New technique for the determination of trace elements using multiparameter coincidence spectrometry

Multiparameter coincidence g-ray spectrometry based on g-g coincidence is widely used in the field of nuclear structure studies, and has produced many succesful results. In this paper, feasibility of the method for neutron activation analysis of trace elements was studied. Particularly, a long-lived radioisotope ¹²⁹I (T_1/2 = 1.57^.10⁷ y) in algae samples and iridium in geological samples has been determined.     

Multi-element analysis of biological samples after intense neutron irradiation an fast chemical separation

For the simultaneous determination of many elements in small biological samples, a multi-element analysis has been developed using neutron activation. After a 24-hr irradiation in a neutron flux of 2.5·10¹⁴ n·cm⁻²·sec⁻¹ and after immediate chemical separation without cooling, it was possible to analyse 24 elements in bovine liver (NBS-SRM 1577). The separation apparatus, set up in a shielded cell can work four samples simultaneously, and its operation is fast enough to allow the detection of radioisotopes with a half-life of about 2 hrs (¹⁶⁵Dy,^57mSr,⁵⁶Mn). Amounts lower than 10⁻³ μg of Dy, Eu, Pr, Sm and Yb were determined.     

Preconcentration neutron activation analysis of trace elements in surface waters by coprecipitation with pyrrolidinedithiocarbamate in the presence of Bi(III)

A simple preconcentration method is described for the simultaneous coprecipitation of Cd(II), Co(II), Cu(II), Mo(VI), U(VI), V(V) and Zn(II) from surface water samples followed by quantitation using neutron activation analysis. Ammonium pyrrolidinedithiocarbanate (APDC), anthranilic acid and 8-hydroxyquinoline have been investigated as possible coprecipitating agents. The suitability of Bi³⁺, Fe³⁺, Ni²⁺ and Pb²⁺ ions as metal carriers has also been studied. It has been found that the above elements can be quantitatively coprecipitated with APDC in the presence of Bi³⁺ carrier at pH 4. The precision and accuracy of the method for all elements are found to be between ±2 and 10%. The enrichment factors are of the order of 10³. The detection limits are in the ppb range varying between 0.04 ng · ml^–1 for Co and V and 5 ng · ml^–1 for Zn. The method has been applied to tap and well waters, and river and lake water samples collected from Halifax County, Nova Scotia.     

Determination of 17 trace elements in gallium arsenide by reactor neutron activation analysis

A method has been developed for the simultaneous determination of 17 trace elements in gallium arsenide. The method involves reactor neutron irradiation of the samples, distillation of the arsenic matrix activity and Ge(Li) γ-ray spectrometry. For a sample size of 0.1 g and a 10-day irradiation at 2·10¹³ n cm^-2 s^-1, the detection limits vary from 70 p.p.b. (tin) down to 5·10^-3 p.p.b. (scandium).     

Determination of 22 elements in geological samples by instrumental neutron activation analysis

An instrumental neutron activation analysis (INAA) method has been developed for multi-element determination in geological samples. The INAA method consists of irradiation of samples for 90 sec at a flux of 1.0·10¹² n·cm⁻²·sec⁻¹ and determination of 12 elements by using their short-lived nuclides. Samples have been re-irradiated for 3 hrs for measuring concentrations of another 10 elements. Precision and accuracy of the INAA method have been evaluated by analysing samples and USGS standard reference materials. Precision and accuracy are within±15% and ±10%, respectively.     

