Neutron Activation Analysis Procedure Research Articles

Magnesium-based alloys analyses by nuclear techniques

Magnesium-based alloys have been proposed for used in temporary biomaterials in the applications that request their biocompatibility and degradability. Analyses of these alloys are of great interest to verify if their element composition is within the product specification and also to evaluate the impurities that may cause toxic effects to the human health or influence in their corrosion processes. In this study, nuclear techniques of neutron activation analysis (NAA) and wavelength dispersive X ray fluorescence spectrometry (WD XRFS) were applied in the analyses of two magnesium-based alloys: commercially pure magnesium (CP-Mg) and AZ31 alloy. The NAA procedure consisted of irradiating aliquots of sample and synthetic element standards followed by measurements using a HGe detector and the WD XFRS was carried out using the Model RIX 3000 X-ray spectrometer. In the CP-Mg sample several element impurities were quantified. In the AZ31 alloy, the alloying element mass fractions were within the product specification and the impurities of As, La, Na and Sb were also quantified. Nickel and sulfur were quantified only by WD XFRS. The Horwitz method was a good parameter to evaluate the repeatability of the results in Al, Mg, Mn and Zn determinations. In conclusion, the results indicated the viability of using NAA and WD XFRS in the analyses of magnesium-based materials mainly due its multielement determinations, precision of the results, quantification of elements in a wide range of mass fractions and the lack of need for sample dissolution.

Validation of k0-Standardization Procedure of Instrumental Neutron Activation Analysis at Ghana Research Reactor-1 Facility for the Determination of Rare Earth Elements

Validation of k0-Standardization Procedure of Instrumental Neutron Activation Analysis at Ghana Research Reactor-1 Facility for the Determination of Rare Earth Elements

Evaluation of the spatial variability of the elements in tree barks used as biomonitors of atmospheric pollution

Tree barks have proven to be a valuable source of information on air quality. Nowadays, studies with this biomonitor are constantly being developed. However, data of several factors that affect the accumulation of the pollutants in the barks, such as bark porosity, duration of the deposition on the bark and dispersion or variability of pollutants in a defined area, are scarce in the literature. The aim of this study was to evaluate the spatial variability of chemical elements concentrations accumulated on Sibipiruna (Cenostigna pluviosarum) barks in order to examine their aerial dispersion in two small urban areas of the Metropolitan Area of São Paulo. The neutron activation analysis (NAA) applied in the analyses consisted of irradiation the aliquots of the sample together the synthetic element standards at the IEA-R1 nuclear reactor. Concentrations of the As, Br, Ca, Co, Cr, Cs, Fe, K, La, Mn, Rb, Sb, Sc, V and Zn were determined in tree barks using short and long irradiations. Results obtained in the analyses of the tree bark samples indicated that the variability of element concentrations depends on the element, study area and numbers of trees. The variability of element concentrations in general was higher for elements presenting low concentrations. Quality control of the analytical results was evaluated by the analysis of INCT-MPH-2 Mixed Polish Herbs Certified Reference Material and these results presented good accuracy with values of standardized difference or |ζ score| ≤ 2, indicating that the procedure of NAA applied is suitable for the analyses.

Experimental design and z-score results are useful tools for optimizing instrumental neutron activation analysis procedures

In this study 2k experimental designs were used for the optimization of an instrumental neutron activation analysis method for the determination of bromine, chlorine, magnesium, manganese, potassium, sodium and vanadium in biological matrix materials. Depending on radionuclide half-lives, 23 or 24 experimental designs were used with irradiation time, sample–detector distance, counting time and sample decay time as factors. Gamma ray spectrometer, comparator mass fraction and sample mass were kept constant. Optimized irradiation and measurement conditions were established based on the experimental design results that used z-scores as response on a reference material for the various elements and experimental conditions.

Determination of gold in biological materials by radiochemical neutron activation analysis

A radiochemical neutron activation analysis procedure was developed for the determination of trace amounts of gold in biological materials. The procedure was realized with irradiation of reference and test samples in a nuclear reactor, selective and quantitative separation of gold using inorganic MnO2 Resin and gamma-ray spectrometric measurement of 198Au. The method is characterized by a low limit of detection of gold at ng g−1 level. Results shows that the method can be applied to the determination of trace amounts of gold in tissues for medical research.

