Evolution of 40K in fruit collected in Malaysia by the determination of total potassium using neutron activation analysis

Potassium is an extremely important major to element to the human body. Potassium in made up of three isotopes with abundances of ³⁹K at 93.1%, ⁴⁰K at 0.0118% and ⁴¹K at 6.88%. It is also very well known that ⁴⁰K is to measure the single 1460.8 keV photon from beta-decay. However, this procedure requires a significant amount of sample and typical counting periods of at least a day in well-shielded germanium counting system. Another approach is to determination total potassium via neutron activation analysis using the well know ⁴¹K (n,γ) ⁴²K(T _1/2 = 12.8 h) reaction and then evaluate ⁴⁰K using the usual activity equation A = λN. In our laboratory we have effectively used thermal and epithermal neutron flux for neutron activation analysis to determine potassium in fruits. Upward to 7–9 batches of samples, which each of batch is including 14 samples so can be analysed in 1 day using only gram quantities of material. In such way on can increase the output of determining ⁴⁰K by at least on order of magnitude. Result of a detailed investigation optimization of the methodology, quality control and detection limits will be presented for reference material and various fruits samples.     

Dating of mineral samples through activation analysis of argon

Mass Spectrometry has been the usual method to determine Ar concentrations in mineral samples for dating them through the⁴⁰Ar/⁴⁰K ratio. This technique has been replaced since 1966 by measurement of⁴⁰Ar/³⁹Ar ratio, after artificial production of³⁹Ar from the³⁹K(n,p)³⁹Ar reaction produced in the fast neutron flux of a nuclear reactor. This method requires the fusion of the sample by incremental heating until reaching a temperature of 1000°C in order to get the total release of both argon isotopes. In principle, it should be possible to determine the⁴⁰Ar/⁴⁰K ratio by activation analysis in an easier, non-destructive way, but it presents the following drawbacks: manufacture of argon standards; usual low ratio peak/Compton distribution for both peaks: 1.29 Mev and 1.52 Mev (⁴¹Ar and⁴²K respectively), since potassium minerals are usually very rich in sodium, manganese and chlorine; reaction⁴¹K(n,p)⁴¹Ar induced by fast neutrons present in the thermal flux; and possible contamination of the samples and standards with atmospheric⁴⁰Ar (99.6% of elementary Ar, whose proportion in the atmosphere at sea level is 0.93%). This paper describes how these problems may be solved, also determining the limits of Ar and K concentration related to Compton distribution, in our experimental conditions.     

Liquid scintillation measurement of40K for the education on radioactivity

Liquid scintillation counting of⁴⁰K in ordinary potassium propionate is a highly suitable experimental task in the general education on radioactivity. The counting efficiency is about 90%, depending little on the measurement conditions. Potassium propionate is of suitable properties and can be easily obtained commercially or by conversion from other compounds. The result of counting, about 1,700 cpm/g, is highly impressive to many students, indicating the existence of⁴⁰K radioactivity unexpectedly high in the normal nature, and can be used for the exercise of calculating our internal radiation exposure.     

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.     

Utilization of42Ar−42K generator for isotope dilution analysis of potassium in ultra-pure water

Carrier- and salt-free⁴²K milked from an⁴²Ar–⁴²K generator was utilized for isotope dilution analysis of potassium in ultra-pure water. Potassium in the sample marked with the⁴²K was shown to be concentrated easily 60 times by crown-ether extraction and acid back-extraction to be determined by atomic absorption spectrophotometry. The same extractions proved to be effective for removing the reagent blank. Cerenkov radiation counting was often suitable for⁴²K measurement. The⁴²K was used also for studying the interaction of ultra-low concentrations of potassium with vessel walls.     

<Superscript>40</Superscript>K activities and potassium concentrations in tobacco samples of Mexican cigarettes

Nine brands of tobacco cigarettes manufactured and distributed in the Mexican market were analyzed by γ-spectrometry to certify their non-artificial radioactive contamination. Since natural occurring radioactive materials (NORM) ⁴⁰K, ²³²Th, ²³⁵U, and ²³⁹U (and decay products from the latter three nuclides) are the main sources for human radiation exposure, the aim of this work was to determine the activity of ⁴⁰K and potassium concentration. Averages of ⁴⁰K and potassium concentration were of 1.29±0.18 Bq·g⁻¹, and 4.0±0.57%. The annual dose equivalents to the whole body from ingestion and inhalation of 26 Bq ⁴⁰K were 0.23 μSv and 15.8 μSv, respectively. The corresponding 50 years committed dose equivalents was 0.23 μSv. The total committed dose to the lungs due to inhalation of ⁴⁰K in tobacco was 16 μSv. Potassium concentrations obtained in this work were in the same range of those obtained by INAA, so showing that the used technique is acute, reproducible, and accessible to laboratories equipped with low background scintillation detectors.     