Instrumental neutron activation analysis of monomineral fractions of sulfide minerals and quartzes

A method has been worked out of multi-elemental instrumental neutron-activation analysis INAA of small weights some mg of monomineral fractions of sulfide minerals pyrites, galenites, chalcopyrites, arsenopyrites, bornites, chalcosines and quartzes. The samples were irradiated in a nuclear reactor under a flux of 1.3·10¹³ n·cm⁻²·s⁻¹. For measuring the gamma radiation of the exposed samples Ge(Li) gamma-spectrometers with semiconductor detectors were used. Determined in sulfide monofractions were the elements: Co, Sc, Ag, Se, Sb, Cr, Fe, Zr; rare-earth elements: Ce, Sm, Eu and others at content levels of 10⁻¹−10⁻⁴%. In quartzes they were: Mn, Na, Sb, Cr, Sc, Fe, Co at content levels of 10⁻⁵−10⁻⁷% and Au to n×10⁻⁹%. A special method has been worked out for the determination of In in sulfides with the irradiation of samples in a cadmium screen. An example is cited of using the method for studying some peculiar features of the genetics of copper pyrite deposits. The data on the distribution of admixture elements in sulfide monofractions produced in this work made it possible to conclude that the oreformation in the deposits has a stage-by-stage character.     

Improved detection sensitivity of elements in solids via laser postionization in laser desorption time‐of‐flight mass spectrometry

A newly constructed laser desorption (532 nm, 5 ns) and laser postionization (266 nm, 5 ns) time‐of‐flight mass spectrometer (LD‐LPI‐TOFMS) has been applied for improving the detection sensitivity of elements in solid samples. This method affords to acquire the information of the elemental impurities in solid standards as well as limit of detection (LOD) down to 10⁻⁸ g/g for some elements. Neutral atoms of solids are generated by low‐irradiance laser desorption (< 10⁸ W/cm²), followed by high‐irradiance laser postionization (~ 10⁹ W/cm²) of the desorbed atoms, facilitating to decouple the desorption and ionization processes in spatial and temporal domain. This non‐interacting feature overcomes the discrimination between deteriorating spectral resolution at high irradiance (10⁹–10¹¹ W/cm²) and limited detectable elemental species and high LOD at low or medium irradiance (below 10⁹ W/cm²). The utilization of originally “wasted” neutral atoms by laser postionization will help improve atom utilization and instrumental sensitivity. In this work, getting the utmost out of the consumed neutral atoms instead of an increment in sampling amounts is given attention with high priority for achieving high sensitivity and low LOD, which is especially useful on the occasions where very low sample consumption is desired.     

Interferences of oxide, hydroxide and chloride analyte species in the determination of rare earth elements in geological samples by inductively coupled plasma-mass spectrometry

The analytical procedure for the determination of Ba and rare earth elements in rocks and minerals by ICP-MS is described. The yield of mono-oxide and hydroxide ions of Ba and rare earth elements, and chloride ions of Ba has been determined. A Microsoft Excel spreadsheet template has been written to calculate the expected peak intensities for all possible analyte species (M⁺, MO⁺, MOH⁺ and MCl⁺) as a function of the mass number. The degree of interferences of different analyte isotopes is estimated and interferent equivalent concentrations are given for elements, for which no isotope free from interferences is available. The method is applied to the analysis of the four Geo-Reference samples AC-E, GSP-1, G-2 and AGV-1; the analytical accuracy is better than ±10% for most of the elements when compared with recommended reference values.     

Trace determination of beryllium by heavy ion activation analysis

A novel procedure for measuring the concentration of trace beryllium in different samples has been studied using¹¹B heavy ion activation analysis. The specific reaction,⁹Be/¹¹B, 2n/¹⁸F, is sensitive and selective when using a 10 MeV¹¹Be³⁺ bombardment energy. The detection limit for a nondestructive analysis is 0.1 ng for a 2 h irradiation in a A cm^–2 beam current. A precision of 12% was achieved at the 50 g g^–1 level. Beryllium has been determined in a standard beryllium-copper alloy NBS-SRM C1123. Glass samples containing up to 61 trace elements were also analyzed nondestructively. When using a clean vacuum irradiation chamber, the technique might allow ultra-trace determinations, dealing with solid samples of a few milligrams.     