Neutron activation analysis for the characterization of seawater uranium adsorbents

This work details the development of an iterative neutron activation analysis (NAA) based workflow to precisely quantify metal ion uptake in an adsorbent. The workflow is iterative because it explores the dependence between independent variables defining the adsorbent fabrication procedure and the time-dependent uptake. It can be adapted to other adsorbents provided they have an affinity for ions which are amenable to efficient quantification using NAA. For this work, the ability of silver nanoparticles to mitigate the negative effects of biofouling on uranium transfer to an adsorbent was ultimately of interest, and hence motivates the development of this method. The limits of U detection and quantification were found to be 0.609 and 3.01μgg−1, respectively; these were obtained using modest irradiation and counting times. The uncertainties arising from the NAA procedure were no more than 9.9%, far smaller than other sources of uncertainty present in the analysis. These results provided solid evidence that adsorbent shape and structure, rather than uniformity of composition, drives variability in adsorption of uranium.

HPGe detector full-energy peak efficiency calculation for inhomogeneously activated samples

We present and evaluate a program for the semi-empirical calculation of the full-energy peak efficiency of a hyper-pure germanium detector, by using the efficiency transfer method. Using simple Monte-Carlo integration and constructive solid geometry, we are able to calculate the effective solid angle for a wide range of HPGe detector and sample geometries. However, the main advancement is including in our calculations the inhomogeneity of the sample activity, caused by the inhomogeneous neutron flux when performing neutron activation analysis (NAA). This reduces systematic error in the standard procedure of NAA. To increase usability, the input and output file formats used are compatible with the program SOLANG, which belongs to the Kayzero for Windows (KayWin®) software.

Application of neutron activation analysis to micro gram scale of solid samples

An instrumental neutron activation analysis (INAA) procedure for analyzing extremely small samples was developed and applied to two kinds of extraterrestrial samples. A few mg of the Allende meteorite as well as the JB-1 basalt can work well as a reference sample for a relative method. To evaluate the applicability of this INAA procedure, detection limits are presented and compared with the elemental contents in a potential sample to be analyzed. The possibility of reuse of neutron-irradiated samples for mass spectrometry was noted by indicating degree of increase in isotopic abundance for noble gas and long-lived radioactive nuclides.

Spatial distribution of neutron flux in geological larger sample analysis at CDTN/CNEN, Brazil

Iron monitor wire was used to evaluate the neutron flux gradients inside 5 g-geological sample during irradiation. The spatial distribution for thermal flux was about 2 %/cm for radial and axial gradients and about 5 %/cm for radial and 2.5 %/cm for axial gradients for fast neutrons. The results were evaluated using reference material IAEA-SOIL-7 analysed as small and larger samples and tested with calculating E n numbers. This test pointed out that all results were consistent within a 95 % confidence interval. The contribution of the neutron flux gradients may be reduced for larger sample using the standard procedure of the k 0-instrumental neutron activation analysis.

Mercury mass measurement in fluorescent lamps via neutron activation analysis

Abstract Mercury is an essential component of fluorescent lamps. Not all fluorescent lamps are recycled, resulting in contamination of the environment with toxic mercury, making measurement of the mercury mass used in fluorescent lamps important. Mercury mass measurement of lamps via instrumental neutron activation analysis (NAA) was tested under various conditions in the LVR-15 research reactor. Fluorescent lamps were irradiated in different positions in vertical irradiation channels and a horizontal channel in neutron fields with total fluence rates from 3×10 8 cm −2 s −1 to 10 14 cm −2 s −1 . The 202 Hg(n,γ) 203 Hg nuclear reaction was used for mercury mass evaluation. Activities of 203 Hg and others induced radionuclides were measured via gamma spectrometry with an HPGe detector at various times after irradiation. Standards containing an Hg 2 Cl 2 compound were used to determine mercury mass. Problems arise from the presence of elements with a large effective cross section in luminescent material (europium, antimony and gadolinium) and glass (boron). The paper describes optimization of the NAA procedure in the LVR-15 research reactor with particular attention to influence of neutron self-absorption in fluorescent lamps.

