The k0-method in cold-neutron prompt gamma-ray activation analysis

The k ₀-standardization method has been applied and evaluated at the cold-neutron prompt gamma-ray activation (PGA) facility of the Swiss spallation source SINQ (Paul Scherrer Institute). The k ₀-factors for 26 elements of interest were measured using chlorine as a comparator. The results showed good agreement with the values determined at other cold and thermal neutron guided beams, except for a few elements. Then, standard reference materials were analyzed to assess the accuracy of the method using the obtained k ₀-factors. Finally, the technique was used for multielement determination in various samples coming from nuclear waste storage, geochemistry and geology. In addition, the non-destructive nature of PGAA offered an interesting application in archeology.     

Development and applications of <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript> based NAA and prompt gamma-ray NAA methods at BARC

A summary of k ₀-based R&D work on neutron activation analysis (NAA), internal mono standard NAA (IM-NAA) and prompt gamma-ray NAA (PGNAA) is presented. The k ₀-based NAA was standardized by characterizing irradiation sites of research reactors, validated using reference materials and applied to samples of different origin. Recently IM-NAA method was developed, validated for small and large size samples and applied for the analysis of large size as well as non-standard geometry samples. Studies on PGNAA included characterization of neutron beam, determinations of detection efficiency and prompt k ₀-factors, and analytical applications.     

Prompt k 0-factors and relative gamma-emission intensities for the strong non-1/v absorbers 113Cd, 149Sm, 151Eu and 155,157Gd

Prompt k ₀-factors relative to chlorine and relative g-emission intensities were determined for the strong non-1/v absorbers ¹¹³Cd, ¹⁴⁹Sm, ¹⁵¹Eu,¹⁵⁵Gd and ¹⁵⁷Gd. Measurements were performed using the SNU-KAERI prompt gamma activation analysis (PGAA) facility at the Korea Atomic Energy Research Institute (KAERI). For proper experimental determination of the prompt k ₀-factors, the effective g-factor and cadmium ratio were taken into account, in consideration of the effects from the non-1/v capture cross section and neutron spectrum in the thermal and epithermal energy region. By using the actual spectrum of the neutron beam in this study, the effective g-factor was obtained by calculation, and the influence of epithermal neutrons on the capture rate was corrected by measuring the cadmium ratio for each non-1/v target isotope. The measured prompt k ₀-factors were used to check the consistency between the existing dataset of the absolute g-emission intensity and the 2200 m/s capture cross section for these isotopes.     

Correction of k<Subscript>0</Subscript>-factors for non-1/v elements based on neutron spectrum measurements

Neutron spectra were measured by the time of flight method using a rotating disk chopper system in the JRR-3M prompt gamma ray analysis system. Effective g-factors for non-1/v elements such as Cd, Sm and Gd were calculated from the measured neutron spectra and the neutron cross section data, and they was used for correcting the k ₀-factors. The resulting k ₀-factors for the cold and thermal neutron beams agreed within 10%. Furthermore, the prompt gamma ray emission probabilities of Cd, Sm and Gd were derived from the corrected k ₀-factors using other relevant physical constants.     

Standardization of NAA Using the Activation Equation and Isotope-Related Constants

A standardization method for NAA has been developed based on the activation equation and on isotope-related k _i -values that are composite nuclear constants. This approach combines the simplicity of the absolute methods with nearly the same accuracy as that obtained by the relative ones. The k _i -constants are calculated from the well measured k ₀-factors and the neutron flux is determined as with the k ₀-method. A computer program was developed for the determination of the neutron flux parameters and the concentration of the trace element. These calculations start with the measured activity of the radionuclides.     

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.     

Determination of k0- and Q0-factors of short-lived nuclides

k₀- and Q₀-factors of 18 short-lived nuclides used in reactor neutron activation analysis were determined using the Fast Irradiation and Measurement System (FIMS) of the TRIGA MARK II reactor at the Atominstitut der Österreichischen Universitäten. The Q₀-factors were either critically selected from literature, or experimentally determined according to theCd-ratio method, while the k₀-factors were additionally determined by theBare monitor method. A comparison is made with the values calculated by introduction of literature data for the input parameters. Moreover, a user oriented tabulation is presented of k₀-, Q₀-factors and related nuclear data. All results were critically tested with respect to their accuracy and precision.     