Elemental analysis of the Taiwanese health food Angelica keiskei by INAA

The health food Angelica keiskei, planted and consumed as an oriental herb, was sampled from five farms in Taiwan. The determination of minor and trace elements identified in the roots, fresh leaves and stems of the plant, as well as in end-products such as tea bags and capsules, is essential for estimating the recommended daily intake for ensuring optimum health safety. Samples were homogenized prior to freeze-drying, and were irradiated with a neutron flux at about 2.0^.10¹² n^.cm^-1.s^-1. A total of 17 elements were analyzed using INAA. In the collected samples the elements exist in widely differing concentrations, ranging from 10⁵ to 10^-2 mg/g for different farms. We found that aluminum is more highly concentrated in roots than in any other part of the plant. Selenium was the only element analyzed down to 10^-1 mg/g in the leaves. Meanwhile, arsenic was also found in the roots and stems at levels of nearly 10^-2 mg/g. The elemental concentrations and maximum daily intake (MDI) of this herb are compared with those of Angelica sinensis (Danggui in Mandarin), Ligusticum chuanxiony (Chuanxiong in Mandarin) and Panax ginseng (Ginseng in Mandarin) as well as with the recommended daily dietary intake values for Taiwanese consumers, developed by the WHO.     

Study of the correlation of trace elments in human hair and internal organs by NAA

24 male autopsy cases aged 35–60 years have been collected from Shanghai China to study the relationships between human hair and internal tissues. Autopsy samples of hair, kidney-cortex, liver and lung were analyzed. A radiochemical neutron activation analysis (RNAA) based on a simple group extraction scheme was used for measuring the trace elements As, Cd, Hg, Cu and Zn. Zinc diethyldithiocarbamate Zn(DDC)₂ and methly isobutyl ketone-iodide have been chosen as reagent. Trace element of Se was determined by instrumental neutron activation analysis (INAA). A SLOWPOKE reactor with a thermal neutron flux of 8·10¹¹ n·cm^–2·s^–1 and a swimming pool type reactor with a thermal neutron flux of 1·10¹³ n·cm^–2·s^–1 were used for short and long irradiation of samples, respectively. The reliability of methods has been checked by analyzing biological standard reference materials Horse Kidney (IAEA H8), Tomato Leaves (NBS 1573) and Human Hair (NIES-5). The analytical results show that toxic elements As, Cd and Hg exist in a larger individual variability than the essential elements of Cu, Se and Zn for each tissue. A linear regression analysis related to the six elements of primary interest for the IAEA Coordinated Research Program (CRP) has been done by a computer program for each pair of hair-tissue. A positive correlation is found between concentration of As in hair and kidney-cortex, the correlation coefficient r is 0.751 (p<0.01). Positive correlations between concentration of Se in hair and liver, kidney-cortex and lung are also observed in this study. It shows that the elements As and Se in hair may be useful indicators for assessing certain internal tissues of normal persons. A comparison of Cd concentration in lung shows a significant difference between smokers and non-smokers. A significant correlation between element Cd and Zn in kidney-cortex is also presented in this paper.     

Polyatomic ions in thermal ionisation mass spectrometry — challenges and opportunities

Polyatomic ions, often considered as causing interference in ICP-MS, SSMS and GDMS, are useful in thermal ionisation mass spectrometry (TIMS) for determining the atomic ratios of the elements, particularly for light elements. The objective of this paper is to provide a detailed discussion on the handling of the isotopic measurement data in TIMS using polyatomic ions, a useful technique for light elements, to reduce isotope fractionation effects. Taking as an example the Li₂BO₂⁺ ion for the determination of the ⁶Li/⁷Li or ¹⁰B/¹¹B ratio of the unknown sample, a detailed theoretical analysis is presented for optimum selection of the pair of polyatomic ions to be used to determine the isotopic ratio of the element. The theory is supported by experimental data from the literature in three different examples: (i) the isotopic analysis of natural Li samples using the SRM-951-B isotopic standard; (ii) the isotopic analysis of an enriched ⁶Li sample using SRM-951-B; (iii) the isotopic analysis of an enriched ¹⁰B sample using natural Li (Svec standard). It is shown that the four polyatomic peaks observed in the m/z range of 54–57 are of practical importance. A qualitative idea can be obtained about the isotopic composition of Li and B in the sample (natural or enriched) based on the intensity distribution of these four peaks in the mass spectrum. When calculating accurate atomic ratios from the observed intensities of the polyatomic peaks, a simple “rule of thumb” should be kept in mind: the polyatomic ratio that is closer to the expected atomic ratio provides an accurate value of the atomic ratio of the element in the unknown sample. Even between the two polyatomic ion ratios, better accuracy is possible in cases which do not magnify the error during calculation and show less isotopic fractionation in the ion source. It has been stressed that the two peaks of highest intensity in the polyatomic ion are not necessarily the best for arriving at atomic ratios during the analyses of unknown samples, for depleted as well as enriched ⁶Li and ¹⁰B samples.     