THE USE OF NEUTRON ACTIVATION ANALYSIS IN THE BIOMONITORING OF TRACE ELEMENT DEPOSITION IN THE OPOLE PROVINCE

Abstract The neutron activation analysis procedure was used to determine the concentration of 42 elements: Na, Mg, Al, Cl, K, Ca, Sc, V, Cr, Mn, Fe, Ni, Co, Zn, As, Se, Br, Rb, Sr, Zr, Nb, Mo, I, Ag, Cd, Sb, Ba, Cs, La, Ce, Nd, Sm, Eu, Tb, Yb, Hf, Ta, W, Au, Hg, Th, and U accumulated in mosses sampled for testing in September and October 2011 in the Opole Province (Southern Poland). Samples of different moss species were collected near the intersections of the grid lines marked on the map of the province. The distance between the points was approximately 20 km. The analysis of the results made it possible to identify the places of increased deposition of element-pollutants and to indicate the potential sources of emission. Factor analysis revealed four components, two of which are of definite anthropogenic origin. The possible sources of elements are local industry and farming, and distant heavy industry complexes. The results have demonstrated the increased content of Cr, Cd, Hg, and U in moss samples collected in agricultural areas located in the southern part of the province. It has been concluded that the industrial areas of Rybnik and Ostrava and Karvina Coal Basin may be the potential source of emission of these elements.

Determination of 129I in biomonitors collected in the vicinity of a nuclear power plant by neutron activation analysis

Neutron activation analysis (NAA) was used to determine 129I and the 129I/127I ratio in bovine thyroid, moss, and river sediment samples collected in the vicinity of the Temelin nuclear power plant (NPP) in south Bohemia. The NAA procedures comprised pre-irradiation separation of 129I by combustion of the samples in the stream of oxygen at 1,000 °C and trapping the liberated iodine in a LiOH/(NH4)2SO3 solution. Post-irradiation separation of 130I produced by the reaction 129I(n,γ)130I was carried out by extraction of elementary iodine with chloroform followed by precipitation of PdI2. Nondestructive, epithermal NAA was used to determine 127I employing the 127I(n,γ)128I reaction. The results showed that mean values of 129I and the 129I/127I ratio in the bovine thyroids varied from 22 to 61 mBq kg−1 (dry mass) and 2.8 × 10−9 to 5.4 × 10−9, respectively. These values are close to the lower end of results reported from various regions non-polluted with 129I. No significant differences were found between 129I concentrations and the 129I/127I ratios in the bovine thyroids collected prior to the start and after several years of operation of the NPP. The mean value and standard deviation of 129I in mBq kg−1, dry mass and the 129I/127I ratio in moss Pleurozium schreberi were 23 ± 16 and 2.3 × 10−9, respectively, whereas values of 129I in the river sediments were below 8–10 mBq kg−1 (dry mass) after several years of the NPP operation.

Improving neutron activation analysis accuracy for the measurement of gold in the characterization of heterogeneous catalysts using a TRIGA reactor

To measure the gold content of a catalyst accurately, neutron activation analysis (NAA) is one of the methods of choice. NAA is preferred for such heterogeneous catalysts because: (1) it requires minimal sample preparation; (2) NAA provides consistent and accurate results; and (3) in most cases results are obtained much quicker than competing methods. NAA is also used as a referee for the other elemental techniques when results do not fall within expected statistical uncertainties. However, at very high gold concentrations, applying NAA to determine the gold in a heterogeneous catalyst is more challenging than a routine NAA procedure. On the one hand, the neutron absorption cross section for gold is very high, resulting in significant self-shielding related errors. On the other hand, gold exhibits low energy resonance neutron absorptions. In this application the self-shielding minimization effort was handled more rigorously than the classic suppression of neutron flux within a specimen. This non-routine approach was used because: (1) for most applications, high accuracy, <3 % relative, is desired, (2) the low energy resonances of gold make its neutron reaction rate complex and (3) the TRIGA reactor flux profile used in this study contains both thermal and significant epithermal neutron fluxes. Accuracy and precision, using this new approach, are expected to improve from 15 % to better than 3 % relative uncertainty. This has been accomplished through a rigorous assessment of the observed effects of low energy resonance on the neutron flux spectral shape within the sample and designing an experiment to minimize the effects.

Elemental analysis of a single-wall carbon nanotube candidate reference material

A material containing single-wall carbon nanotubes (SWCNTs) with other carbon species, catalyst residues, and trace element contaminants has been prepared by the National Institute of Standards and Technology for characterization and distribution as Standard Reference Material SRM 2483 Carbon Nanotube Soot. Neutron activation analysis (NAA) and inductively coupled plasma mass spectrometry (ICP-MS) were selected to characterize the elemental composition. Catalyst residues at percentage mass fraction level were determined with independent NAA procedures and a number of trace elements, including selected rare earth elements, were determined with NAA and ICP-MS procedures. The results of the investigated materials agreed well among the NAA and ICP-MS procedures and good agreement of measured values with certified values was found in selected SRMs included in the analyses. Based on this work mass fraction values for catalyst and trace elements were assigned to the candidate SRM.

