Determination of some elements by epithermal neutron activation analysis for the Arctic aerosol

Summary We have determined nineteen trace elements in 685 aerosol filter samples collected during 1964-1978 in northern Finland by the Finnish Meteorological Institute. In this paper we present some procedures and results for very short (~25 s), short (~3-54 min), and medium (12-35 h) lived isotopes as determined by epithermal NAA in conjunction with and without Compton suppression. Elements with a I_γ/σthratio are favorable to be determined by epithermal NAA. Silver was determined by a one minute epithermal irradiation because of a very short ¹¹⁰Ag half-life. Antimony, arsenic, cobalt, bromine, indium, iodine, potassium, silicon, tin, tungsten, and zinc were determined by a ten minute epithermal irradiation. For silver determination, samples were counted without transferring the filter from the irradiated vial, however, for ten minute irradiation all samples were transferred to a non-irradiated vial and counted both in the normal and Compton mode by the HPGe gamma-spectrometry system with a decay time of about 10 minutes and counting time of 15 minutes. Each day a maximum of 16 samples were irradiated and immediately following the short counting, these samples were loaded into an automatic sample changer in sequence of irradiation and counted for an hour in both normal and Compton modes. This has proven to be an extremely cost effective measure thus reducing the need to employ long-lived NAA to analyze other elements such as Ag, Co, Sn and Zn and Ag for air pollution source receptor modeling.     

Tin in biological materials: Comparison of different separation and detection modalities

Evaluating the nuclear properties for the detection of different isotopes of tin revealed^117mSn (13.6 d half life and 158.44 keV gamma-ray) to be the most sensitive for a 12 h irradiation and 8 d decay period. Counting of the extracted tin samples with a Compton suppression spectrometer was superior to normal gamma counting by a factor of about 3.5.     

Comparison of NAA methods to determine medium-lived radionuclides in NIST soil standard reference materials

In order to determine the elemental concentrations of three new soil standard reference materials SRMs 2709, 2710 and 2711 from the National Institute of Standards and Technology (NIST), a comparative study of different medium-lived neutron activation analysis methods was carefully performed. Three irradiation conditions (1-hour thermal, 1-hour epithermal and 5-minute epithermal) and two counting modes (normal and Compton suppression) have been evaluated for following ten elements: As, Au, Cd, Ga, K, La, Mo, Sb, Sm, and W. The results show that the method of 5-minute epithermal and a 1-day decay is the optimum way to analyze Ga, while the addition of the Compton suppression is very beneficial for the determination of K. Using the Compton suppression system in conjunction with the 1-hour epithermal and a 1-week decay, is ideal to determine Au, Cd, Mo and W, while routine 1-hour thermal and a 1-week decay, is adequate to determine As, Sb, Sm and La in concentrations found in soil.     

INAA of geological materials using a combination of epithermal activation and Compton suppression: Prediction of possibilities

Nuclear data relevant to the determination of elements in geological materials by instrumental neutron activation analysis using a combination of epithermal neutron activation and Compton suppression counting are presented. The feasibility of this combination is discussed considering data for desired as well as interfering nuclides. Among elements determined after short irradiation, the conditions for Sr, Zr, I, Cs, Eu and U should be improved. After long epithermal irradiation and appropriate decay, Compton suppression should lead to improvement in determination of As, Rb, Sr, Mo, Sn, Sb, Ba, Gd, Ho, Tm, W, Au, Th, and U. In the case of Ga, Se, Ag, In, Cs, Tb, Yb, Hf, Ta, and W, the use of Compton suppression in connection with epithermal activation is not recommended because the radionuclides concerned decay with coincident γ-rays. In general, the use of Compton suppression should improve the determination of trace elements in geological materials by epithermal neutron activation analysis, but more work is needed to better quantify these improvements.     

Improvement of analytical sensitivities for the determination of antimony,arsenic, cadmium,indium, iodine,molybdenum, silicon and uranium in airborne particulate matter by epithermal neutron activation analysis

As part of an ongoing Great Lakes deposition study, we have determined a series of heavy metals in air filter samples collected near Lake Ontario. To decrease our detection limits for key elements used in our receptor modeling, we have employed instrumental epithermal neutron activation analysis (NAA) and Compton suppression techniques. Our detection limits were much better than those with thermal NAA, typically, 0.3 ng for Sb, 0.7 ng for As, 8 ng for Cd, 0.2 ng for In, 14 ng for I, 5 ng for Mo and 2 ng for U. Silicon, which is usually not reported in conventional NAA results for air filters, was routinely determined at the 60 g level. Accuracy was corroborated by analyzing the certified reference material concurrently.     

