Development of irradiation conditions for neutron activation analysis of inorganic trace impurities in plastics for microelectronic applications

The difficulties of analyzing plastics of high purity by chemical analysis methods have led to the application of neutron activation analysis. Because literature quotes pressure build-up in the irradiation containers as the reason for limited activation intensity the behavior of the six plastics PVI, PMMA, PVDF, PE, FEP and Silicone had to be investigated. The investigations showed, that pressure build-up was not the limiting factor. Furthermore hydrogen generation under irradiation seems to be the reason for explosions of ampoules by an oxyhydrogen reaction. The question of the ignition source could not be answered yet. To prevent oxyhydrogen reaction, the ampoules have to be filled with nitrogen. The experiments have shown, that if suitable sample masses and ampoule volumes are selected, even high neutron fluences can be applicated. After determining the permissible irradiation conditions, the impurity content of 30 elements in the six plastics were determined using destructive and nondestructive NAA.     

High-Flux Irradiation of Open Samples

The irradiation of large samples of biological material in a high neutron flux enables the extention of trace element analysis into the ng to pg range, but raises several problems as gamma heating and radiolysis degrade the samples. Gamma heating increases the pressure to a point where either a very large irradiation container is necessary or a container which can endure the high pressure. Several methods to overcome these problems have been published. The irradiation of open samples was performed as an alternative to these methods. Temperature effects on biological material during irradiation in a high and in a low neutron flux were compared. As an example, wheat was irradiated in open containers allowing simultaneous temperature measurement in the sample during irradiation.     

Evaluation of high purity graphite sample containers for use with rapid instrumental epithermal neutron activation analysis

The suitability of graphite of spectral quality as a sample container in short irradiations for neutron activation analysis has been investigated. The material is found to be a viable alternative to polyethylene containers especially in high flux irradiation positions where the properties of the latter deteriorate as a result of high neutron and gamma dose rates. Examples of application are demonstrated in epithermal neutron irradiations of biological materials and the accuracy and precision of the determinations were assessed.     

An accurate and sensitive analysis of trace and ultratrace metallic impurities in plastics by NAA

Neutron activation analysis (NAA) has been studied to improve the accuracy and sensitivity of the analysis of trace and ultratrace metallic impurities in plastic materials. There are two main problems in the analysis of plastics by NAA. First the contamination during sample preparation, especially sample crushing procedure is very serious for ultratrace analysis. Another problem is the destruction of the sample capsule due to the pressure build-up by the gases formed during neutron irradiation. A simple preparation technique of the sample crushing method using liquid nitrogen and reducing the capsule pressure by a pin hole was developed to solve the above problems. Two different irradiation and seven cooling conditions were also investigated to optimize the experimental conditions. A SRM from NIST (1632b coal) has been used to investigate the accuracy of the analysis. More than thirty elements could be analyzed in the range of sub-ppb to percent. Samples analyzed in this work were polyethylene and polypropylene which were made by different manufacturing procedure, and pigments. Two kinds of plastic products used for food and drug containers were also analyzed. It was found that NAA could be a powerful technique for the analysis of metallic impurities in plastics even though their concentrations were at ultratrace levels.     

Determination of leachable arsenic from glass ampoules

Appreciable amounts of different arsenic compounds are used in the manufacture of glass and glass ampoules (injection vials and bottles) used to store drugs. Exposure/intake of arsenic to human beings may result in skin ulceration, injury to mucous membranes, perforation of nasal septum, skin cancer and keratoses, especially of the palms and soles and may cause detrimental effects. Considering the toxicity of arsenic, even if traces of arsenic from such glass containers/ampoules are leached out, it can impart damage to human beings. To check the possibility of leaching of arsenic from glass ampoules, a simple methodology has been developed. Different makes and varieties of glass ampoules filled with de-ionized water were subjected to high pressure and temperature leaching for varying amount of time using autoclave to create extreme conditions for the maximum leaching out of the analyte. Subsequently, the determination of the arsenic contents in leached water using neutron activation analysis is reported in this paper in detail with observations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Minimization of the blank values in the neutron activation analysis of biological samples considering the whole procedure

In our determination of trace element contents of animal tissue by neutron activation analysis in the course of structure-activity relationship studies on platinum containing cancer drugs and wound healing we have tried to minimize the blank values that are caused by different sources of contarnination during surgery, sampling and the activation analysis procedure. The following topics have been investigated: the abrasions from scalpels made of stainless steel, titanium or quartz; the type of surgery; the homogenisation of the samples before irradiation by use of a ball mill; the surface contaminations of the quartz ampoules that pass into the digestion solution of the irradiated samples. The appropriate measures to be taken in order to reduce the blank values are described. The results of analyses performed under these conditions indicate the effectiveness of the given measures, especially shown by the low values obtained for the chromium contents of the analysed muscle samples.     