A new method for the analysis of titanium, barium, and arsenic in obsidian via epithermal neutron activation analysis

A new instrumental epithermal neutron activation analysis procedure to quantitatively determine titanium, barium, and bromine in obsidian with improved sensitivity has been developed. The advantage of epithermal activation for Ti, Ba, and Br is demonstrated with multiple geological standards and the ability to determine arsenic in obsidian is demonstrated. The results for titanium are compared to previous electron-microprobe results for Kenyan obsidian.

Determination of rare earth and other trace impurities in high purity gadolinium oxide

Extensive use of gadolinia for different high technology applications such as infrared absorbing automotive glass, petroleum cracking catalyst, gadolinium-yttrium garnets and color TV tube phosphors requires a precise characterization of the material. A radiochemical neutron activation analysis (RNAA) procedure has been employed to investigate 16 trace impurities in high purity gadolinia. RNAA procedure enhanced the sensitivity of the technique. The concentrations of trace impurities ranged from 20 ng/g to 34 µg/g. The impurity contents were found to be low; therefore, their deleterious effects would be negligible.

Challenges and successes in the use of neutron activation analysis procedures for value assignment of animal serum and bovine liver Standard Reference Materials

Analyses for value assignment in the renewal Standard Reference Materials® SRM 1598a Animal Serum and SRM 1577c Bovine Liver included extensive characterization by neutron activation analysis (NAA). Conventional instrumental NAA procedures were complemented by pre-irradiation chemical separations for the determination of Al, V, Mn, and Cu, radiochemical separations for the determination of Ag, As, Cd, Cr, Cu, Mo, Sb, and Se, and the use of (anti-) coincidence gamma-ray spectrometry systems for the instrumental determination of Ag, Cr, and Hg. The previous materials, SRMs 1598, 1577, and 1577b, were analyzed together with the new materials for quality control.

Arsenic speciation: HPLC followed by ICP-MS or INAA

Sensitivities for the measurement of four arsenic species, AsIII, AsV, 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.

A pre-concentration neutron activation analysis method for the determination of 232Th utilizing a dry-tube irradiation facility

A revized method for determining 232Th using a pre-concentration neutron activation analysis (PCNAA) procedure was developed to accommodate irradiation in a dry irradiation tube environment. 232Th extracted by ion-exchange from a sample was electrodeposited onto 5/8″ diameter vanadium planchets, which are arranged in a stack and irradiated in the dry tube central irradiation facility (CIF) of the reactor. The higher neutron fluence of this facility improved sensitivity by approximately 37%, however, the higher temperatures required modifications to the irradiation procedure. Because the heat in the CIF would melt the plastic spacers used in the original method, a tube of high-purity quartz was used to contain samples, and high purity quartz spacers were used to separate the vanadium planchets during the irradiation. Test irradiations have determined that no significant transfer occurred from the disks to the silica disks and no significant variation in the neutron flux was observed. Finally, a thin film barrier was tested for its ability to reduce recoil contamination from 229Th onto the detector during alpha spectroscopy. The film was shown to reduce contamination to levels indistinguishable from normal background.

The application of neutron activation analysis, scanning electron microscope, and radiographic imaging for the characterization of electrochemically deposited layers of lanthanide and actinide elements

Lanthanide and actinide targets are prepared at the University of Mainz by molecular plating, an electrochemical deposition from an organic solvent, for heavy-ion reaction studies at GSI. To acquire information about deposition yield, target thickness, and target homogeneity, the following analysis methods are applied. With neutron activation analysis (NAA) the deposition yield and the average thickness of the deposited material is determined. We report on the analytical procedure of NAA performed subsequent to the molecular plating process. Scanning electron microscope (SEM) is used to determine the morphology of the target surfaces. In combination with energy dispersive X-ray spectrometer (EDS), we also could obtain qualitative information about the chemical form of the deposited material. So far, gadolinium, samarium, holmium, and uranium targets have been investigated with SEM/EDS. With radiographic imaging (RI), targets of uranium prepared by molecular plating and by vacuum vaporization are investigated. This method is suitable to obtain information about the spatial distribution, the homogeneity, and the thickness of the target layer deposition.