is established by calculation of the correction factor COI for five ¹³⁰I ??-rays (418.0, 536.1, 668.5, 739.5, and 1157.5 keV).     

The robustness of k 0-NAA in large multi-purpose research reactors

The challenges and opportunities associated with performing k ₀-NAA in high-powered, multi-purpose research reactors are examined and recommendations are made concerning the conditions that need to be met in such facilities in order to allow the potential for this method of elemental analysis to be fully realised.     

Quality assessment on airborne particulate matter of k0-INAA

The analysis of airborne particulate matter (APM) by k ₀-NAA was assessed using: (1) BCR reference material (RM) simulated air-filters, (2) synthetic air-filters prepared by spiking blank filters with standard solutions, and (3) real APM filters. k ₀-INAA is a suitable technique for the analysis of APM, delivering accurate and precise results. However, the quality assessment of APM analysis appears to be a difficult task.     

Calibration of the B54X channel and implementation of k 0-NAA at the RA3-reactor,Ezeiza, Argentina

The B54X position of the 8 MW RA3 research reactor at the Ezeiza Atomic Centre of the Argentine National Atomic Energy Commission is currently being used for NAA irradiations. The facility with a nominal average fluence of 5 × 10¹³ cm^?2 s^?1 is dedicated to long irradiations of up to 5 h. Samples are being measured after a decay of typically 7 and 30 days. With the aim of implementing the k ₀-NAA method at the Nuclear Analytical Techniques Laboratory of the Centre, the reactor parameters α and f were estimated applying multi monitor methods using the Kayzero for Windows software. After a careful recalibration of the HPGe detector, SMELS III, NIST SRM 1633b and several other matrix RM’s were analyzed using the k ₀ standardization in order to verify the proper implementation of the k ₀-NAA approach. The found accuracy and associated uncertainties are discussed. In general, good agreement was obtained between results of this work and the reference values of the individual reference materials, thus proving successful first implementation of the above method and trueness of the results achieved. The obtained detection limits for several elements were evaluated.     

A Web tool for calculating k0-NAA uncertainties

The calculation of uncertainty budgets is becoming a standard step in reporting analytical results. This gives rise to the need for simple, easily accessed tools to calculate uncertainty budgets. An example of such a tool is the Excel spreadsheet approach of Robouch et al. Here, we present an internet application which calculates uncertainty budgets for k ₀-NAA. The Web application has built in Literature values for standard isotopes and accepts as inputs fixed information such as the thermal to epithermal neutron flux ratio, as well as experiment specific data such as the mass of the sample. The application calculates and displays intermediate uncertainties as well as the final combined uncertainty of the element concentration in the sample. The interface only requires access to a standard browser and is thus easily accessible to researchers and laboratories. This may facilitate and standardize the calculation of k ₀-NAA uncertainty budgets.     

Neutron flux characterization of the Moroccan Triga Mark II research reactor and validation of the k 0 standardization method of NAA using k 0-IAEA program

The aim of this work was to implement and to validate the k ₀ standardization method in neutron activation analysis (k ₀-NAA) at the Moroccan TRIGA Mark II research reactor. This technique was used in order to determine, the calibration of several HPGe detectors and calibration of neutron flux parameters in the typical irradiation channels [rotary specimen rack (RSR) and the pneumatic tube system (PTS) facilities]. Calibrations and calculations of k ₀-NAA results were carried out using the k ₀-IAEA program. The two parameters of neutron flux in the selected irradiation channels used for elemental concentration calculation, f (thermal-to-epithermal ratio) and α (deviation from the 1/E distribution), have been determined as well in the PTS as in the RSR facilities using the zirconium bare triple method. Results obtained for f and α in two irradiation channels show that f parameter determined in this way is different in the RSR and the PTS facilities. This can be explained by the fact that the RSR channel is situated in a graphite reflector and is relatively far from the reactor core, while the PTS is in the core. Five reference materials of different origin obtained from USGS (basalt BE-N, bauxite BX-N, biotite mica-Fe, granite GS-N) and IAEA (Soil-7) were used to evaluate the validity of this method in our laboratory by analyzing the elemental concentrations with respect to the certified values. In general, good agreement was obtained between results of this work and values in certificates of the individual reference materials, thus proving the accuracy of our results and successful implementation of the method for analysis of real samples.     

Overall measurement uncertainty of k0-based neutron activation analysis

Summary Special aspects of the uncertainty quantification in k₀-NAA are discussed and applied in accordance with the Guide to the Expression of Uncertainty in Measurement (GUM), on a model case. The uncertainty budget is calculated highlighting the contribution and the importance of the different parameters to be taken into account. The importance of the nuclide-specific and neutron fluence-specific approach in estimating individual uncertainty contributions is emphasized and demonstrated by examples of Au, Cr, Rb, and Sb determinations.     