A pilot study to measure levels of selected elements in Thai foods by instrumental neutron activation analysis

A pilot study was carried out to evaluate the scope of instrumental neutron activation analysis (INAA) for measuring the levels of selected elements in a few commonly consumed food items in Thailand. Several varieties of rice, beans, aquatic food items, vegetables and soybean products were bought from major distribution centers in Bangkok, Thailand. Samples were prepared according to the protocols prescribed by the nutritionist for food compositional analysis. Levels of As, Br, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, and Zn were measured by INAA using the irradiation and counting facilities available at the Thai Research Reactor with the maximum in-core thermal neutron flux of 3 × 10¹³ cm^?2 s^?1 of the Thailand Institute of Nuclear Technology in Bangkok. Selenium was determined by cyclic INAA using the Dalhousie University SLOWPOKE-2 Reactor facilities in Halifax, Canada at a thermal neutron flux of 2.5 × 10¹¹ cm^?2 s^?1. Both cooked and uncooked foods were analyzed. The elemental composition of food products was found to depend significantly on the raw material as well as the preparation technique.     

Rapid pretreatment of environmental samples of food and related materials by a microwave dehydration method

A rapid and simple radioactivity determination method has been developed for food and related environmental samples of a radioactivity level corresponding to 5 mrem/y, Japan AEC's guideline, by pretreating with a modified microwave dehydration apparatus followed by radiation counting. An equation to estimate the heating conditions by the apparatus has been derived, and results calculated by the equation are in good agreement with experimental data. It took less than 4.5 hours to dehydrate by the propossed method, and radiation counting could be started on the day of sampling and dehydration procedure. The lower limit of detection for each radionuclide by the proposed method, using a Ge(Li) detector of 20% relative efficiency, is lower than one half of the needed detection limit to determine and evaluate the 5 mrem/y level. Radionuclide levels in food samples such as vegetables and crustaceans were determined by the proposed method and it was found that they were below the lower dection limit of the proposed method except natural radionuclide⁴⁰K and fallout-originated¹³⁷Cs.     

Measuring magnesium,calcium and potassium isotope ratios using ICP-QMS with an octopole collision cell in tracer studies of nutrient uptake and translocation in plants

The ability of a quadrupole-based ICP-MS with an octopole collision cell to obtain precise and accurate measurements of isotope ratios of magnesium, calcium and potassium was evaluated. Hydrogen and helium were used as collision/reaction gases for ICP-MS isotope ratio measurements of calcium and potassium in order to avoid isobaric interference with the analyte ions from (mainly) argon ions ⁴⁰Ar⁺ and argon hydride ions ⁴⁰Ar¹H⁺. Mass discrimination factors determined for the isotope ratios ²⁵Mg/²⁴Mg, ⁴⁰Ca/⁴⁴Ca and ³⁹K/⁴¹K under optimized experimental conditions varied between 0.044 and 0.075. The measurement precisions for ²⁵Mg/²⁴Mg, ⁴⁰Ca/⁴⁴Ca and ³⁹K/⁴¹K were found to be 0.09%, 0.43% and 1.4%, respectively. This analytical method that uses ICP-QMS with a collision cell to obtain isotope ratio measurements of magnesium, calcium and potassium was used in routine mode to characterize biological samples (nutrient solution and small amounts of digested plant samples). The mass spectrometric technique was employed to study the dynamics of nutrient uptake and translocation in barley plants at different root temperatures (10 °C and 20 °C) using enriched stable isotopes (²⁵Mg, ⁴⁴Ca and ⁴¹K) as tracers. For instance, the mass spectrometric results of tracer experiments demonstrated enhanced ²⁵Mg and ⁴⁴Ca uptake and translocation into shoots at a root temperature of 20 °C 24 h after isotope spiking. In contrast, results obtained from ⁴¹K tracer experiments showed the highest ⁴¹K contents in plants spiked at a root temperature of 10 °C.     