Radiological risks from irradiation of cargo contents with EURITRACK neutron inspection systems

The radiological risk for the population related to the neutron irradiation of cargo containers with a tagged neutron inspection system has been studied. Two possible effects on the public health have been assessed: the modification of the nutritional and organoleptic properties of the irradiated materials, in particular foodstuff, and the neutron activation of consumer products (i.e. food and pharmaceuticals). The result of this study is that irradiation of food and foodstuff, pharmaceutical and medical devices in container cargoes would neither modify the properties of the irradiated material nor produce effective doses of concern for public health. Furthermore, the dose received by possible stowaways present inside the container during the inspection is less than the annual effective dose limit defined by European Legislation for the public.     

Reduction of beta-interference in gamma-spectrometric measurements of neutron-irradiated geological material

The analytical technique for instrumental neutron activation analysis, when applied to geological materials, is improved by introducing an lectromagnetic field between sample and detector. This field lowers the bremsstrahlung background intensity in the gamma-spectrum, by reducing the number of beta-particles reaching the detector. Thus, precision, accuracy and lower detection limit are improved. In this work the technique has been used on an alkalisyenite and on meteoritic material, rocks containing high quantities of sodium and iron, respectively. After neutron irradiation, the induced nuclides²⁴Na and⁵⁹Fe are responsible for high bremsstrahlung interference, which under normal analytical conditions would mask any X-ray or gamma-ray peaks of interest. The technique is easily applied to multielement analysis of geological and biological material (although the latter is not treated in this paper). It can be combined with sophisticated spectrum-treating techniques such as spectrum stripping and spectrum smoothing, or coincidence-anticoincidence circuits.     

Neutron activation analysis of Th via233Pa

A method is described for the analysis of thorium by neutron activation. The sample is brought into solution and quantitative extraction of²³³Pa is carried out in 1M HNO₃ using 0.5M HTTA in benzene. Extraction mechanisms are discussed. The use of a low-power reactor (100 kW_th) enables determination of thorium at a lower concentration limit of 50 ng for periods of irradiation, cooling and measurement of 3 hours, 24 hours and 300 seconds, respectively.     

The NAA system at the reactor BER II clinical analysis of fluorine,calcium, phosphorus and aluminium in bone biopsies,comparison with photon activation analysis and ion sensitive electrode

Over the past few years an irradiation and measuring system has been developed for the reactor BER II at the Hahn-Meitner-Institut. It was to be suited in particular to the neutron activation analysis of biological material via short lived radionuclides. The general characteristics of this equipment and some experimental details as the recycling facility and the device used for measuring the irradiation time, the waiting time and the neutron fluence are described. This equipment was used to determine physiological concentrations of the elements sodium, chlorine, aluminium, phosphorus, fluorine, calcium, copper and selenium in biological material. The results have been compared with those obtained by photon activation analysis or ion sensitive electrode. We report on the clinical analysis of Ca, F, P and Al in the control of the treatment of osteoporosis patients and of patients undergoing haemodialysis over long periods as an example of the application of the apparatus. Arbeitsgruppe Spurenelemente in der Biomedizin     

Gamma ray spectra and sensitivities for 14 MeV neutron activation analysis

The purpose of this study was to define experimentally the sensitivity of determination for 63 different elements by 14 MeV neutron activation, with a 150 kV Cockroft-Walton accelerator at a neutron flux of 2·10⁸ n·cm⁻²·sec⁻¹ on the sample. The obtained gamma ray spectra are given, and the origin of the photopeaks observed are explained. A maximum irradiation time of five minutes was used as a convenient experimental limit to obtain the maximum sensitivity, considering, however, that the tritium target life is limited, and that the time to perform an analysis has to be reasonable. The practical use of 14 MeV neutron activation analysis is demonstrated by the detection limits obtained.     

Instrumental neutron activation analysis of samples with volumes from 2 to 350 ml

Usually neutron activation analyses are performed in point-source geometry. However, specially designed irradiation positions and carefully planned measuring conditions enabled the activation and analysis of samples with weights up to several tens of kilograms. A dedicated character of irradiation and of measuring conditions was the main reason for a very limited application of such activation analysis. The use of routine irradiation facilities and standard conditions for analytical gamma-spectrometric measurements is described. Starting with samples of some hundred milligrams usually used in activation, through multi-gram samples to several hundred gram samples, irradiation and measuring conditions were studied and tested for development of the method. This work began in 1991 in Denmark, using the Danish DR-3 reactor. Since then different aspects of the method have been investigated on 6 reactors; in Denmark on DR-3, in Austria on Triga-MkII (in Vienna), and Astra (in Seibersdorf), in the German Federal Republic on FRG-1 in Geesthacht, in Norway on Jeep II (in Kjeller), and in Kazakhstan on VVR-K (in Alatau). Altogether more than 1000 samples have been irradiated and measured. In total, the roughly 30 kg of irradiated materials included almost 300 large samples of more than 30 gram weight. The following theoretical and practical aspects were investigated during the work: theoretical problems concerning neutron self-absorption in common organic and inorganic materials, as well as gamma-attenuation during the measurement. From a more practical point of view: health physics and radiation hazards during irradiation, measurement, transportation and storage of samples with several hundred grams weight. Special requirements to irradiation containers were formulated and various containers were tested. Main advantages and drawbacks of the method are discussed.     

