Compton suppression neutron activation analysis: Past,present and future

Conclusions In this work a review of the development of compton suppression is presented. It was shown that the application of Compton-suppression counting in instrumental NAA reduces the detection limits and improves the accuracy for a list of elements by substantial reduction of the background of the -spectroscopy. Results for certified reference materials obtained through the use of Compton suppression are normally more accurate and in agreement with the published values. Compton suppression is particularly helpful for low level concentrations in environmental samples to those elements which exhibit severe special interferences in the normal NAA counting. A list of the elements with isotopes having single or close to single -ray decay schemes and which could benefit from Compton-suppression counting is presented. Also, evaluation is made regarding the reliability of Compton suppression with increase in the overall dead-time of the counting. It was concluded that this method does not provide accurate quantification of the isotopes when the overall dead-time exceeds the 10% range. Investigation of the natural background was performed with Compton suppression for the purpose of neutron activation analysis application. The method presented proves to broaden the application of NAA and helps in its competition for simplicity, accuracy and reliability with the modern methods of elemental analysis. Future application of coincidence spectrometry in activation analysis should include better enclosing of the primary detector, utiliza5tion of x-ray and well type detectors, -, -, and -- coincidence techniques.     

Die zerstörungsfreie Bestimmung der Seltenen Erdelemente nach der Neutronenaktivierung

The technique of INAA for the determination of the rare earth elements with respect to prospecting and production testing of polishing powders on the basis of rare earth element oxides as well as quality testing of ultragrade rare earth compounds is discussed.In order to count -radiation of the radioactive nuclei a Ge-Li-detector as well as a planar Ge-Li-detector have been used. The latter enables the evaluation of the low energetic side of the -spectrum without complicated corrections due to -line interferences. Therefore an efficient working procedure with respect to the determination of the distribution pattern of the rare earth elements is possible.A simple correction program however is necessary with respect to the use of the planar detector type, allowing for effects of self-absorption geometry of the sample as well as distance sample-detector. This program is also given in the paper.

     

Determination of Al,Ca, V and Mn by INAA: Application to the Reference Material IAEA-395 “Urban Dust”

Instrumental NAA based on short-lived radionuclides implies high initial total count rates which change appreciably over the counting period. This in turn necessitates corrections for three negative biases: losses due to differences in counting time between samples and standards; pile-up losses, and (residual) influence of dead-time. The procedure is demonstrated for the determination of Al, Ca, V and Mn in the IAEA Reference Material 395 Urban Dust. The obtained data are in good agreement with the reference values for this material. By limiting the total relative dead-time to 25%, statistical uncertainties are below 5%.     

The advantage of anti-Compton counting in the measurement of low-level radioactivity by gamma-ray spectrometry

The inherent advantage of anti-Compton counting of low-level radioactivity is defined in terms of changes in the limits of decision, detection and determination. It appears that the advantage factor can be expressed in the experimentally observed reductions of peak area, compton continuum and natural background. For an array equipped with a sample changer, the advantage factor for interference by the compton continuum is 4, while that for interference by the natural background amounts to 3. By sacrificing the sample changer and closing its gap with NaI-plug, additional factors of 1.5 and 2 can be obtained for compton and natural background, respectively.     

Radon measurement by coincidence gamma-ray spectrometry

A method of radon measurement by a multidetector -ray spectrometer,based on coincidence counting of 609 keV photons from two-step cascade transitionsthat follow â – decay of 214 Bi, is proposed. Besides a good accuracy,the method has better sensitivity than some standard methods of radon measurementcurrently in use. Applying this method to the PRIPJAT-2M spectrometer with6 NaI(Tl) detectors, and counting a 1 l sample of well water for 30 minutes,a minimum detectable radon activity of 0.25 Bq/l is experimentally determined.     

