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.     

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.     

Applications of k 0 NAA at FRM II with high f values

The research reactor FRM II offers different irradiation facilities with highly thermalized neutron flux. 3 facilities for the k ₀ neutron activation analysis (k ₀ NAA) will be introduced shortly. The influence of flux parameter α on the concentration calculation of samples irradiated in a neutron field with very high ratio of thermal to epi-thermal neutron flux f > 1,000 are here investigated. Even for the most k ₀ isotopes with big Q ₀ values, the uncertainty of a concentration calculation without α correction is <3 %, when the f value larger than 3,000. The uncertainty is about 5 % for the isotope ⁹⁶Zr in this case. The k ₀ library of the computer program MULTINAA is updated. A standard reference material IAEA/soil-7 was analyzed to verify the k ₀ NAA at FRM II.     

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.     

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.     

Determination and evaluation of fission k0-factors for correctionof the 235U(n,f) interference in k0-NAA

In order to provide a tailored solution for the correction of the ²³⁵U interference in k₀-NAA, fission k₀-factors for the analytically relevant radionuclides/gamma-lines (versus gold as the comparator), are experimentally determined in four channels of the Gent THETIS reactor. A comparison is made with former data from the literature. The new evaluated results are to be implemented in the forthcoming upgrade of the DSMKayzero software package for k₀-NAA.     

Recalibration of the irradiation facilities in the Thetis reactor, with an examination of the a versus E behavior in the keV neutron energy range

The reloading of research reactor Thetis (INW, Gent), in April 1996, involved the re-calibration of the irradiation facilities used for k ₀-NAA. In some channels, the values of the re-measured parameters f and a significantly deviated from the ones before reloading, and the effect of this on the concentration results is demonstrated. Some additional experimental work was done in two irradiation facilities, one well-thermalized and another with a hard neutron spectrum, in order to examine the behavior of a with neutron energies up to about 60 keV. This study was performed in the context of a lasting controversy regarding the accuracy of the k ₀ and Q ₀ values for the ^95,97Zr-isotopes, especially in view of the high ⁹⁴Zr(n,g) effective resonance energy. In the irradiation channels under consideration, no evidence was found of a versus energy dependence     

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.     

The use of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-IAEA program in NIRR-1 NAA laboratory

The k ₀-IAEA program developed for implementation of the single comparator instrumental neutron activation analysis method (k ₀-INAA) has been used for elemental analysis with NIRR-1 irradiation and counting facilities. The existing experimental protocols for routine analysis based on the relative method were used to test the capability and reliability of the program for the analyses of geological and biological samples. The Synthetic Multi-element Standards (SMELS) types I, II and III recommended by the international k ₀ user community for the validation of k ₀-NAA method in NAA laboratories, furthermore, the following standard reference materials: NIST-1633b (Coal Fly Ash) and IAEA-336 (Lichen) were analyzed. Results obtained with the version 3.12 of the k ₀-IAEA program were found to be in good agreement with the data obtained with the established relative method using WINSPAN-2004 software. Detection limits for elemental analysis of geological and biological samples with NIRR-1 facilities are provided.     

Experimental and MCNP calculations of neutron flux parameters in irradiation channel at Es-Salam reactor

The Algerian research reactor (Es-Salam) is a 15 MW heavy water reactor type, operating since 1992. It became essential to characterize the neutron field in the most useful irradiation positions, in order to guarantee the accuracy in the application of k ₀-neutron activation analysis (k ₀-NAA). Experimental value of the thermal to epithermal neutron flux ratio (f) and of the deviation of the epithermal neutron spectrum from 1/E shape (α) were determined using different methods. This work focuses the verification of Monte Carlo neutron flux calculation in typical irradiation channel. Comparison of the results for parameter f obtained experimentally and by Monte Carlo simulations shows good agreement in the irradiation channel studied. The difference between both results is about 2.08%.     

Neutron spectrum parameters in irradiation channels of the Nigeria Research Reactor-1 (NIRR-1) for the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA standardization

Summary The first nuclear research reactor in Nigeria has been commissioned for neutron activation analysis and limited radioisotope production. In order to extend its utilization to include the k₀-standardization method, the following neutron spectrum parameters in inner and outer irradiation channels were determined by the “Cd-ratio for multi-monitor method”: the thermal-to-epithermal flux ratio, f, and the epithermal flux shape factor, α. Neutron spectrum parameters determined in the inner irradiation channel B2, are: α = -0.052±0.002 and f = 19.2±0.5. For the outer irradiation channel B4, the neutron spectrum parameters were found to be α = +0.029±0.003 and f = 48.3±3.3. The results are compared with the neutron spectrum parameters of other reactor facilities with similar core configuration such as the Slowpoke and Miniature Neutron Source Reactor facilities available in the literature.     