The recommended k0-factors for neutron-induced prompt gamma-ray analysis and the prompt gamma-ray emission probabilities

Recommended k ₀-factors for gamma-lines of 24 elements useful for neutron-induced prompt gamma-ray analysis (PGA) and which are not influenced by neutron spectrum differences were obtained from the k ₀-factors measured with the cold and thermal neutron guided beams of JRR-3M, by statistical calculation. The prompt gamma-ray emission probabilities were derived from the recommended k ₀-factors using atomic weight, isotopic abundance and thermal neutron capture cross section all related to the k ₀-factors, for which one can obtain accurate data. The derived gamma-ray emission probabilities for the light elements (H to Ca) agreed well within ±10% with those of the ENSDF values, which reflect recent data while the agreement for heavy elements (Ti to Pb) was ±40% with those of the ENSDF, which are still composed of old data. This revised version was published online in July 2006 with corrections to the Cover Date.     

k0-measurements and related nuclear data compilation for (n, γ) reactor neutron activation analysis

Recommended k₀-factors and related nuclear data for use in (n, γ) activation analysis are given for 72 isotopes. In addition the basic nuclear constants and experimental parameters needed in the k₀ standardization method are reviewed. For convenient data reduction, computer programs were developed.     

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.     

Determination of <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-values for some elements in neutron capture gamma-ray for prompt gamma activation analysis

Exploration and modification of data for k ₀-PGAA (prompt γ-ray activation analysis) values used as standards for k ₀ standardization are needed. An integrated system has been installed and calibrated in Hot Laboratories Center for PGAA, using ²⁵²Cf isotopic neutron source with neutron flux of 6.16E8 n/cm² s. The prompt k ₀-factors of about 12 elements were determined versus the 1951.1 keV γ-ray of the ³⁵Cl, as well as analyzing crude oil and oil product samples. The concentrations of the elements in crude oil H, B, Mg, Al, Na, Si, P, S, Cl, V and Cd were 1.18E5, 0.084, 5.48E2, 8.45E2 4.88E2, 1.62E2, 3.72E2, 8.2, 144.3, 393 and 209.2 ppm while in oil product samples were 1.32E5, 5.87, 4.56E2, 4.22E2, 7.16E3, 699, 157, 8.74, 492.3, 61 and 198.2 ppm. Validation of the k ₀-PGAA was applied in analyzing standard IAEA reference material (soil-7) which give good agreement with the literature data. The ²⁵²Cf neutron beam in radiation position was characterized by the cadmium-ratio method, and found that the cadmium ratio (f), was 160.     

k0-Measurements and related nuclear data compilation for (n, γ) reactor neutron activation analysis

The determination of k₀-factors has been continued covering now the relevant gamma-lines of 112 analytically interesting radionuclides. Experimental details are given, and an extended tabulation is presented of complex activation decay types and the associated expression for the parameters involved in the k₀-method.Deceased May 1988.     

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.     

Measurement of k0-Factors in Prompt Gamma-Ray Neutron Activation Analysis

The guided thermal neutron beam at 100 MW Dhruva research reactor facility of Bhabha Atomic Research Centre (BARC) was used to carry out prompt gamma-ray neutron activation analysis (PGNAA). The prompt k ₀-factors have been determined for the isotopes of the elements H, B, K, Co, Cu, Ca, Ti, Cr, Cd, Ba, Hg and Gd with respect to 1951 keV gamma-line of ³⁶Cl. The prompt k ₀-factors for H, Cl and Cu were also measured with respect to the 1381 keV gamma-line of ⁴⁹Ti. Different samples like NH₄Cl, Ti metal, cobalt chloride and other stoichiometric compounds and pure metals were used for this purpose. Prompt gamma-rays were accumulated using a 22% HPGe detector connected to a PC based 8k MCA in single mode counting. The energy calibration in the range of 100–8500 keV was carried out using gamma-rays from ¹⁵²Eu and ⁶⁰Co, and the prompt gamma-rays from ³⁶Cl whereas the absolute detection efficiency for this energy range was determined using ¹⁵²Eu and prompt gamma-rays from ³⁶Cl and ⁴⁹Ti.     