Determination of the reactive surface area of silica

Summary The surface area available for reaction in silylation reactions has been determined by reaction of the silica with a radioactively labelled alkyldimethylchlorosilane followed by liquid scintillation counting of either a solid or a dissolved silica sample. The results are compared with values obtained by nitrogen adsorption and the pore size distributions of the products before and after reaction.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Recent progress and application of low level liquid scintillation counting

The use of an ultra low level liquid scintillation counter with extremely low background, MCA technique, storage and software evaluation of pulse height spectra has given very low LLD's, the possibility of - and -spectrometry to some extent and time saving optimization of counting conditions. Quick and very simple but yet accurate analytical methods could be worked out worked out for environmental measurements: Environmental levels of tritium,¹⁴C in several assimilation products,²²²Rn and²²⁶Ra in water without any sample pretreatment. Suggestions for possible further applications in environmenial monitoring and low level counting are given.     

Rapid and simultaneous determination of U,F, Al,Ca and V in phosphate rocks by a combination of delayed neutron and γ-ray spectrometry techniques

Delayed neutron counting for uranium assay was coupled with -ray spectrometry in order to measure radionuclides of F, Al, Ca and V produced by neutron activation. For this measurement, the delay time required for U determination was exploited. Calibration of the method was provided by standards based on a CaCO₃ matrix and validity of results was verified against other analytical methods. A single sample can be analyzed for the five elements in 3 min with a precision of ±10%. The method developed was applied in the exploration of phosphate ores. The measured total concentrations permitted the disclosure of correlations between various elements and constituents in the samples. Chemical and mineralogical properties were obtained as well.     

Methods for preparing comparative standards and field samples for neutron activation analysis of soil

One of the more difficult problems associated with comparative neutron activation analysis (CNAA) is the preparation of standards which are tailor-made to the desired irradiation and counting conditions. Frequently, there simply is not a suitable standard available commercially, or the resulting gamma spectrum is convoluted with interferences. In a recent soil analysis project, the need arose for standards which contained about 35 elements. In response, a computer spreadsheet was developed to calculate the appropriate amount of each element so that the resulting gamma spectrum is relatively free of interferences. Incorporated in the program are options for calculating all of the irradiation and counting parameters including activity produced, necessary flux/bombardment time, counting time, and appropriate source-to-detector distance. The result is multi-element standards for CNAA which have optimal concentrations. The program retains ease of use without sacrificing capability. In addition to optimized standard production, a novel soil homogenization technique was developed which is a low cost, highly efficient alternative to commercially available homogenization systems. Comparative neutron activation analysis for large scale projects has been made easier through these advancements. This paper contains details of the design and function of the NAA spreadsheet and innovative sample handling techniques.     

VIZR—an automated chemometric technique for metabolic profiling

A chemometric technique, visual interpretation of z-score ratios (VIZR), written in the open source code R, has been developed to identify metabolic differences between individual biosamples and a control group. To demonstrate the capabilities of VIZR, 49 urine samples were collected from healthy volunteers: 41 samples were collected randomly following a normal dietary routine and 7 test samples were collected after dietary supplementation with either ibuprofen or alcoholic beverages. An eighth test sample was prepared by 50 % dilution of a control sample. Sample analysis was conducted by ¹H nuclear magnetic resonance (NMR) spectroscopy and the collected data were subjected to VIZR analysis, which successfully discriminated each of the 8 test samples from the 41 control samples. In addition, VIZR analysis revealed the NMR spectral regions responsible for the disparity between the individual test samples and the control group. The self-normalizing nature of the VIZR calculation provides a robust analysis independent of dilution effects, which is especially important in urine analyses. Potential applications of VIZR include high-throughput data analysis for toxicological profiling, disease diagnosis, and biomarker identification in any type of biosample for which a control dataset can be established. Although demonstrated herein for the statistical analysis of ¹H NMR data, the VIZR program is platform independent and could be applied to digitized metabolic datasets acquired using other techniques including hyphenated mass spectrometry measurements.