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.     

Determination of total mercury in environmental and biological samples using k0-INAA, RNAA and CVAAS/AFS techniques: Advantages and disadvantages

The accuracy and precision of the results obtained for total mercury in various environmental and biological samples and certified reference materials (CRMs) by various analytical methods, including k ₀-instrumental neutron activation analysis (k ₀-INAA), radiochemical neutron activation analysis (RNAA) and cold vapour atomic absorption (and atomic fluorescence) spectrometry (CVAAS/AFS) used in routine analysis in our laboratory, were investigated. Three natural matrix reference materials (RMs) from the International Atomic Energy Agency (IAEA), five CRMs from the Institute for Reference Materials and Measurements (IRMM), six CRMs from the National Institute of Standards and Technology (NIST) and one from the Jožef Stefan Institute (IJS) were analyzed. The results obtained show good agreement between certified or assigned values, and between the methods used, except for some data obtained by k ₀-INAA in biological samples. This can be explained by losses during irradiation in semi-open systems (irradiation in plastic ampoules) and/or spectral interferences. This revised version was published online in August 2006 with corrections to the Cover Date.     

Non-destructive determination of zinc in biological certified reference materials

Non-destructive neutron activation analysis was employed to determine zinc in ten biological standard reference materials from the National Bureau of Standards and the National Research Council of Canada. The use of a 4 h. irradiation at a medium neutron flux allows excellent accuracies, precision and sensitivities to be attained for all the samples analyzed. It is suggested that neutron activation analysis be one of the benchmark methods for the determination of zinc in biological reference materials for concentrations as low as the one part per million level.     

Determination of trace elements in water by non-destructive neutron activation

A systematic study was undertaken in order to find out which of the most relevant elements can be determined in water under normal conditions by non-destructive neutron activation simultaneously using a suitable monostandard method. Standardized water samples as well as natural water of different kind were used, brought to dryness by freeze-drying and irradiated in quartz at a neutron flux of 10¹⁴ cm⁻² s⁻¹ for 1 day. The trace element content in quartz ampoules of different origin was determined separately. The following elements are discussed in detail including possible interferences: As, Au, Br, Ca, Cd, Co, Cr, Cu, Eu, Fe, Hg, K, La, Mo, Na, Ni, Sb, Sc, Se, U, Zn. Presented at the Euroanalysis II Conference, Budapest, 25–30. Aug. 1975.     

NAAPRO: A code for predicting results and performance of neutron activation analysis

Summary A code is described for predicting the results and main characteristics of neutron activation analysis (NAA) on the basis of a simulated gamma-ray spectrum of activation products, calculated for the specified analysis conditions. These are analysis time mode, analyzed sample mass and elemental composition, characteristics of the irradiating neutron flux and irradiation conditions, gamma-spectrometry measurement geometry and background conditions, as well as detector and spectrometry system parameters. Gamma-ray dose rates for different points of time after sample irradiation and input count rate of the spectrometry system are also predicted.     

Automatic microanalyzers: I. Automatic introduction device

An automatic introduction device AID which can be used to introduce automatically a sample container made of quartz, silver, aluminum or other material into a pyrolysis or combustion tube is described.This system which consists of two parts, the sample inlet device, made of Pyrex glass, and the collecting tube, made of quartz, is very simple and cheap.Gravity feed is used to introduce the sample containers into the AID; the used containers heap up on the bottom of the collecting tube which has to be changed only when it is full so that it is no longer necessary to withdraw each used container after every single determination.The change of the collecting tube which lasts about 0.25 leaves the microanalyzer in working condition.The AID enabled us to develop several apparatus such as oxygen, carbon-hydrogen and nitrogen microanalyzers with a complete automatic control; they will be described in other papers.     

Loss of elements in the oxygen flask decomposition of biological materials: A study by neutron activation analysis

Partial loss of elements in the oxygen flask method for the decomposition of biological materials is described. The irradiated sample is placed in a platinum wire gauze or quartz cup and burnt in an oxygen atmosphere in the presence of carrier solutions. The results obtained by radiochemical neutron activation analysis for the elements like Mn, As, Cu, Sb and Zn in different standard reference materials are presented with a discussion of the possible causes for the lower values.     

Cyclic activation analysis—A review

The setting of cyclic activation and its development in a historical context is attempted and a case is made for the usefulness of the method in the analysis of materials via short-lived isotopes. The theory of cyclic activation analysis is presented and the resulting detection limits shown to be superior to the conventional one-shot irradiation-counting sequence. The possibility of determining the half-life of an isotope from the data accumulated in the same experiment is also highlighted. Problems and applications are illustrated by experimental results obtained from a variety of sample matrices, mainly biological and environmental, with the use of a reactor irradiation facility, since the use of both isotopic neutron sources and neutron generators are discussed elsewhere. It should therefore be viewed as a personal and selective review of the field. Epithermal cyclic neutron activation analysis is suggested as an area demanding consideration and a new cyclic activation system is introduced. Dedicated to the memory of Dr. BASILEIOS GEORGOUDIS, surgeon and gynaecologist (d 2nd January 1980).