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.     

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.     

IRMM-3100a: A new certified isotopic reference material with equal abundances of 233U, 235U, 236U and 238U

The new so-called Quad-IRM (“Quadruple Isotope Reference Material”) was prepared from highly enriched ²³³U, ²³⁵U, ²³⁶U and ²³⁸U isotopic materials using an optimized combination of gravimetrical mixing and mass spectrometry. Within the mixing process the isotope ratios were adjusted to about n(²³³U)/n(²³⁵U)/n(²³⁶U)/n(²³⁸U) = 1/1/1/1 and certified with expanded relative uncertainties of 0.0054% per mass unit (coverage factor k = 2). This new isotope reference material is ideal for verifying the inter-calibration of multi-detector systems in isotope mass spectrometry.The certified n(²³³U)/n(²³⁶U) ratio of IRMM-3100a was derived from the mass metrology data of the gravimetrical mixing of highly enriched ²³³U and ²³⁶U materials. It was verified by thermal ionization mass spectrometry (TIMS) measurements using the classical total evaporation (TE) and modified total evaporation (MTE) methods. The n(²³⁴U)/n(²³⁶U), n(²³⁵U)/n(²³⁶U) and n(²³⁸U)/n(²³⁶U) ratios were then determined by TIMS using the n(²³³U)/n(²³⁶U) ratio for internal normalization and using a multi-dynamic measurement procedure in order to circumvent any possible influence and uncertainties from Faraday cup efficiencies and amplifier gain factors. The certified n(²³⁵U)/n(²³⁶U) and n(²³⁸U)/n(²³⁶U) ratios were additionally verified using the classical and modified total evaporation methods using two TIMS instruments at IRMM and one TIMS instrument at IAEA-SGAS. The verification data can be regarded as results obtained at three independent instruments at two different nuclear safeguards laboratories.     

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.     

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.     

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.     

A simplified method to replace the Westcott formalism in k 0-NAA using non-1/v nuclides

The Westcott formalism was developed to accurately describe the activation of nuclides whose neutron capture cross-sections do not follow the 1/v-law and it was incorporated in the k ₀-method about 20 years ago. However, its implementation in the original fashion is not easy, requiring the use of a different formalism for the non-1/v nuclides, with a g(T _n) factor for the thermal neutron activation and an s ₀ factor for epithermal activation, the measurement of the neutron spectral index of the irradiation channel and the irradiation of a temperature monitor with each batch of samples as well. In this work we investigated the accuracy of maintaining the simpler formula of the Høgdahl convention for all nuclides and introducing the g(T _n) factor for the thermal neutron activation for non-1/v nuclides. The epithermal activation is calculated using a Q ₀-value estimated from the measured s ₀-value for non-1/v nuclides. This new approach has been shown, by calculations with the parameters of the neutron spectra of five irradiation channels, not to give a significant loss of accuracy relative to the Westcott formalism.     

In-beam determination of k0 factors for short-lived nuclides

The prompt -activation analysis (PGAA) facility at Budapest Research Reactor offers a unique possibility to perform in-beam measurements. Several k ₀ factors for decay -lines of short-lived nuclides have been determined accurately by means of in-beam activation. The present values compare well with literature data. New k ₀ factors are proposed for ^24mNa and ^60mCo.     

Experimental determination of k 0, Q 0 factors,effective resonance energies and neutron cross-sections for 37 isotopes of interest in NAA

The recommended k ₀ nuclear data from 2003 has been re-investigated by some authors during the last decade, motivated by some discrepancies that were systematically observed during the analysis of reference materials. Their significant findings have not been included (yet) on a newer compilation, as it is difficult to draw conclusions on the accuracy of k ₀ and Q ₀ factors when the statistical population of independent experimental values are quite scarce. In some cases, a strong correlation to the adopted Q ₀ factor means that a direct comparison between the results of different authors is not possible if the data required for a proper renormalization was not provided. At the SCK-CEN and UGent (Belgium) we would like to continue with the experimental k ₀ determination exercises performed during the last years and to supply to the k ₀-community with the nuclear data of 37 additional target isotopes, for a total of 77 isotopes investigated since 2012. The isotopes were investigated on up to 4 channels of the BR1 reactor at the SCK-CEN, obtaining values with <2.6 % uncertainty. Our results are discussed and compared to the literature elsewhere.     

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.     

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).     

Correction for neutron induced reaction interferences in the NAA k0-standardization method

A study is made of the correction, in k₀-standardized NAA, for interferences caused by fast neutron induced threshold reactions, second order reactions and²³⁵U-fission. The following examples are elaborated: determination of the Cr and Sc concentrations in a reference human serum, corrected for the⁵⁴Fe(n,)⁵¹Cr and⁴⁴Ca(n,;^–; n,)⁴⁶Sc interferences, respectively, and the determination of Zr, Cs, La, Ce, Nd and Sm concentrations in USGS BCR-1 and G-2, corrected for²³⁵U(n, f) interference. A detailed uncertainty analysis and a comparison of the analytical results thus obtained with other literature values proves that the interferences can be accurately corrected for by employing the usual neutron flux monitors in the k₀-method, namely a Zr-foil and a dilute Au–Al alloyed wire.     