A comprehensive study for the determination of forty eight elements in the certification of a hazardous standard reference material

The centification of standard reference materials is of fundamental importance for environmental scientists to proceed with their own quality control programs or calibration procedures. As part of the National Institute of Standard and Technology (NIST) program, we participated in the certification of a hazardous waste material. Our efforts concentrated on judiciously using thermal and epithermal neutron activation analysis in conjunction with Compton suppression techniques. We have demonstrated that besides lowering the detection limit for several elements usually not reported by conventional NAA, Compton suppression is ideally suited to substantially reduce certain spectrla interferences. A detailed comprehensive study was undertaken using this method to highlight which isotopes can be most favorably used.     

William D. Ehmann, radioanalytical chemist and radiochemistry educator

Copper (Cu) is an essential element and is incorporated in many biomolecules that are involved in protecting the brain from oxidative damage. Many brain regions strongly affected by neurodegene rative diseases are small. A sensitive nondestructive procedure to determine Cu is desirable to preserve samples for additional studies. Copper is not easily determined by instrumental neutron activation analysis (INAA) due to high activity levels produced by major abundance elements such as sodium (Na) and chlorine (Cl), which produce a high Compton background. An INAA method involving a short epithermal neutron irradiation and counting with a Compton suppression system was developed to determine Cu in brain, via 5.1-min⁶⁶Cu. These short irradiation results are compared to those based on coincidence spectrometry of annihilation photons from positron emitting 12.7-h⁶⁴Cu after a long irradiation.     

Characterization of household plastics for heavy metals using neutron activation analysis

Highly enriched concentrations of several heavy metals have been found in municipal solid waste incinerator (MSWI) ash. In an effort to identify possible sources of these metals in MSWI ash, a variety of disposable household plastic products was examined for heavy metal content. Using both thermal and epithermal neutron activation analysis (NAA) along with Compton suppression techniques, concentrations of several trace and heavy metals including Ag, As, Au, Ba, Br, Cd, Cr, Cu, Fe, Mn, Ni, Sb, Se, Sn, Sr, V, W and Zn were determined. Results indicate a wide range of concentrations for these elements, with large variations in plastics of similar color and intended use. As limits dealing with heavy metal content of consumer products are lowered, NAA techniques will provide a useful method for verification of product compliance.     

Evaluation of atmospheric airborne particles in Lisbon, Portugal using neutron activation analysis

Summary We have employed Compton supression neutron activation analysis in conjunction with thermal and epithermal neutrons to detemine trace elements in airborne particulate matter in Lisbon, Portugal. As a result of the proximity of ocean marine, elements such as sodium and chlorine can signficantly decrease the analytical sensitivities of many elements of interest due ot the high backgrounds arising from ³⁸Cl and ²⁴Na. Compton suppression has resulted in the increase of the analytical sensitivities using thermal neutrons of Al, Ba, Ce, Cr, Cu, Ni, Rb, Se, Th, Ti, V, and Zn. The use of Compton suppression and epithermal neutrons significantly reduced the detection limits for As, I, K, Si, and W, while the utilization of solely epithermal neutrons improved the analyses of In.     

Halogen determination in Arctic aerosols by neutron activation analysis with Compton suppression methods

The study of halogens particularly bromine and chlorine in Arctic aerosolshas received a great deal of attention in the past decade in ozone depletionduring polar sunrise studies. Iodine has also been studied as part of geochemicalcycling. We have shown that all three of the above elements can be determinedsimultaneously with very low detection limits using epithermal NAA in conjunctionwith Compton suppression methods. Besides lowering the background considerably,Compton suppression can eliminate or minimize the overlapping peak of the620 keV photopeak arising form the 1642 keV double escape peak of ³⁸Cl interfering with the 616.9 keV photopeak of ⁷⁹Br(n,) ⁸⁰ Br reaction. Iodine is ideally determined by epithermal NAAbecause of its very good resonance integral cross-section. Although chlorineis usually determined using thermal neutrons via the ³⁷Cl(n,) ³⁸Cl reactions, epithermal NAA is still feasible for the Arcticaerosol, since it has a major sea-salt component.     