Instrumental neutron activation analysis of geochemical and cosmochemical samples: A fast and reliable method for small sample analysis

We have developed a fast and reliable procedure to routinely measure the abundances of up to about 35 elements even in small (<1 mg) samples. Depending on the type of samples, they are either irradiated for about 8 hours at a flux of about 2·10¹²n·cm^–2·s^–1, or up to 100 hours at a flux of about 6·10¹³n·cm^–2·s^–1. As standards, high-purity synthetic multielement standards and well-characterized geological reference materials are used. Synthetic standards are used as primary standards because they have several advantages over secondary (geological) standards. Three to four counts are done one each sample, starting 1–3 days after the end of the irradiation. We use high-purity germanium (HpGe) detectors with high efficiencies and very good energy resolution (1.6–1.8 keV at 1332 keV). To allow high throughput rates we use fast preamplifiers and gated integrator spectroscopy amplifiers with fast fixed conversion time ADCs. The signals are fed into an acquisition interface module (AIM) and via Ethernet into a Micro VAX. To allow better peak deconvolution, 8k spectra are taken where possible. A specially designed annular NaI(TI) guard detector allows Compton suppression spectrometry. The system uses standard software and was tested with sets of geological standards and has given reliable results for a wide variety of samples, e.g., cosmic spherules in the 30–200 g weight range.     

Neutron activation analysis of U,Th, K and Rb in archaeological samples from Guayabo (Costa Rica) prior to thermoluminescent dating

Neutron activation analysis has been applied to evaluate the concentrations of U, Th, K and Rb in archaeological samples in view of precise thermoluminescent (T.L.) dating. The experimental conditions including the timing and the Ge detector characteristics are examined. For U and Th, the determinations have been made through both the short radioisotopes (²³⁹U and²³³Th) or through the long-lived daughter nuclei (²³⁹Np and²³³Pa). A factor of 7 between the calculated and observed yields for U is found and discussed. The simultaneous measurement of the 4 elements of interest in samples of about 200 mg is easy achieved.     

Neutron activation analysis of CdxHg1-xTe

A procedure has been developed for the analysis of Cd_xHg_1-xTe samples; the elements to be determined /Na, K, Cr, Mn, Cu, Co, Zn, As, La/ are separated by chromatography after neutron activation. The detection limit varies between 1×10^–5% and 5×10^–8%. A comparison of the calculation and semiempirical methods of the screening effect determination has been made.     

Determination of a strong organic ligand dissolved in seawater: Thorium-complexing capacity of oceanic dissolved organic matter