Experimental determination of k 0 nuclear data for the cesium radionuclides

The current (official) k ₀ nuclear data for the cesium radionuclides was determined circa 1987 and was partially adopted from older literature. In this work we aimed at the redetermination of experimental k ₀, Q ₀ and $\bar{E}$ _r factors with metrological care. The results are in good agreement with more recent results from other authors. Our Q ₀ and $\bar{E}$ _r values were 2–15 and 25 % different, respectively. The k ₀ factors were determined according to the cadmium subtraction technique, resulting in values 3–7 % different than the official ones. Our precision and accuracy is discussed.     

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 2012 recommended k 0 database

Many overview papers have been published with recommended nuclear data for use in the k ₀ method of NAA and made available in scientific journals or in the form of a downloadable database. In September 2009, the k ₀-International Scientific Committee formed the k ₀-Nuclear Data Committee (k ₀-NDC) whose first task was to collect all these data at a single place to facilitate updating and to correct any evident errors. This task of the k ₀-NDC was successfully completed in March 2012 when the 2012 recommended k ₀ database was published in the form of an Excel file.     

k 0-RNAA used in determination of 129I in a mixed resin sample

A k ₀-RNAA procedure was developed to determine ¹²⁹I in a mixed resin sample. CH₄ extraction and (NH₄)₂SO₃ back-extraction were used to separate ¹²⁹I in ashed samples. The ¹²⁹I target sample for irradiation in the reactor was prepared by heating the (NH₄)₂SO₃ back-extraction solution to reduce its volume and then to dry it in a quartz ampoule. No MgO and LiOH were needed during the target sample preparation. After irradiation, the nuclide ¹³⁰I was purified by combining hydrated antimony pentoxide column and CH₄ extraction separations. A k-factor was determined for the reaction of ¹²⁷I (n, 2n) ¹²⁶I and used for iodine chemical yield determination. The apparent ¹²⁹I concentrations of five nuclear reaction interferences were calculated. The relative standard deviation of three ¹²⁹I determinations was found to be 3.5 %. The ¹²⁹I content in the analyzed resin was found to be 1.36 × 10^?9 g/g (8.63 × 10^?3 Bq/g) with a relative uncertainty of 9.1 %. The detection limit of ¹²⁹I was calculated to be 7.4 × 10^?13 g (4.7 × 10^?6 Bq) in a k ₀-RNAA of a blank sample.     

Experimental determination of k 0 , Q 0 , \bar{E}_{r} factors and neutron cross-sections for 41 isotopes of interest in Neutron Activation Analysis

The k ₀ -literature has been reviewed every decade but some of its nuclear data is still more than 30 years old. Sometimes Q ₀ values were adopted from the nuclear data at that time or were experimentally determined by only 1 laboratory. Other isotopes were listed with accurate pairs of (k ₀ , Q ₀ ) values but were also quoted as candidates for redetermination for different reasons (i.e. imprecise cadmium transmission factors, half-lives). In this work we aim at the experimental re-determination of k ₀ and Q ₀ values for 41 isotopes of analytical interest while introducing a methodology for simultaneous $ \bar{E}_{r} $ and Q ₀ determination employing N irradiation channels. In order to satisfy the metrological level required, up to 12 repeats per standard were irradiated in up to 4 irradiation channels of the Belgian Reactor 1 (BR1, SCK?CEN) having a wide spread in neutron characteristics. Our relative percentile differences to the literature values were usually ≤10 % for Q ₀ factors, ≥25 % for $ \bar{E}_{r} $ values and ≤4 % for k ₀ values. Our precision and accuracy are discussed thoroughly.     

A performance comparison of k<Subscript>0</Subscript>-based ENAA and NAA in the (K,Th, U) radiation dose rate assessment for the luminescence dating of sediments

Summary Recently, in our laboratory an intercomparison was made of methods for the annual radiation dose determination (assessed from direct radiation counting and/or from the measurement of the K, Th and U contents) applied to luminescence dating of loess and sand sediment, whereby the emphasis was put on their precision and accuracy. Although these properties are important, the duration of the measurement is also a practically relevant aspect. Indeed, direct alpha, beta and gamma-counting can last a week or more, and the determination of K, Th and U via NAA can take up to three weeks to enable proper gamma-ray spectrometry of the long-lived ²³³ Th/²³³Pa. Therefore, in the present work the performance of k₀-based epiCd-NAA (ENAA, with irradiation under a cadmium cover) when applied to sediments is compared to k₀-NAA. As concluded, with the use of k₀-ENAA the analysis turnaround time could be considerably reduced from ~3 weeks to ~ 2.5days, while maintaining satisfactory accuracy, precision and determination sensitivity.     

Role of interlayer M k atoms and H2O molecules in the structure formation of M k (VUO6) k · nH2O uranovanadates

M ^k (VUO₆) _k · nH₂O uranovanadates of alkali (Li, Na, K, Rb, Cs), alkaline-earth (Mg, Ca, Sr, Ba), 3d transition (Mn, Fe, Co, Ni, Cu, Zn), and rare-earth (Y, La, Ln) elements were prepared by precipitation from solutions under hydrothermal conditions and in solid-phase reactions. The composition and structure of these compounds and the role of M ^k atoms and H₂O molecules in the formation of their structure were studied by X-ray diffraction, IR-spectroscopy, thermal analysis, and chemical analysis.     

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.