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.     

Determination of zinc in geological samples using Compton suppression with thermal and epithermal instrumental neutron activation analysis

The determination of Zn in geological samples using instrumental neutron activation analysis is usually done using the ⁶⁴Zn(n,γ)⁶⁵Zn reaction and its 244 day half-life. However this analysis has proven to be potentially difficult. This is due to its relatively low neutron absorption cross section and gamma ray intensity, and the relatively high neutron absorption cross section and gamma intensity of ⁴⁶Sc, which has an energy peak that is only 5 keV greater than ⁶⁵Zn. The use of a high resolution detector makes it possible to differentiate between the ⁶⁵Zn and ⁴⁶Sc photopeaks peaks. However, the dominating ⁴⁶Sc gamma ray can even make peak fitting routines unsuccessful in the proper determination of ⁶⁵Zn. The use of a Compton suppression system suppresses the ⁴⁶Sc peak, which has two coincident gamma-rays, and this greatly improves the ratio of the height of the ⁴⁶Sc 1120.5 keV photopeak to the ⁶⁵Zn 1115.4 keV photopeak. Irradiating the sample with epithermal neutrons also improves the measurement since ⁶⁵Zn has a higher cross section for epithermal neutrons rather than thermal neutrons, whereas ⁴⁶Sc has a higher thermal cross section. Another technique to determine zinc is the use of ⁶⁸Zn(n,γ)^69mZn reaction with its 13 h half-life using epithermal neutrons and Compton suppression INAA. However, the 438 keV gamma ray of ^69mZn has no interference with any adjoining photopeak. A critical comparison of these two methods is given.     

Improved detection limits for trace elements on aerosol filters using Compton suppression counting and epithermal irradiation techniques

Aerosol samples were collected on Whatman 41 filters at two sites near Lake Huron and one site near Lake Ontario. These samples were then analyzed by instrumental neutron activation analysis (NAA) at the University of Illinois. The detection limits for certain trace elements were enhanced by irradiation with both thermal and epithermal neutrons and also by counting with Compton suppression techniques. The sample was divided in half to allow for four irradiations. Short-lived thermal NAA resulted in the determination of Al, Br, Ca, Cl, Cu, K, Mn, Na, Ti, and V. A short epithermal irradiation was used to determine Cu, I, In, Si, Sn and U. A one and one-half hour epithermal irradiation was utilized for the determination of As, Au, Br, Sm, Sb, and W. The elements Cr, Cs, Fe, Hf, Ni, Sc, Se, Th. Zn, and several rare earths were determined with a long thermal irradiation. Utilizing a Compton suppression gamma-ray counting system reduced the background and enhanced the detection of several isotopes which primarily emit only a single gamma-ray upon decay. Counting was simultaneously performed with a normal counting mode so that the detection of isotopes with multiple decay gamma-rays was not impaired.     

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.     

Determination of macroconstituents and trace elements in naturally occurring radioactive material in oil exploration waste products

Naturally occurring radioactive materials (NORM) contain radionuclides, such as radium, thorium, and uranium. The existence of NORM remains an issue for oil and gas exploration because once the material becomes concentrated through technological activity, it becomes a radioactive contamination hazard or a radioactive waste. Pipes and tanks used to handle large volumes of produced water at some oil-field sites are coated with scale deposits that contain high levels ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb. Experiments were conducted using thermal and epithermal neutron activation analysis and Compton suppression for the determination of macroconstituents and trace elements in the radioactive scale sample.     

Non-destructive determination of trace amounts of iodine in biological samples by epithermal neutron activation and Compton suppression gamma-ray spectrometry

In order to investigate the ingestion of iodine by human body and to know its content in organs, instrumental epithermal neutron activation analysis was used in conjunction with Compton suppression gamma-ray spectrometry by measuring the ¹²⁸I short-lived nuclide. The interferences of ²⁴Na and ³⁸Cl induced from NaCl in a sample were reduced by factors of about 6 and 15 to 41 by employing the epithermal neutron activation and Compton suppression gamma-ray spectrometry, respectively. The present method can be used to determine iodine at levels higher than 11 ppb. It was applied to the determination of iodine of more than 35 ppb in various biological reference materials.     

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.     

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.     

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.     

Optimization of HANARO cold neutron induced prompt gamma activation analysis system by using Monte Carlo code

Prompt gamma activation analysis (PGAA) is a nuclear analytical technique for non-destructive determination of elemental and isotopic compositions. The principle of PGAA technique is based on detection of captured gamma-ray emitted from an analytical sample while being irradiated with neutrons. Use of a cold neutron beam guide greatly reduces the gamma-ray background at the analytical sample while maintaining a neutron capture rate is comparable to that of standard thermal neutron PGAA. A new cold neutron induced prompt gamma activation analysis (CN-PGAA) system has been under construction since April of 2009 at the HANARO Cold Neutron Building (KAERI, Republic of KOREA). In this study, the Compton suppression factor of the CN-PGAA system was estimated to be 5.5 using a ⁶⁰Co radioactive source in conjunction with the MCNPX simulations. Several parameters of the CN-PGAA system were studied to estimate and optimize the performance of the system: scintillation material in the guarded detector of a Compton suppression spectrometer (CSS); the relative positions of the HPGe detector and annular detector; and the distance between the HPGe detector and back catcher BGO detectors of the CSS. In addition, the neutron ray-trace simulation package, McStas, was adopted to predict the neutron flux and wavelength distribution at the end of the cold neutron beam guide. These results served as input for the MCNPX simulation of the CN-PGAA system.     

