Different methodologies in neutron activation to approach the full analysis of environmental and nutritional samples

Different methodologies of neutron activation analysis (NAA) are now available at the Technological and Nuclear Institute (Sacavém, Portugal), namely Compton suppression, epithermal activation, replicate and cyclic activation, and low energy photon measurement. Prompt gamma activation analysis (PGAA) will be implemented soon. Results by instrumental NAA and PGAA on environmental and nutritional samples are discussed herein, showing that PGAA — carried out at the Institute of Isotope Research (Budapest, Hungary) — brings about an effective input to assessing relevant elements. Sensitivity enhancement in NAA by Compton suppression is also illustrated. Through a judicious combination of methodologies, practically all elements of interest in pollution and nutrition terms can be determined.     

Inteferences in neutron and photon activation analysis

The effect of following interferences was quantitatively assessed in terms of interference factor by irradiating samples together with highly pure reagents at two reactor sites of diferent neutron spectra and fluxes for neutron activation analysis (NAA) and an electron LINAC for photon activation analysis (PAA). The interfering reactions studied are 91) fast neutron-induced reactions, (2) uranium fission (3) (n,γ) reactions of other target elements in NAA, and (4) reactions induced by secondary neutrons in PAA. Corrections for these interferences were successfully applied to the activation analysis of some geological reference rock samples and biological samples.     

Application of NAA to air particulate matter collected at thirteen sampling sites in eight Asian countries: A collaborative study

Air particulate matter (APM) samples (PM_2.5 and PM_10–2.5) were collected at 13 sampling points in 8 Asian countries and their chemical compositions were determined by using neutron activation analysis (NAA) with the k ₀-standardization method in addition to conventional comparative method of NAA. Analytical data showed that mass concentration and elemental composition of the APM collected are variable in terms of time and space, and are related to the characteristics of the sampling sites concerned. NAA was proved to be highly effective for the regional characterization of APM in chemical composition.     

Nuclear activation methods for the characterization of fossil fuels

A review is presented on the use of neutron activation analysis (NAA) for the analyses of coal, oil shale, tar sands and petroleum. Fast NAA has been widely used for the determination of oxygen, and to a limited extent, of other elements such as nitrogen and silicon. Reactor NAA followed by instrumental counting, and in specific cases, after radiochemical separations is discussed. Thermal and epithermal neutrons are both used. Limited use of the²⁵²Cf source has been made in fuel analysis. A complementary technique to NAA is the photon-activation analysis with linear accelerator. It can determine over thirty elements, many of them not possible to do by NAA. Round-robin analyses of standard coal, fly ash, or oil shale samples indicate nuclear activation methods are comparable in accuracy and precision to X-ray fluorescence or atomic spectrometric methods for most elements.     

Methodological developments and applications of neutron activation analysis

The paper reviews the author’s experience acquired and achievements made in methodological developments of neutron activation analysis (NAA) of mostly biological materials. These involve epithermal neutron activation analysis, radiochemical neutron activation analysis using both single-and multi-element separation procedures, use of various counting modes, and the development and use of self-verification principle. The role of NAA in the detection of analytical errors is discussed and examples of applications of the procedures developed are given.     

The determination of selenium in biological material by thermal neutron activation analysis and atomic absorption spectrometry

Neutron activation analysis and atomic absorption spectrometry (graphite furnace) methods for the analysis of selenium in human tissue are described. The sensitivity (10–30 ng/sample), accuracy and precision are of the same order for both techniques and the choice can only be made on grounds of urgency or convenience. AAS should be chosen for the analysis of wet tissue or the urgent analysis of small numbers of dry tissue. NAA should be chosen for the analysis of large numbers of dry tissue samples where time is not important. The selenium concentration of human liver is shown to be in the region of 1 to 2 ppm (dry weight). Selenium may be lost from tissue during freeze drying if the samples are not maintained at −35°C.     