Studies have been made of loose water tritium (LWT) distribution and behavior in the soil samples taken from the region within a radius of 2 km to the HWRR stack of CIAE. The analytical results show that the LWT concentrations in most soil samples of the region are in the range from 24.8 Bq/l (3.6 Bq/kg) to 116 Bq/l (16.0 Bq/kg) with an average value of 58.1±24.8 Bq/l (10.3±4.5 Bq/kg). There are two areas with a higher LWT content; the first one (4.61 · 10⁴ m²) is located near HWRR with ahighest LWT concentration of 287 Bq/l (55.8 Bq/kg) and the second one (3.27 ·10⁵ m²) is located near Lab. A with a highest LWT concentration of 2.35 · 10⁴ Bq/l (2.56 · 10³ Bq/kg). It is estimated that the LWT inventories deposited in soil of the two areas are about 1.52 · 10⁹ Bq and 1.42 · 10¹⁰ Bq, respectively. The analytical results have been evaluated by comparing the possible tritium intake of the human body with the annual limit of intake recommended by ICRP, it can be concluded that the operations of all the nuclear facilities releasing tritium in CIAE are safe without causing any notable tritium contamination.     

Preconcentration and determination of rare-earth elements in iron-rich water samples by extraction chromatography and plasma source mass spectrometry (ICP-MS)

A 100-fold preconcentration procedure based on rare-earth elements (REEs) separation from water samples with an extraction chromatographic column has been developed. The separation of REEs from matrix elements (mainly Fe, alkaline and alkaline-earth elements) in water samples was performed loading the samples, previously acidified to pH 2.0 with HNO₃, in a 2 ml column preconditioned with 20 ml 0.01 M HNO₃. Subsequently, REEs were quantitatively eluted with 20 ml 7 M HNO₃. This solution was evaporated to dryness and the final residue was dissolved in 10 ml 2% HNO₃ containing 1 μg l⁻¹ of cesium used as internal standard. The solution was directly analysed by inductively coupled plasma mass spectrometry (ICP-MS), using ultrasonic nebulization, obtaining quantification limits ranging from 0.05 to 0.10 ng l⁻¹. The proposed method has been applied to granitic waters running through fracture fillings coated by iron and manganese oxy-hydroxides in the area of the Ratones (Cáceres, Spain) old uranium mine.     

Advances in 14 MeV neutron activation analysis by means of a new intense neutron source

A new intense 14 MeV neutron generator with cylindrical acceleration structure has been put in operation at the GKSS Research Center Geesthacht. The sealed neutron tube is combined with a fast pneumatic rabbit system with particular capabilities for neutron activation analysis involving shortlived reaction products. The sample transfer time is less than 140 ms. The maximum neutron flux available for activation is 5.2·10¹⁰ n/cm²s. Theoretical sensitivity predictions made in a previous study have been verified for some important trace elements. As a first application, samples of freeze-dried suspended matter and fishes of the Elbe river were analyzed.     

Instrumental neutron activation determination of Pt, Ru, Ir, Sc, Cr, Fe, Co, La, Ce, Nd, Sm, Yb, Lu, Hf and Ta employing CIRUS reactor as a thermal neutron source

An accurate and simple method has been developed for the determination of Pt, Ru, Ir and other elements employing instrumental neutron activation analysis (INAA). Nondestructive analysis has been carried out for the determination of these elements in different rock samples such as Dolerite, Dyke Dolerite, Country Basalt, Hyaloclastite, Trachyte, Ijolite, Spillite, Diorite and Lamprophyre from various locations like Daman, Tapti, Murud, Talasari, Ranala and Bassein in Maharashtra state. High flux provided by the CIRUS reactor (1×10¹³ n cm^–2s^–1) has been used for thermal neutron bombardment followed by radioassaying of the (n,) products on a HPGe detector coupled to a PC-based MCA unit.     

Neutron activation analysis of iodine in soil

A simple pre-irradiation procedure for the separation of iodine from soil has been developed. A soil sample was heated in a quartz tube for 15 min at about 900 °C. The evaporated iodine was collected in activated charcoal, which was produced from phenol resin with low impurities. The charcoal, with sorbed iodine, was irradiated by neutrons and the¹²⁸I produced was measured. A successful elimination of the background radioactivity due to the matrix elements was possible with this separation procedure. The detection limit by this method for soil samples was about 0.1 mg/kg (dry). The method has been applied to analyze selected soil samples.