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.     

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.     

Instrumental activation analysis of coal and fly ash with thermal and epithermal neutrons and short-lived nuclides

Instrumental neutron activation analysis is applied to the determination of about 25 elements in coals and fly ash by means of nuclides with half-lives of less than 48 h ; thermal and epithermal irradiations are used. The results indicate that epithermal activation is preferable for twelve of the elements (Ga, As, Br, Sr, In, Cs, Ba, La, Sm, Ho, W and U). Data for SRM 1632 (coal) and SRM 1633 (fly ash) compare favorably with the results obtained by other investigators.     

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.     

Instrumental activation analysis of coal and fly ash with thermal and epithermal neutrons

A systematic comparison of thermal and epithermal irradiations in the instrumental activation analysis of coal and fly ash was made. From a total of 44 elements, the epithermal irradiation technique appeared advantageous in 20 cases, namely Ni, Ga, As, Se, Br, Rb, Sr, Zr, Mo, In, Sb, Cs, Ba, Sm, Ho, Hf, Ta, W, Th and U. Data are presented for the National Bureau of Standards’ coal (SRM 1632) and fly ash (SRM 1633).     

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.     

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.     

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.     

Daily dietary intake of elements of nutritional and radiological importance by adult Koreans

A one day representative mixed diet of an adult Korean was collectedfrom the data based on the food intake of 108 healthy subjects between theages 20 and 50. Sampling for the Korean total diet was carried out by usinga market basket study based on the Korean standard food consumption schemereported by the Korean Nutrition Society. Average consumption frequency ofdifferent food items for a one day representative mixed diet of an adult Koreanand the amount of each item to prepare a one day Korean representative totaldiet are surveyed. The analytical methods involve both instrumental and radiochemicalneutron activation techniques developed for the determination of the elementsCs, I, Sr, Th and U in various kinds of food samples. Concentrations of traceelements including 5 important elements for radiological protection, U, Th,Cs, Sr and I in the Korean total diet and the 4 most frequently consumed Koreanfoodstuffs have been analyzed by neutron activation analysis. Detection limitsfor U, Th, Sr and I were improved to ppb levels by radiochemical separationafter neutron irradiation. Five biological NIST reference materials were alsoanalyzed for quality control of the analysis. Seventeen trace elements inthe Korean total diet and four Korean representative foodstuffs were alsoanalyzed quantitatively by instrumental neutron activation analysis.     

Choice of boron shield in epithermal neutron activation determinations

Boron trioxide, boron nitride, boron carbide and elemental boron giving different boron surface densities have been used as neutron shields in epithermal neutron activation determinations. Boron ratios and advantage factors for 29 nuclides have been determined. A new expression of the advantage factor has been derived from statistics of radioactive decay viewpoint. A real improvement, in comparison with classical neutron activation methods, can be obtained for the determination of As, Br, Cd, I, Mo. Sb, Sn, Th, W and U by use of boron shields.     

Intercomparison of moss reference material by different multi-element techniques

An intercomparison of data obtained for a moss reference material (Hylocomium splendens) used as biomonitor of atmospheric deposition by different multi-element techniques is presented. In total 43 elements (Na, Mg, Al, Cl, K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Zr, Ag, Sn, Sb, I, Cs, Ba, La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb, Lu, Hf, Ta, W, Au, Th, U) were determined using inductively coupled plasma-mass spectrometry (ICP-MS), conventional instrumental neutron activation analysis (INAA), epithermal neutron activation analysis (ENAA) and as well as shorttime neutron activation analysis without and with a⁶LiD-converter. Advantages and drawbacks of each method are discussed. The introduction of moss reference materials for atmospheric multi-element deposition studies involving nuclear analytical techniques is strongly recommended.     

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.     

Accelerated denitration by formic acid accompanied with residual acid-electrolytic trimming

The fruit bodies of wild-growing higher fungi (macromycetes), commonly called mushrooms, of various genera and species collected in localities with different geochemical features and man-made burden in the Czech Republic were analyzed by different modes of activation analysis. The elements Na, Mg, Al, S, Cl, K, Ti, V, Mn, Cu, Br, Ba and Dy were determined by short-term instrumental neutron activation analysis (INAA). Short-term epithermal INAA (ENAA) was used for determination of I and other elements, such as Rb, Ag, and U. The elements Na, K, Sc, Cr, Fe, Co, Cu, Zn, As, Se, Br, Rb, Ag, Cd, Sb, Cs, Ba, La, Ce, Sm, Eu, Hf, Au, Hg and Th were determined by long-term INAA, whereas long-term ENAA enabled determination of several other elements, such as Ni, Ta, W and U. The analytical possibilities of instrumental photon activation analysis (IPAA) using a microtron were also explored and found useful for determination of several additional elements, namely Sr, Y, Zr, Nb, and Pb. High concentrations of several essential and toxic trace elements found (up to hundreds of mg^.g^-1, dry mass) should be of concern in nutritional studies, because mushrooms form non-negligible part of diet in many countries, especially in Middle and East Europe.     

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.     

Determination of 30 elements in coal and fly ash by thermal and epithermal neutron-activation analysis

Thirty elements are determined in coal and fly ash by instrumental neutron-activation analysis using both thermal and epithermal irradiation. Gamma-ray spectra were recorded 7 and 20 days after the irradiations. The procedure is applicable to the routine analysis of coals and fly ash. Epithermal irradiation was found preferable for the determination of Ni, Zn, As, Se, Br, Rb, Sr, Mo, Sb, Cs, Ba, Sm, Tb, Hf, Ta, W, Th and U, whereas thermal irradiation was best for Sc, Cr, Fe, Co, La, Ce, Nd, Eu, Yb and Lu. Results for SRM 1632 (coal) and SRM 1633 (fly ash) agree with those of other investigators.     

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.     

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.     

Investigation of gamma-spectra of biological materials irradiated in the epithermal range of the reactor neutron spectrum

Irradiation of various biological materials in the nuclear reactor neutron epithermal flux allows the increase of the selectivity of the pure instrumental method of activation analysis for the definite set of tracers either not determined instrumentally during sample irradiation by the thermal neutron flux or determined with low sensitivity. The given paper describes a method of increasing the sensitivity of the instrumental neutron activation determination of As, Br, Mo, Cd, Sb, W and Au in biological materials at the level of the whole blood, tissue and subcellular components.     

Improved ease of operation in epithermal NAA by irradiation in plastic capsules and use of well-type Ge-spectrometry: A feasibility study

An epithermal neutron activation analysis (ENAA) procedure has been evaluated in which samples packed in polyethylene capsules are irradiated during 15 minutes only, and induced activities are counted using well-type Ge-spectrometry. The evaluation was carried out in order to improve on ease of operation in ENAA. Biological and sediment reference materials have been analyzed. Compared to routine INAA, an improvement in detection limits was observed for As, Au, Cd, Mo, Ni, Sb, Sm, Sr, Ta, U, W and Zn. By Au–Zr neutron flux monitors, epithermal flux gradients have been determined. Concentrations found in the reference materials were generally in agreement with certified and consensus values.