Correction factors required for quantitative large volume INAA

Extension of current INAA practice to accommodate large volume samples, of the order of 0.1 to 1 m³, requires consideration of the need for correction factors that are usually negligible for most small sample analyses. Direct INAA of large samples can be advantageous for materials that are not homogeneous such as contaminated soil, industrial raw materials or solid wastes. Large sample INAA can be adapted for the screening of such materials in situations when representative small samples would be difficult or tedious to obtain and analyze. However, appropriatecorrections are required to take into account neutron flux attenuation and gradients within large samples as well as absorption losses of emerging -rays and extended counting geometry. In this work, thermal neutron flux attenuation over several cm within a SLOWPOKE reflector site was measured, using monitors, to amount to 0.84 of incident flux and the quantitative sample self-shielding factors for cylindrical C₁₂H₂₂O₁₁ samples, were modeled within ±3% through adaptation of published values. Gamma-ray attenuation and variation in counting geometry over sample dimensions were experimentally determined and compared to calculated correction factors. Their computation was based on sample-detector geometry and utilized linear -attenuation coefficients of sample matrix and air. Similarly, agreement of large sample SRM's measured concentrations with certified values was within <5%, thus validating the use of these methods and their future extension to large volume sample INAA.     

Accuracy and applicability of the k0-standardization method

The present paper deals with the accuracy and applicability of the k₀-standardization technique in NAA. Topics included are: user-oriented outline of the method, relevant nuclear data (k₀, Q₀, tc.), the non-1/E epithermal flux distribution, small detector separations and/or extended source geometries, (n, ) reactions with a Westcott-g1, primary interferences, subsequent (interrupted) irradiations, the non-constancy of the neutron flux during irradiation, and a final account of the accuracy. Although the paper is written in terms of the k₀-methodology, a good deal of the considerations can be transferred to most types of single-comparator standardization.     

Spectral and non-spectral interferences in inductively coupled plasma mass-spectrometry

Inductively coupled plasma mass spectrometry of environmental and biological samples is often hampered by spectral and non-spectral interferences. Spectral interferences, caused by the limited resolution of the quadrupole mass spectrometer, can be eliminated in a variety of ways. For their identification inspection of a signal versus carrier gas flowrate is useful. Anion exchange allows the removal of most S and Cl containing compounds, which are at the origin of the majority of spectral interferences. Matrix modification, for example the addition of ethanol and subsequent optimization of the gas flow rates in a number of cases enables the reduction of the interferences to insignificant values. Often a mathematical correction based on isotopic signal ratios can be applied. Non-spectral interferences can be divided in reversible, that is occurring while the sample is being measured, and irreversible matrix effects, that is clogging of the nebulizer and sampling orifices or deposition on the torch or in the ion lens stack. The errors associated with non-spectral interferences can be eliminated by appropriate calibration procedures, adapted sample preparation or limitation of the amount of sample delivered to nebulizer, plasma and sampling devices, for example by the application of flow injection. Applications of all the elimination procedures are described for the analysis of sea-water, estuarine water, soil and sewage extracts, percolate water, urine, serum and wine.     

Complexometric determination of cadmium using 2-Mercaptoethanol as masking reagent

A complexometric method for the determination of cadmium(II) in presence of other metal ions is described based on the selective masking ability of 2-mercaptoethanol towards cadmium(II). Cadmium and other ions in a given sample solution are initially complexed with excess of EDTA and the surplus EDTA is titrated with lead nitrate solution at pH 5.0–6.0 (hexamethylentetramine), using xylenol orange as indicator. A known excess of 2-mercaptoethanol solution (10% alcoholic) is then added, the mixture is shaken well and the released EDTA from the Cd-EDTA complex is titrated against standard lead nitrate solution. The interferences of various ions are studied and the method is applied to the determination of cadmium in its complexes. Reproducible and accurate results are obtained for 3.5–25mg of Cd with relative errors 0.65% and standard deviations 0.06 mg.     

MS Interview: An elemental mass spectrometry spectral interference data base

A graphically-oriented data base of spectral interferences dut occur in inductively coupled plasma-mais spectrometry and glow discharge-mass spectrometry has been developed. The program is called “MS Interview” and runs on a Macintosh computer. The program allows one to specify which technique (ICP or GD) the various interferences will be presented for, and for the case of the ICP, the acid matrix background. Bated on these parameters the program provides a listing of interferences broken down into the following categories: Isobarics, Oxides, Doubly Charged Species, Background Dependent, and Matrix Dependent. For the glow discharge case there are two additional categories: Argides and Dimers. Interference information is provided for all masses of all elements and is easily accessed via mouse operations from a periodic table window and element mass spectral windows. The program is expandable to include other ion sources and interferences can be added or deleted as required by the user. Finally, the program also includes a small library of typical background spectra that can be displayed and manipulated. This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta B (SAB). The hardcopy text is accompanied by a disk containing the program MS Interview, a manual, a reference list, and a bar graph format mass spectral library of the elements.     