Removal of sodium and chlorine from seawater prior to neutron activation analysis for trace elements

A neutron activation analysis (NAA) method has been developed for the determination of 14 elements in seawater samples. The method consists of pre-irradiation separations of interfering elements, viz. Na with hydrated antimony pentoxide, leached Sb using either acid aluminum oxide or tin dioxide, and Cl and Br with a mixture of nitric acid and hydrogen peroxide, followed by 3 different irradiation, decay and counting periods. Concentrations of Ag, Co, Cr, Cu, Fe, La, Lu, Mn, Mo, Sc, Sm, Ti, V and Zn have been measured and compared with those obtained by an independent preconcentration method. Precision and limits of detection and determination have been evaluated.     

Measuring activity of 235, 238U, 232Th and 40K in geological materials using neutron activation analysis

The radioactivity of the ^{235, 238}U and ²³²Th isotope decay chains for geological samples can usually be assumed to be in equilibrium due to their age. Similarly, one can assume that the isotopic mass proportions are equal to natural isotopic abundance. Current methods used to ascertain activity in these decay chains involve alpha particle spectrometry, ICP-MS or passive gamma-ray spectrometry, all of which can be laborious and time consuming. In this research, we have used thermal and epithermal neutron activation analysis (NAA) of small sample sizes of various geological materials in order to ascertain these activities. By using NAA, we aim to obviate cumbersome sample preparation, the need for large samples and extended counting time. In addition to the decay chains of uranium and thorium, ⁴⁰K was also determined using epithermal neutron activation analysis to determine total potassium content and then subtracting out its isotopic contribution.     

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.     

Compton suppression neutron activation analysis: Past,present and future

Conclusions In this work a review of the development of compton suppression is presented. It was shown that the application of Compton-suppression counting in instrumental NAA reduces the detection limits and improves the accuracy for a list of elements by substantial reduction of the background of the -spectroscopy. Results for certified reference materials obtained through the use of Compton suppression are normally more accurate and in agreement with the published values. Compton suppression is particularly helpful for low level concentrations in environmental samples to those elements which exhibit severe special interferences in the normal NAA counting. A list of the elements with isotopes having single or close to single -ray decay schemes and which could benefit from Compton-suppression counting is presented. Also, evaluation is made regarding the reliability of Compton suppression with increase in the overall dead-time of the counting. It was concluded that this method does not provide accurate quantification of the isotopes when the overall dead-time exceeds the 10% range. Investigation of the natural background was performed with Compton suppression for the purpose of neutron activation analysis application. The method presented proves to broaden the application of NAA and helps in its competition for simplicity, accuracy and reliability with the modern methods of elemental analysis. Future application of coincidence spectrometry in activation analysis should include better enclosing of the primary detector, utiliza5tion of x-ray and well type detectors, -, -, and -- coincidence techniques.     

Study of PM2.5 in Beijing suburban site by neutron activation analysis and source apportionment

Airborne particulate matter (APM) was collected in coarse fraction and in PM_2.5 during spring of 2002 in Beijing suburban sampling site by Gent SFU sampler. More attention has been paid to the special “events” such as dust, storm and haze. Taking advantage of the combination of thermal or epithermal neutron irradiation with Compton suppression spectrometer system, twenty elemental (Al, Si, Ca, K, Dy, Cu, I, In, Ba, W, Sn, Sb, As, Ti, Br, V, Mn, Cl, Na, Zn) concentration were determined. Among them, several key trace elements that cannot be accomplished by the traditional neutron activation analysis (NAA) were determined. The analysis of trace elemental concentration in PM_2.5 shows that the anthropogenic elements such as As, In, Sn, Sb have different trends than crustal elements. The back-trajectories of the high concentration anthropogenic pollution elements revealed their source region. Six potential sources were resolved by positive matrix factorization (PMF), two area type and four source type, as soil, limestone quarry, crop burning and mixture of residue motor and coal burning sampling sites. Taking into account of everyday air particle back trajectories, source compositions together with source regions were also identified. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Epithermal neutron activation analysis and its application in the Miniature Neutron Source Reactor