Prompt gamma neutron activation analysis to measure whole body nitrogen absolutely: Its application to studies of in-vivo changes in body composition in health and disease

Whole body nitrogen has been measured absolutely in male volunteers and patients by in-vivo neutron activation analysis using whole body hydrogen as an internal standard. The 10.8 MeV and 2.2 MeV prompt gamma rays from nitrogen and hydrogen respectively give a result reproducible to 4% for a dose of 100 mRem. Whole body potassium measured by whole body counting natural⁴⁰K and whole body nitrogen have been correlated in normal adult males and patients. In the normals the correlation coefficient was 0.96 with coefficient of variation 4%. In the patients these parameters were 0.92 and 8% in 140 measurements. The ratio of N/K increased significantly as the degree of clinical wasting progressed.     

The Crystal Structure of Trimethyl Borate by Neutron and X‐ray Powder Diffraction

The crystal structure of one of the simplest organoboron compounds, trimethyl borate does not appear to have been determined hitherto. The compound is of interest for the study of π‐donor ligands and their interaction with the π‐acceptor behavior of trigonal boron and the consequences of such interactions on molecular structure. We used powder neutron (with isotopically labeled material) and X‐ray diffraction to determine the crystal structure of trimethyl borate at 15 K and 200 K (neutron) and 200 K (X‐ray). The material is hexagonal (Z = 2) with a = b = 6.950(8) Å and c = 6.501(3) Å at 15 K. The unit cell volume is 272.00(1) ų. The space group is P6₃/m (SG 176) at 15 K and 200 K. This is the first crystal structure solved on the Neutron Powder Diffractometer (NPDF) at the Lujan Center.     

Application of low background gamma-ray spectrometry to environmental monitoring samples: Water leaching treatment for 40K-removal

In the usual measurements of radionuclides in the environmental samples by g-ray spectrometry, Compton scattering of 1461 keV g-rays from ⁴⁰K severely interferes with the detection of artificial radionuclides in marine and agricultural products. In order to eliminate the interference of ⁴⁰K, we have developed a simple and convenient water leaching treatment method applicable to seaweed (sargasso) samples. By this treatment, over 98% of the potassium in seaweed samples is removed without notable losses of artificial and/or natural radionuclides. In combination with the low-level g-ray counting in the Ogoya underground laboratory, the detection limit could be improved by ~1 order of magnitude.     

Determination of <Superscript>228</Superscript>Ra in human bone ash containing significant quantities of <Superscript>40</Superscript>K and Ca<Superscript>2+</Superscript>

The determination of ²²⁸Ra by means of γ-spectrometry, in material containing significant quantities of ⁴⁰K and Ca²⁺ such as bone ash results in increased values of counting uncertainty and lower limit of detection (LLD) because of a significant contribution from the Compton continuum of ⁴⁰K. However, ⁴⁰K is widely removed from bone ash if ²²⁸Ra is coprecipitated with barium sulfate. As a result, the counting uncertainty and LLD are significantly reduced. A method is presented for determination of very low activity concentrations of ²²⁸Ra. Impurities introduced by precipitation are negligible when applying high resolution γ-spectrometry.     

The determination of tin in rocks by thermal neutron activation

A fast routine method for the determination of tin in rocks is discussed. The method is based on coprecipitation of tetravalent tin with ferric hydroxide, followed by a short irradiation in a high thermal neutron flux, extraction in toluene from 1∶1 sulphuric acid which is 5N in potassium iodide, and counting of^123mSn (T=40 m) or^125mSn (T=9.7 m) with a well-type NaI detector. In the present work^125mSn was used. The lower limit of determination is governed by the blank of the reagents. For a sample of at least one gram it is ≌ 0.2 μg Sn·g⁻¹.     

K3(Sc0.875Nb0.125)Nb2O9H1.75: a new scandium niobate with a unique cage structure

Potassium scandium niobate hydroxide, K₃(Sc_0.875Nb_0.125)Nb₂O₉H_1.75, is a new scandium niobate with a unique cage structure. The structure contains two non‐equivalent K⁺ sites (3m and m2 site symmetry), one disordered Sc³⁺/Nb⁵⁺ site (m site symmetry), one Nb⁵⁺ site (3m site symmetry), two O²⁻ sites (m and mm2 site symmetry) and one H⁺ site (m site symmetry). Both scandium and niobium have octahedral environments, which combine to form cages around potassium. One K atom lies in a cube‐like cage built of seven octahedra, while the other K atom is encapsulated by an eight‐membered trigonal face‐bicapped prism. The cages form sheets that extend along the ab plane.     