Characterization of pneumatic fast transfer system irradiation position of KAMINI reactor for k 0-based NAA

The pneumatic fast transfer system position at KAMINI reactor, Indira Gandhi Centre for Atomic Research, India was characterized by determining the epithermal neutron flux shape factor (α) and the sub-cadmium to epithermal neutron flux ratio (f) for k ₀-based Neutron Activation Analysis (k ₀-NAA). For determination of α value, bare, Cd-ratio and Cd-cover methods were employed using dual and multi monitors namely Au, Zr and Zn. For calculation of f, Au and Zr monitors were used in the case of bare method and Au monitor was used for cadmium ratio and cadmium cover methods. The determined α-value of PFTS indicated a hard epithermal neutron spectrum and the f value indicated about 96 % thermal neutron component. For validation of k ₀-NAA method, reference materials namely NIST SRM 1646a (Estuarine Sediment) and BCS Nb-stabilized Stainless Steel (BCS/SS No.261/1) were analyzed. The percentage errors of the determined concentration values of elements were within ±5 % with respect to the certified values and the Z-score values at 95 % confidence level were within ±2 in most of the cases.     

Comparison of 14 MeV-NAA, k0-NAA and ED-XRF for air pollution bio-monitoring

In this paper the performances and the limitations of three multi-elementary analysis techniques are compared applied to a study of air pollution biomonitoring in Morocco. These techniques are: (1) 14 MeV neutron activation analysis (14 MeV-NAA), (2) thermal neutron activation analysis using the k ₀ quasi-absolute method (k ₀-NAA) and (3) energy dispersive X-ray fluorescence analysis (ED-XRF). The experimental procedures and the control of the analytical results using certified reference materials are described and discussed. The three methods were confronted for the analysis of lichens, mosses and tree-barks. The complementarity of these methods enabled us to determine 43 elements in different samples. The most suitable method for each element was selected according to the sensitivity and selectivity necessitating the minimum corrections of the matrix effects and/or the interfering reactions.     

Measurement of k 0 and Q 0 values for iridium isotopes

There is an increasing demand for the chemical analysis of new materials containing iridium. The k ₀-method is an excellent method for the analysis of new materials but measured k ₀-values and Q ₀-values have been lacking for ¹⁹¹Ir(n,γ)¹⁹²Ir, which offers greater sensitivity than ¹⁹³Ir(n,γ)¹⁹⁴Ir. In this work, the Q ₀-values were determined for the two reactions by the two-channel method, using five irradiation channels in two research reactors in Belgium and Canada. These measured Q ₀-values enabled the first determination of the resonance neutron Cd transmission factors for these two capture reactions, confirming suspicions that they are much less than unity. At the two laboratories, k ₀-values were measured for ¹⁹²Ir and ¹⁹⁴Ir and there was good agreement between the two laboratories. The k ₀-values for ¹⁹²Ir are original measurements, while those for ¹⁹⁴Ir are in good agreement with previously published values.     

Determination of 237Np by k0 RNAA

The determination of very low concentrations of ²³⁷Np is of key-interest for environmental monitoring. The application of the k ₀-method to neutron activation analysis was not possible so far, since the k ₀-parameters were lacking. The parameters required for the k ₀-method are: the effective resonance energy r, the resonance integral (1/E) to 2200 m^.s^-1 cross section ratio Q ₀, and the k ₀ values. In this work, the experimental values of these parameters were determined by using two nuclear reactors with very different flux characteristics.     

Bronze analysis by k0-NAA and PIXE

Five copper alloys were prepared with modern powder metallurgical processes in the frame of the European project Improvement of Means of Measurement on Archaeological Copper-Alloys for Characterisation and Conservation (IMMACO) and certified for As, Pb, Sn and Zn mass fractions. Similar in their composition to archaeological bronze alloys, these Certified Reference Materials (CRMs) are to be used for calibration of XRF instruments for characterization of archaeological samples either in the laboratory or in the field. This paper presents and compares the successful contribution of our non-destructive analytical methods (k ₀-NAA and PIXE) to the IMMACO project and to the certification of the five reference materials.     