The cadmium and boron ratios from 44 elements, totally 66 nuclides, were determined in the inner and outer irradiation sites of the Miniature Neutron Source Reactor (MNSR). China Institute of Atomic Energy. A permanent Cd-shielded epithermal neutron irradiation site has been designed and installed in the outer of the beryllium reflector of this reactor. Elements e.g., I, Br, Sr, Si, Th and U in biological samples, such as foodstuff, water and blood, geological and environmental samples, such as soil, rock, sediment and vegetable leaves were analyzed by BN-shielded epithermal neutron activation analysis (ENAA), and Au, As, Sb, Th and U by Cd-shielded ENAA. The results show that the detection limits of these elements by ENAA are better by a factor of 1.5–7 than those with conventional NAA.     

Performance of Compton suppression system (CSS) and applicability in food matrices

As a non-destructive and multi-element technique, with high-level metrological properties, instrumental neutron activation analysis (INAA) has an important role to determine chemical elements in food. However, its use may be limited when looking for mass fractions near the detection limits. The Compton scattering of higher energy gamma-rays raised the spectrum baseline thus impairing the determination of several elements. Therefore, the gamma-ray spectrometry with Compton suppression becomes an alternative for improving the performance of INAA, since it can reduce the uncertainty of measurements and the detection limits by increasing the proportion between photopeak area and baseline. Here the performance of a Compton suppression system set by Ortec, with 50% relative efficiency and 2.04?keV resolution (FWHM) for the 1,332?keV photopeak, was evaluated for food analysis. Samples of beans, chickpeas, lentils, peas, and rice were irradiated with neutrons and measured in the suppression system. Detection limits calculated from suppressed and unsuppressed spectra were compared. The suppression factor achieved by the system for ¹³⁷Cs was 5.88?±?0.11 (n?=?20) in the plateau region (358 to 382?keV), which was stable along a 20?week period and similar to the data provided in literature for other systems. Amongst fifteen elements determined, the detection limits for Br, Co, La, Na, Sc, and Se were not improved by the use of Compton suppression. On the other hand, the variable improvement obtained for As, Ca, Cd, Cr, Fe, Hg, K, Rb, and Zn corroborated the idea that the performance of the Compton suppressor must be individually assessed for each type of sample.     

Extending NAA to materials with high concentrations of neutron absorbing elements

Summary The recently discovered universal functions for thermal and epithermal neutron self-shielding were adapted to NAA of cylindrical samples, expressing the magnitude as the product of a nuclear factor, a geometrical factor and the amount of the neutron absorbing element. The theory was tested and the nuclear factors were measured for 1 ml samples containing the halogens Cl, Br and I. Tests on samples containing these elements at a priori unknown concentrations, irradiated in a mixed thermal and epithermal neutron spectrum, showed that self-shielding as high as 30% could be corrected with an accuracy of about 1%, except in cases with significant epithermal shielding of one element by another.     

Concentrations of trace and major elements in Mission–Progresso (Texas) soils

Neutron Activation Analysis (NAA) was applied to determine trace and major elements in Mission–Progresso (Texas) soils. The Rio Grande river runs along the USA—Mexico border. The soil samples were collected at Mission and Progresso areas of the Rio Grande riverbank in the USA side. Soils were analyzed for the presence of toxic effluents due to human activities that might affect agricultural products and health because one of the possible paths of intoxication is the agricultural product consumption. Dried, sieved, and blended soil samples (~1.5 g) were irradiated at the UT Austin TRIGA reactor at a thermal neutron flux of 1 × 10¹² n cm⁻²s⁻¹ and epithermal neutron flux of 1 × 10¹¹ n cm⁻²s⁻¹. Different irradiations, decay, and counting times were combined to determine concentration and detection limits of 21 elements which represent four areas in Mission–Progresso (Texas) with the aim to achieve a consistent characterization. NIST certified reference materials were used in relative analysis and also to determine the accuracy and reproducibility values. The neutron flux was monitored using sulfur flux monitor wires. Normal and Compton suppression gamma ray spectrometers were used to detect different gamma ray energy peaks and this Compton system greatly reduces the background. Concentrations are evaluated in per cent and parts per million and errors are within acceptable levels and these values are compared with values reported in literatures from other countries. The results do not show significant contaminations neither from the Rio Grande river nor from nearby industries.