Rate constants of reactions of chlorine atoms with aliphatic hydrocarbons and halogen derivatives in the liquid phase

The kinetics of liquid phase chlorination of methane in a difluorodichloromethane medium has been studied in a temperature interval of 293–150 K. The value of activation energy found for the hydrogen abstraction stage by a chlorine atom (E₁) equals 14.2 ± 2.5 kJ/mol, with the processes of chlorine atoms recombination and the cage effect being taken into account. The method of competitive reactions has been employed to assess the constants of reaction of chlorine atoms (k₁) with ethane, propane, hexane, ethylene, allyl bromide, allyl chloride, ethyl chloride, and cyclohexane in nonpolar solvents, viz. difluorodichloromethane and 1,2-dibromotetrafluoroethane. The values (k₁) obtained in the liquid phaseare two to four orders lower than those in the gas phase, while the activation energy is 2–6 kJ/mol higher.     

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.     

Application of the INAA methods for KRISS infant formula CRM analysis: standardization of INAA at KRISS

We have established an instrumental neutron activation analysis (INAA) method, including k₀-based INAA, at the Korea Research Institute of Standards and Science (KRISS) for the certification of reference materials. As part of establishing INAA measurements, KRISS infant formula certified reference material was analysed for multiple elements at three different metrological institutes: KRISS and NIST for the standard comparator method, and JSI for the k₀-INAA method. The mass fraction of most elements was consistent within expanded uncertainty (k?=?2). In addition, the results were used to verify the validity of elemental analysis of Zn using the standard comparator INAA at KRISS, and spreadsheet-based INAA calculations were evaluated.

     

Development and implementation of thek 0-standardization and other parametric methods of INAA in Cuba. Part II

The main results obtained during the characterization of the Triga Mark III reactor at NNRI, Salazar, Mexico, the development of the nonconventional multimonitor HAV-1, the use of Certified Reference Material (CRM) as multimonitor fork ₀-factors experimental determination, and to study the reactor power and slowing-down thickness dependencies of the reactor flux parameters and its influence ink ₀-INAA are presented. The experience of thek ₀-INAA group at ISCTN, in the application of this analytical technique for different purposes is resumed.     

The use of ko-factors as a tool for a critical evaluation of reactor thermal and epithermal (n, γ) cross-sections and of absolute gamma-intensities

By comparison of experimental k₀-factors, determined in reactor positions with greatly different thermal-to-epithermal neutron flux ratios, and by comparison of experimentally determined and theoretically calculated k₀-factors, it is possible in some cases to select best values from literature data for (n, γ) activation cross-sections and for absolute gamma intensities. This is demonstrated for⁹⁷Zr,⁹⁵Zr,⁵⁶Mn and⁶⁵Zn.     

Neutron spectrum correction of k0-factors for k0-based neutron-induced prompt gamma-ray analysis

Neutron spectrum correction has been attempted for the k₀-factors of the non-1/v elements which are affected neutron spectrum difference. Effective g-factors and Westcott g-factors, which are neutron spectrum correction factors obtained from an actual neutron spectrum and the Maxwellian distribution, respectively, for the non-1/v elements were calculated using their neutron cross section data of JENDEL-3.2. The neutron spectrum correction was made for the measured k₀-factors of the non-1/v elements such as Cd, Sm and Gd with the cold and thermal guided neutron beams of JRR-3M using the g-factors. The corrected k₀-factors between the cold and thermal neutron beams using both g-factors for both neutron beams agreed well for Cd. However, 9 to 44% deviations have been found for Sm and Gd, respectively.