Studies on Nuclear Resonant Scattering of Synchrotron Radiation by 40K

The studies on nuclear resonant scattering by ⁴⁰K using synchrotron radiation are reviewed. Brilliant and high pure synchrotron radiation permitted us to observe the nuclear resonant forward scattering by ⁴⁰K in a powdered KCl sample, the excitation of which is impossible with ordinary radioactive sources. Furthermore, nuclear resonant inelastic scattering of synchrotron radiation by ⁴⁰K in the KCl sample at room temperature has been measured using a high-resolution monochromator. Adding to these, from the excitation experiments of ⁴⁰K, the energy and lifetime of the first excited state of ⁴⁰K were confirmed. These measurements clearly show that the studies on the electronic states through hyperfine interactions and the dynamical properties of potassium atoms, which are very important in material science and biology, are possible. It should be noted that ⁴⁰K is the natural isotope of potassium and weakly radioactive. Our observation of forward and inelastic scattering of the radioactive nuclide ⁴⁰K will lead to further studies on other radioactive nuclides the resonant forward and inelastic scattering of which are not observed to date.     

Solid Electrolytes Based on KAlO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>: The Crystalline Structure and Conduction

The structure of solid high-conductance potassium electrolytes K_{1 − x} Al_{1 − x} Ti_xO₂ (x = 0.1; 0.2) at 25 and 575°C is studied by a powder neutron diffraction analysis with the application of full-profile Rietveld analysis. Inserting titanium ions removes in potassium aluminate the phase transition at 540°C and the conductance anisotropy typical for its low-temperature form. Both structures are identical (fcc lattice, space group Fd3m). Experiment and calculation coincide best under the assumption that the potassium sublattice is disordered. The conductance increase upon inserting ions Ti⁴⁺ is due, apart from stabilization of the fcc structure, to formation of additional potassium vacancies and larger channels for the migration of potassium cations (ions Ti⁴⁺ are larger than ions Al³⁺).__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 878–883.Original Russian Text Copyright © 2005 by Burmakin, Voronin, Akhtyamova, Berger, Shekhtman.     

Radioargon production through the irradiation of calcium oxide

The production of radioargon through the irradiation of CaO was performed in an in-core facility within the The University of Texas at Austin MARK II TRIGA reactor. The major radioargon isotope produced was ³⁷Ar via the ⁴⁰Ca(n,α)³⁷Ar reaction pathway. The CaO powder was vacuumed sealed in a quartz ampoule. The sample was irradiated in a Cd-lined Al alloy canister for 2 h at 500 kW. After the irradiation, the sample was counted using an HPGe detector five times with increasing count times. ⁴¹Ar, ⁴²K, ⁴³K, and ⁴⁷Ca were detected in the spectra. The induced activities of ³⁷Ar, ³⁹Ar, ⁴¹Ar, ⁴²K, ⁴³K, and ⁴⁷Ca were calculated using a 63-group energy-dependent neutron flux determined utilizing a neutron energy flux profile calculated from a MCNPX model of the TRIGA reactor core. The production ratios generated from the model allowed for the estimation of induced ³⁷Ar and ³⁹Ar activities through the measured induced activities of ⁴¹Ar, ⁴²K, ⁴³K, and ⁴⁷Ca.     

On-stream nuclear activation of trace uranium and thorium using a 14 MeV neutron generator

A method for the continuous on-stream determination of trace concentrations of uranium and thorium in flowing streams is developed. The 14 MeV neutron generator was used for irradiation and the delayed neutron counting technique was employed in counting the induced neutron activity. The dependence of the minimum detectable concentration on the irradiation, decay and counting times, liquid flow-rate and the background was studied. At optimal conditions, uranium and thorium concentrations were determined down to 20 and 100 ppm, respectively. The interference of the neutron emitting nuclide^17m O was reduced to an insignificant level by optimizing the decay time.     

Neutron activation analysis for the determination of contaminants in food contact materials

A neutron activation method has been developed for the analysis of high density polyethylene, low density polyethylene, polypropylene, polyethylene terephthalate and polystyrene. Samples weighing 2–5 g were irradiated in a thermal neutron flux of 10¹⁶ neutrons m^–2 s^–1 and measured with gamma ray spectrometry for 64 elements. With the method developed here over 50 elements can be detected at concentrations below 1 mg/kg. Correction factors were applied for neutron flux variation and counting geometry.The method was validated using reference material citrus leaves (NIST) for Na, Mg, Al, K, Ca, Mn, Cu, Sr and I, and a suite of in house standards doped with Al, Cr, Co, Mg, Zn and Sb confirmed repeatability of the method. The method was used to measure inorganic contaminants in the raw polymers and retail samples of plastic packaging used in contact with food.