Characterization of serpentine: a potential nuclear shielding material

The use of serpentine as a potential nuclear shielding material necessitates a chemical quality control of the samples before its use in reactors. With this in view, characterization of these mineral samples was carried out using inductively coupled plasma atomic emission spectrometry (ICP-AES) and Instrumental neutron activation analysis (INAA) methods. The analytical results obtained by both ICP-AES and NAA techniques were found to be comparable. Na, Cr, Co, Zn, and Cu were found to be present in all samples of Indian origin while Ga, Ag, Ni, and Cd were found to below the limits of detection. A comparison on the detection limits of elements of interest was also carried out by both the analytical techniques and found to be in good agreement. An infrared spectroscopic investigation was also carried out on all the mineral samples. Bands at 3,689 and 3,648 cm⁻¹ were attributed to inner and outer hydroxyl stretching of Mg–OH, respectively. The weak and broad band centered around 3,416 cm⁻¹ was assigned due to the stretching vibrations of the adsorbed water molecules while three bands at 1076, 1022 and 968 cm⁻¹ were prescribed to the vibrations of the SiO₄ tetrahedra.     

Arsenic speciation: HPLC followed by ICP-MS or INAA

Sensitivities for the measurement of four arsenic species, As^III, As^V, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), in environmental waters and rice extracts by a new neutron activation analysis (NAA) method using pre-separation of the species by liquid chromatography were determined. A manual fraction collection was used to isolate the species, followed by instrumental neutron activation analysis procedures. The sensitivities determined for arsenic species in the samples varied from 1.21 to 1.47 ng per vial or about 30 μg·L⁻¹ in sample solutions which translates to about 900 ng arsenic per gram of rice for our HPLC-NAA experiments.     

Analytical radiochemistry of neutron activated samples in practice

Analytical radiochemistry of neutron-activated samples, as practiced during past decades at the Jo?ef Stefan Institute Ljubljana, is outlined. The paper reviews achievements made in both elemental analysis and analyses of long-lived radionuclides, in variety of sample types. The presented analytical procedures include application of diverse chemical separations, multiple irradiations of samples, use of various nuclear reactions and detection modes for particular measurands, and determination of elements that are difficult to be determined by neutron activation analysis (NAA). Useful practical applications of neutron-activated tracers for chemical yield determinations, as unique feature of radiochemical NAA in comparison with non-nuclear analytical methods, are also addressed.     

Application of different activation analysis techniques for determination of trace elements in human blood

One of the requirements of stable isotope tracer technique is detection of two isotopes of same element. It is preferable to use instrumental techniques in order not to contaminate the samples. Different instrumental nuclear techniques namely neutron activation analysis (NAA), photon activation analysis (IPAA), and prompt gamma ray activation analysis (PGAA) were tried on human blood samples. The techniques were found to be complementary to each other, NAA being the most sensitive of the three. Zinc is choosen for validation work among the three feasible elements (Zn, Cr, Se) for stable isotope tracer technique. As NAA was not sufficient to detect two isotopes of Zn, a radiochemical separation scheme was developed later.     

Determination of silver in biological reference materials by neutron activation analysis

Silver in selected, predominantly biological, reference materials (NIST SRM 1515, 1547, 1549, 1566a, 1571, 1577b, 2704, CTA-OTL-1, and Bowen’s Kale) was determined using neutron activation analysis (NAA) in two different analytical modes: instrumental NAA with epithermal neutrons (ENAA), and NAA with radiochemical separation (RNAA). The ENAA mode was based on long-time 5-hour irradiation of samples in a special Cd lined box with counting after 8-month decay. The RNAA procedure consisted in 20-hour irradiation of samples, their decomposition/dissolution by alkaline-oxidative fusion, and precipitation of AgCl including several purification steps. Both methods provided Ag contents in the analyzed reference materials consistent with certified and/or literature values down to the ng·g⁻¹ level.     