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.     

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.     

Trace and essential elements determination in baby formulas milk by INAA and k 0-INAA techniques

As a part of the food analysis program executed at Es-Salam research reactor by neutron activation analysis laboratory, the concentration of As, Ba, Br, Ca, Fe, K, La, Rb and Zn in baby formulas milk have been determined by using INAA and k ₀-NAA techniques. It was found that the concentration of all elements obtained by both techniques was relatively identical for the three brands of the 0–6 and 6–12 months of analyzed samples. In addition, the analytical results have been compared with those given by producers.     

Using synthetic multi-element standards (SMELS) for calibration and quality control of the irradiation facilities in the BR1 reactor

The thermal to epithermal neutron flux ratio (f) and the deviation of the epithermal neutron spectrum from the 1/E shape (α) are essential parameters for the correct application of k ₀-standardized neutron activation analysis. Several methods are applied for the determination of f and α. They are based on Cd-covered multi-monitor or on bare-irradiations methods. The recently developed and characterized synthetic multi-element standards (SMELS) were designed as a validation tool for the proper implementation of the k ₀-NAA method in a laboratory. In particular, SMELS Type III contains Au and Zr, thus allowing the direct determination of f and α. It could, therefore, replace the traditional flux monitors. Furthermore, it could be used as a quality control material to monitor the stability of the irradiation facility and the detector. This paper presents the accuracy of the f and α determination and the feasibility of quality control using SMELS for irradiation channel Y4 of the BR1 reactor.     

Instrumental neutron activation analysis of Moroccan geological samples using the k0-standardization method

Instrumental neutron activation analysis (INAA) for traces and major elements of several geological samples from “Zgounder” region in Morocco was performed utilizing the k ₀-standardization method. Sample irradiation has been done by the 250 kW Triga Mark II reactor at Jozef Stefan Institute in Slovenia. Due to its accuracy, sensitivity and specificity, the k ₀-standardization method is the most suitable method for non-destructive multielement analysis mainly for trace elements in rocks. It requires an accurate knowledge of the parameters of the irradiation facilities and other instrumentation parameters. It is an absolute standardization method, where the absolute nuclear data are replaced by a nuclear constant, the k ₀-factor, determined experimentally with high accuracy. More than 40 elements were determined using about 30-second short and about 7-hour long irradiations. Gamma-rays emitted from the irradiated samples have been determined by a high purity germanium detector. Accuracy was assessed using the standard reference material AGV-1. This was less than 1% for major elements and about 5% for traces. This revised version was published online in July 2006 with corrections to the Cover Date.     

Determination of k 0-factors and validation of k 0-INAA for short-lived nuclides

For standardization of k ₀-based instrumental neutron activation analysis, k ₀-factors for short-lived nuclides (half-lives—11 s to 37 min) of elements F, Se, Sc, Al, V, Ti, Cu, Ca, Mg, I, and Cl with respect to gold (¹⁹⁷Au) were determined using pneumatic carrier facility (PCF) at CIRUS reactor of BARC, Mumbai. Characterization of PCF was carried out by cadmium-ratio method using Au and Zr. The experimental k ₀-factors of the isotopes were found to be in good agreement with the recommended k ₀-factors in most of the cases, as evident from the values of % error and U-score at 95% confidence level. The method was validated by determining concentrations of elements through their short-lived nuclides in one type of the synthetic multielement standards (SMELS-I) obtained from SCK-CEN, Belgium. The method was also applied for determination of concentrations of some of the elements in two reference materials of IAEA, SL-3, and SL-1.     

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.     

Implementation of <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-standardization method of the INAA at ETRR-2 research reactor

The k ₀-method of INAA standardization has been implemented using the irradiation facilities of the fast pneumatic rabbit and some selected manually loaded irradiation positions, which designated for short and long irradiation, respectively, at Egypt second research reactor. The neutron flux parameters (f and α) in each site have been determined using Zr–Au sets as neutron flux monitors. The reference materials coal NIST 1632c and IAEA-Soil 7 were analyzed for data validation and good agreement between the experimental values and the certified values was obtained.