The preparation and homogeneity study of synthetic multi-element standards (SMELS) for QC/QA of k0-NAA

Three new synthetic multi-element standards (SMELS) were developed for testing the performance of the k ₀-standardization neutron activation analysis (k ₀-NAA) method when implemented in a laboratory. SMELS consist of a phenol-formaldehyde polymer matrix spiked with different groups of elements according to the half-lives of the formed radionuclides. They are classified as Type I for short-, Type II for medium- and Type III for long-lived radionuclides. This article presents the preparation of SMELS including different aspects such as choice of the matrix and spiking elements, chemical compounds, target concentrations, purity of the matrix and spiking procedure and the homogeneity study for all the spiked elements in order to demonstrate the quality of the produced materials.     

Determination of Q 0 and k 0 factors for 75Se

Since the initial determination of the Q ₀ and k ₀ factors for ⁷⁵Se systematic errors in Se determination in various matrices have been noticed by several users of the k ₀ method. A number of publications have been made on this subject, resulting in different k ₀ and Q ₀ values for this radio-isotope. This work consists of a re-determination of Q ₀ and k ₀ values for ⁷⁵Se using the bare and Cd-ratio methods making use of three different irradiation channels from the BR1 reactor. For this re-determination three different kinds of standards were used: a pure Se powder standard, an ICP standard solution and pure Se shots. Results were compared with previously published literary data. Differences in k ₀ with the official published data ranging from 3.5 to 12 % were observed and potential reasons for this discrepancy are discussed. A good consistency with recent work was found. The impact on recent certification and intercomparison exercises demonstrates the effectiveness of the newly proposed values.     

Measurement of k 0 values for caesium and iridium

The OPAL research reactor in Australia has been used to determine k ₀ values for ^134mCs, ¹³⁴Cs, ¹⁹²Ir and ¹⁹⁴Ir. Values for ²⁴Na have also been measured for quality control. The neutron flux at the irradiation positions was very highly thermalised (f > 2,000), resulting in almost negligible activation by epithermal neutrons. As a consequence, the contribution to the total uncertainty of the k ₀ values from epithermal-related factors such as Q ₀ and $ \bar{E}_{\text{r}} $ was very small. The measured caesium k ₀ values have been compared with the library values as well as with recent measurements by St Pierre et al. and Farina Arboccò et al. While there are k ₀ values for ¹⁹⁴Ir in the library, no ¹⁹²Ir values have been measured previously. Despite ¹⁹²Ir having a higher sensitivity than ¹⁹⁴Ir, k ₀ values were not measured during the establishment of the k ₀-method because the nuclear data available at the time indicated that the activation cross-section of ¹⁹¹Ir deviated significantly from 1/v behaviour (g(T _n ) ≠ 1), which would result in unacceptable errors if k ₀ analysis were to be carried out using the Høgdahl convention. However later nuclear data compilations showed that ¹⁹¹Ir has better 1/v behaviour than previously reported, making it suitable for k ₀ analysis using the Høgdahl convention. For completeness, k ₀ values have been determined using both the Høgdahl and modified-Westcott conventions and these have been compared with library (¹⁹⁴Ir) and calculated values.     

Neutron flux and associated k0 parameters in the RPI after the last configuration change

The Portuguese Research Reactor (RPI) is a 1 MW swimming pool type reactor, operating since the early 1960s. The fuel is MTR type, with flat plates of U-Al alloy enriched to 93% in ²³⁵U. As the core configuration changed in April 2000, it became essential to characterise the neutron field in the most useful irradiation positions of RPI, in order to guarantee the accuracy in the application of k ₀-neutron activation analysis (k ₀-NAA). Experimental values of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from the 1/E shape (a) were determined using the Cd-ratio for multi-monitor method. The neutron temperature (T _n) was obtained from co-irradiation of Lu with 1/v monitors. The results for several irradiation positions are presented and discussed in this work. Some element concentrations are determined based on the parameters obtained in this work, and compared with the certified reference material concentrations.     

Application of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA method at the HANARO research reactor

The k ₀-standardization method (k ₀-NAA) is known as one of the most remarkable progresses of the NAA with its many advantages. For the application of k ₀-NAA method at the NAA #1 irradiation position where the neutrons are well thermalized in the HANARO research reactor, KAERI, Korea, the determination of the reactor neutron spectrum parameters such as α and f have been carried out. The measured values of α and f using the “Cd-ratio” triple monitor method were 0.127±0.022 and 1010±70, respectively. To evaluate the applicability of k ₀-NAA in our analytical system, the analysis of three kinds of SRMs was executed. The analytical results showed that the relative error of most of the elements was less than 10% and the U-scores were within 2. It is turned out that the procedure of the k ₀-NAA in the HANARO research reactor is available for a practical application in the environmental fields.