Determination of Th and U at ppt levels in a neutral hot spring water by neutron activation analysis

Neutron activation analysis was successfully applied to the determination of Th and U at ppt levels in a neutral hot spring water. Blank test corrections were found to be essential to reach the final determined values. Normal NAA is a better method for the Th determination than epithermal NAA, while both NAAs are nearly equally effective for U determination.     

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.     

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.     

Determination of rare earth elements in hot spring and crater lake waters by epithermal neutron activation analysis

Determination of the rare earth elements (REE's) in acidic hot spring and crater lake waters by neutron activation analysis (NAA), in which activation was performed mostly by epithermal neutrons (epithermal NAA) was investigated. Nine REE's, La, Ce, Sm, Eu, Tb, Ho, Tm, Yb and Lu, out of fourteen naturally existing REE's were determined at ppb levels with satisfactory precision. The epithermal NAA was found to be more effective in the determination of Sm, Tb, Ho and Yb than normal NAA, in which activation was performed mainly by thermal neutrons. Combined use of the epithermal and normal NAA's enabled the determination of eleven REE's, La, Ce, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb and Lu.     

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 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.     

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.     

Determination of concentrations of U and Th in their mixed oxides by INAA methods

Uranium and thorium mixed oxides are being prepared using natural U and Th for studies on fuels for Advanced Heavy Water Reactors, wherein composition of U and Th is specific and requires strict control in terms their contents and homogeneity. Chemical quality control necessitates accurate and precise compositional characterization of the fuel material by a suitable analytical method. Among various analytical methods for U and Th, instrumental neutron activation analysis (INAA) is one of the best methods for their simultaneous determination without chemical dissolution and separation. INAA methods using reactor neutrons namely thermal NAA and epithermal NAA were standardized for the determination of U and Th in their mixed oxides. Standards, synthetic samples and U–Th mixed oxide samples, prepared in cellulose matrix, were irradiated at pneumatic carrier facility of Dhruva reactor as well as at self serve facility of CIRUS reactor under cadmium cover (0.5 mm). Radioactive assay was carried out using a 40% relative efficiency HPGe detector. Both activation and daughter products of ²³⁸U (²³⁹U and ²³⁹Np) and ²³²Th (²³³Th and ²³³Pa) were used for their concentration determination. The method was validated by analyzing synthetic samples of 6–48%U–Th mixed oxides. The standardized method was used for the concentration determination of U and Th in 4–30%U–Th mixed oxide samples. Results of U and Th concentrations including associated uncertainties obtained from the INAA methods are presented in this paper.     

Determination of cobalt in nickel in the sub-ppm level with cold neutrons

The determination of cobalt in nickel with neutron activation analysis (NAA) is hindered by an interfering nuclear reaction induced by fast neutrons. To overcome this obstacle cold neutron beam irradiation has been carried out. As a result, a cobalt concentration of 0.25±0.02 μg/g in nickel foil has been determined. This nickel foil is intended to become a reference material for neutron dosimetry.     

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.     

Determination of Ga,Th, and U in Bauxite and Coal Ash by Epithermal Neutron Activation Analysis

Neutron activation analysis is applied to the determination of Ga, Th and U in Bauxite and coal ash; thermal and epithermal irradiations are used. The other analytical methods are also quantitatively surveyed for gallium. The results indicate that epithermal neutron activation is prefered for those trace elements because the former method is more simple and quick.     

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.     

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.     

Instrumental NAA of carbonate rocks and its application for the analysis of secondary sedimentary environments in shallow sea

Aiming at distinguishing between the sedimentary environments in shallow sea using elemental geochemical markers, the determinations of trace elements in carbonate rocks by thermal neutron, epithermal neutron and short-irradiation activation analysis have been studied, and more than 30 major and trace elements determined. Al, Cl, Sc, Ti, V, Cr, Fe, Co, As, Br, Rb, Sb, Cs, Lu, Hf, Ta, Th and U were found to be the effective distinguishing markers for the secondary environments in shallow sea.     

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.     

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.     

Uranium and thorium analyses by delayed fission neutron counting technique using a small neutron generator

Applicability of a small neutron generator and a dual rectangular tube sample transfer system for analyses of U and Th using delayed fission neutron technique has been investigated. A way of optimizing the timing parameters is reported. At a fast neutron flux of 10⁸ n.cm^–2s^–1, 0.02 w% U can be determined. For thorium determination this method is less sensitive. The Cd difference technique can be used for the simultaneous determination of U and Th but it has lower sensitivity.This work was supported in part by the IAEA.     

Determination of trace metals by neutron activation after coprecipitation with lead phosphate

Lead phosphate quantitatively coprecipitates trace amounts of Ag(I), Cd(II), Cr(III), Cu(II), Mn(II), Th(IV), U(VI) and Zr(IV). The trace elements are determined in the precipitate by instrumental neutron activation analysis (INAA); detection limits are given. The practical application to the determination of U and Th is described.     

Determination of cadmium in soils by neutron-activation analysis

A radiochemical neutron-activation method for the determination of cadmium in soils is presented. The irradiation is carried out in a neutron flux with a high epithermal component, taking advantage of the high ratio of the resonance-activation integral to the thermal-neutron cross-section for (114)Cd to obtain an increased sensitivity. The irradiated samples are decomposed with hydrofluoric acid-nitric acid and cadmium is separated by anion-exchange. Zinc may also be determined. There is good agreement with results obtained by atomic-absorption spectrophotometry based on solvent extraction separation of cadmium.