Modeling a gamma spectroscopy system and predicting spectra with Geant-4

An activity predictor software was previously developed to foresee activities, exposure rates and gamma spectra of activated samples for Radiation Science and Engineering Center (RSEC), Penn State Breazeale Reactor (PSBR), Neutron Activation Analysis (NAA) measurements. With Activity Predictor it has been demonstrated that the predicted spectra were less than satisfactory. In order to obtain better predicted spectra, a new detailed model for the RSEC NAA spectroscopy system with High Purity Germanium (HPGe) detector is developed using Geant-4. The model was validated with a National Bureau of Standards certified ⁶⁰Co source and tree activated high purity samples at PSBR. The predicted spectra agreed well with measured spectra. Error in net photo peak area values were 8.6–33.6%. Along with the previously developed activity predictor software, this new model in Geant-4 provided realistic spectra prediction for NAA experiments at RSEC PSBR.     

A versatile charged particle activation technique for the analysis of the noble metals

The general usefulness of neutron activation analysis (NAA) for samples containing the platinum group elements (PGE) and Au, either as major or trace consituents, is discussed. Charged particle activation is shown to be a viable or complementary alternative. Proton (6–10 MeV) and alpha particle (9–15 MeV) beams, produced in a Tandem van de Graaff accelerater, have been established to be the most effective choice. By taking advantage of the Coulomb Barrier Effect and the fact that many charged particle induced reactions have relatively large threshold values, the same instrumental technique can be applied, with minor modifications, to a wide range of materials.     

Characterization of soil,sediment, and wastewater samples from hydraulic fracturing processes using the comparative NAA method

Regulatory monitoring of oil and gas development requires the accurate multi-elemental analysis of wellbore samples on a regular basis. In this study, an unconventional method, comparative neutron activation analysis (comparative NAA), was applied for the multi-elemental characterization of solid and liquid hydraulic fracturing samples at the ppm level. The obtained values from three wastewater samples were compared with the most probable values determined via an inter-laboratory study, which involved 15 different laboratories from the United States, Canada, and Germany. The comparison showed that 15 out of 19 comparative NAA trace element concentration values were considered acceptable, providing a new technique to determine elemental concentrations in high salinity hydraulic fracturing samples.

     

Pushing the limits of NAA: Accuracy,uncertainty and detection limits

This paper describes some highlights from the author’s efforts to improve neutron activation analysis (NAA) detection limits through development and optimization of radiochemical separations, as well as to improve the overall accuracy of NAA measurements by identifying, quantifying and reducing measurement biases and uncertainties. Efforts to demonstrate the metrological basis of NAA, and to establish it as a “Primary Method of Measurement” will be discussed.     

Metrological role of neutron activation analysis. IA. Inherent characteristics of relative INAA as a primary ratio method of measurement

In a series of three papers, the inherent characteristics of relative instrumental neutron activation analysis (INAA) as a primary ratio method of measurement, the unique functions of parametric INAA as an ideal back-up method of the relative INAA, and the valuable role of INAA in characterization of sampling behavior of individual elements in certified reference materials (CRMs) will be discussed. In this paper, the first of the series, the uncertainty evaluation and the traceability of values measured by neutron activation analysis (NAA), especially instrumental NAA (INAA), will be described to demonstrate the method at its ”the state-of-the-art” level can meet CCQM criteria for a primary ratio method. The scope and examples will be given. Received: 19 March 2001 Accepted: 2 October 2001     