Rapid analysis of biological reference materials by instrumental neutron activation

Summary Instrumental neutron activation analysis (INAA) was applied to the rapid determination of cadmium and other elements in the IAEA biological reference material horse-kidney (H-8). Nuclear reactor neutrons and epithermal neutrons were used as neutron sources. Cadmium, bromide, iodine and phosphorus were determined by epithermal neutron activation analysis. Aluminum was determined by reactor neutron activation analysis taking into account the contribution of phosphorus to the ²⁸Al activity.     

Determination of selected elements in bone samples by neutron activation and γ-spectrometry

A non-destructive method for the quantification of eleven elements in bone samples is described. The analytical scheme is based on short (30 s) irradiation with thermal neutrons followed immediately (decay time 10 s) by counting fluorine-20 for 30 s and, after a total waiting time of 150 s, by 10-min γ-spectrometry counting, which give data for Ca, Cl, Mg, Mn, Na, and V. Use of a boron carbide shield for a second set of irradiations with epithermal neutrons permits the additional determination of bromine and strontium and calculation of the contribution of aluminium and phosphorus to the total activity of ₂₈Al.     

Fast neutron activation analysis of silicon in aluminum alloys

The silicon content in an aluminum-silicon alloy was measured by nondestructive fast neutron activation analysis with fission spectrum neutrons. A boron nitride irradiation container reduced the flux of thermal and epithermal neutrons at the sample position, enhancing the²⁹Si (n, p)²⁹Al reaction. A detection limit of 0.4% silicon in a 0.5 g alloy sample was obtained.     

Trace analysis and leaching dynamics of volcanic ash using NAA and ICP-MS

In 2010, Mt Merapi in Indonesia erupted releasing approximately 160 million tonnes of ash, roughly 75 % of which fell on or near Indonesia. With this extreme amount of a substance, even tract elements can become relevant. We have identified a variety of trace and major elements in this ash using instrumental neutron activation analysis. We have used a variety of techniques to improve our measurements, such as the use of epithermal neutrons and a Compton suppression system that resulted in accurate measurements of a wide range of trace elements including heavy metals. In order to better understand the leaching dynamics at which various elements can enter the local waters and have either enriching or toxic effects on the local ecosystem, we used a modified US Environmental Protection Agency Toxicity Characterization Leaching Procedure (TCLP) employing simulated rainwater.     

Intercomparison and determination of environmental standard samples by instrumental neutron activation analysis

To identify and improve the analytical technique for air pollution research, four kinds of environmental standard samples, i.e., airbome particulate matter, coal flyash, soil and pine needle supplied from the NIST and the IAEA were analyzed using thermal and epithermal neutron activation techniques. Sample irradiation was done at the irradiation facilities (neutron flux, 1 · 10¹³ n·cm^–2·s^–1) of the TRIGA MARK-III Research Reactor in the Korea Atomic Energy Research Institute. The accuracy and precision for the analysis of 40 trace and toxic elements in the samples were compared with the certified and reported values, respectively. In the analytical results of all standard reference materials, the relative standard deviation were within the 15% except for 11 elements and the relative error were agreed within the 10–20% except for 13 elements. The benefit of epithermal activation was investigated and the optimum analytical condition is reported.     

Determination of bromine, chlorine and iodine in environmental aqueous samples by epithermal neutron activation analysis and Compton suppression

Summary Halides, particularly Br^- and Cl^-, have been used as indicators of potential sources of Na⁺ and Cl^- in surface water and groundwater with limited success. Contamination of groundwater and surface water by Na⁺ and Cl^- is a common occurrence in growing urban areas and adversely affects municipal and private water supplies in Illinois and other states, as well as vegetation in environmentally sensitive areas. Neutron activation analysis (NAA) can be effectively used to determine these halogens, but often the elevated concentrations of sodium and chlorine in water samples can give rise to very high detection limits for bromine and iodine due to elevated backgrounds from the activation process. We present a detailed analytical scheme to determine Cl, Br and I in aqueous samples with widely varying Na and Cl concentrations using epithermal NAA in conjunction with Compton suppression.     

Evidence of tin and other anthropogenic metals in particulate matter in Lisbon, Portugal

Thermal and epithermal neutron activation analysis techniques were used to analyze 27 Teflon air filters which were exposed to ambient air in Lisbon, Portugal, in February 2007. Tin was detected which is strongly suggestive of an anthropogenic source. Arsenic, antimony and copper were shown to be highly correlated, which is also suggestive of anthropogenic pollution. Trace element analysis of short- and medium-lived isotopes was performed yielding concentration information of various elements. Analytical sensitivities were enhanced using a Compton suppression system. Enrichment factor analysis shows that arsenic, tin, zinc, copper and antimony are at elevated concentrations in the Lisbon atmosphere.     

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.