New Developments in Activation Analysis for Material and Environmental Sciences

Activation analysis in general and mainly reactor neutron activation analysis (NAA) has been used extensively for measuring trace elements in high purity materials, particularly semiconductor materials. The advantages of NAA in determination of trace elements differ from one semiconductor material to another. For all of them the inherent properties of activation analysis especially those of non contamination with the reagents, low blanks and high sensitivity are the reasons for the choice of NAA as the main analytical procedure. These inherent properties are essential for analysis of high-purity materials where concentrations of ppb's and sub ppb's have to be measured. NAA is specially suitable for the determination of trace elements in silicon due to the very short lived very low activity induced by neutron reaction in silicon. This enables easy instrumental (i.e. without chemical separations) determination of trace elements in silicon. In the HFR reactor at Peten, Netherlands, a special facility was constructed for irradiation of silicon samples of Philips, in which silicon wafers of up to 15 cm diameter can be irradiated with 4 × 10¹³n. cm^?2. sec^?1 and the irradiation is done for 72–96 hours. using large Ge(Li) detectors (100 to 150cc) and long counting time (8–16 hours) they measured 22 elements in concentrations below ppb and 10 others between ppb and 300 ppm. Trace elements in germanium have been determined both instrumentally after very long decay time (100 days) or after short decay time removing the activities from the matrix by chemical separation. Trace elements in GaAs are determined only after chemical separtion. Several other semiconductor material such as Sc, Te, GaP and CuInS₂ were also determined by NAA. Some trace elements cannot be determined by neutron activation. Carbon, nitrogen and oxygen are determined by activation with protons, alphas or ³He particles. Boron and hydrogen are determined by prompt emission induced by charged particle activation, which gives not only the total concentration but also the depth profile. Carbon, nitrogen, oxygen and phosphorus were also determined by prompt proton activation analysis. The environmental samples studied by activation analysis can be divided into three categories: atmospheric aerosols, water samples and solid wastes. NAA of atmospheric aerosols have been used for their posible toxicological hazards, their source identification and for studies of atmospheric transport processes.     

U determination in environmental samples by delayed neutron activation analysis in Korea

A delayed neutron counting system has been implemented at the HANARO research reactor in 2007. Thermal neutron flux measured at the NAA #2 irradiation hole coupled to the delayed counting system, was higher than 3 × 10¹³ n cm⁻² s⁻¹. The delayed neutron counting system is composed of 18 ³He detectors which are divided into three groups with six detectors and the collected signals of each group are processed to a digital signal. The count numbers were measured with the uranium mass by using NIST SRMs under fixed analytical condition and their correlation could be determined. Finally, delayed neutron activation analysis has been carried out for the determination of uranium mass fraction in the collected environmental samples.     

Analysis of the Arctic aerosol for a ten year period using various neutron activation analysis methods

During the past decade we have determined the concentrations of a variety of trace elements in the Arctic aerosol by using themal and epithemal neutron activation analysis (NAA). More recently we have employed Compton suppression NAA to lower the detection limits for radionuclides that are characteristic of single or mainly single gamma-ray emission. Using these various methods, we have been able to use elements such as indium and silicon. Furthermore we have achieved extremely low detection limits for iodine, arsenic and antimony. The usefulness of these NAA methods are discussed in a large sampling program that incorporates more than one thousand samples.     

The determination of chromium-50 in human blood and its utilization for blood volume measurements

Possible relationships between insufficient blood volume increases during pregnancy and infant mortality could be established with an adequate measurement procedure. An accurate and precise technique for blood volume measurements has been found in the isotope dilution technique using chromium-51 as a label for red blood cells. However, in a study involving pregnant women, only stable isotopes can be used for labeling. Stable chromium-50 can be determined in total blood samples before and after dilution experiments by neutron activation analysis (NAA) or mass spectrometry. However, both techniques may be affected by insufficient sensitivity and contamination problems at the inherently low natural chromium concentrations to be measured in the blood. NAA procedures involving irradiations with highly thermalized neutrons at a fluence rate of 2·10¹³ n·cm^–2·s^–1 and low background gamma spectrometry are applied to the analysis of total blood. Natural levels of chromium-50 in human and animal blood have been found to be <0.1 ng/ml; i.e., total chromium levels of <3 ng/ml. Based on the NAA procedure, a new approach to the blood volume measurement via chromium-50 isotope dilution has been developed which utilizes the ratio of the induced activities of chromium-51 to the iron-59 in three blood samples taken from each individual, namely blank, labeled and diluted labeled blood.