A multi-detector integrated automation system of routine INAA

An integrated automation system of routine instrumental neutron activation analysis (INAA) with three HPGe detectors has been built at China Institute of Atomic Energy. This system is mainly composed of sample counting system, pneumatic transfer system, software control and analysis systems, etc. The characteristics include more than 200 samples can be controlled for a batch of INAA with three detectors simultaneously, sample counting position can be optimized automatically according to the counting dead time, the real-time tracking and the high consistency between the spectrum and counting sample are possible to be realized through radio frequency identification tag.

     

Development of a computer-based system for fast neutron cyclic activation analysis

We have developed a computer-controlled system for carrying out cyclic neutron activation analysis using fast neutrons. The system is basically a mechanical, pneumatic transfer system in which the sample is cycled between an irradiation position and a Ge detector. The sequence of movements between these two position is under computer control as is the timing of the various parts of the cycle. In addition, flux monitoring and correction are carried out using a computer-controlled scaler and the -ray counting is similarly controlled. The key to this control is the use of an interface containing a DCP BUS which receives signals from various valves for control of sample movement or to the scaler or ADC to initiate counting storage or calculations of the data. Finally, some preliminary data obtained with this technique are presented for the inelastic scattering reactions on barium.     

Measurement of strontium-90 by the Cerenkov counting technique

Our laboratory is responsible for monitoring natural and artificial radioactivity in components of human food chains in French Polynesia. One of the artificial radioisotopes of particular interest is strontium-90, which comes from worldwide fallout. This nuclide is a high yield fission product (5%) with a long half-lie (28 y). Strontium-90 is also a pure -emitter and, consequently, requires good chemical separation prior to counting. LESE is required to analyze about 1000 samples per year and therefore does not perform yttrium-90 separation on each sample. Our analytical procedure thus gives an equivalent strontium-90 value. Until 1990, results given to the UNSCEAR were slightly above the true strontium value due to radium decay product interferences. To reduce these interferences, LESE now uses the Cerenkov technique which permits the elimination of low-energy -emissions. The final results are still expressed as equivalent strontium-90, but they are closer to the true value.     

A new microcomputer program for processing data in neutron activation analysis

A new utility program for processing data in neutron activation analysis (NAA) has been developed for use on MS-DOS microcomputers. Peak areas are read from ASCII data files of gamma-ray spectra which have been processed by a Gaussian peak fitting program, GAMANAL-PC. Elemental concentrations are then calculated by this new program, QUACANAL, via a semi-absolute algorithm that uses pre-determined activation constants. User-defined ASCII library files are employed to specify the elements of interest required for analysis, and (n, p) and (n, ) interferences are taken into account. The program has been written in turbo PASCAL, is menu driven and contains options for processing data from cyclic NAA. An interactive philosophy has been used in designing the program.Sabbatical address for 1991/1992.     

The determination of241Pu by liquid scintillation spectrometry using the Packard 2250CA

The results of this study indicate that in terms of efficiency, the Packard 2250Ca liquid scintillation spectrometer is sensitive to the scintillation cocktail employed for²⁴¹Pu analysis, particularly when the burst counting circuit is enabled. Cocktails exhibiting low t-SIE values should be avoided since quenching has a critical influence on such a low energy ^– emitter. This effect would be independent of burst circuitry use. Cocktails which include naphthalene type derivatives such as the alkylnaphthalene solvent employed in Optiphase HiSafe 3 and Ultima Gold should be avoided since the broad pulse shapes produced are incompatible with the burst counting circuit which distinguishes background events from true ^– events by means of pulse shape/duration analysis. Efficiency is also sensitive to the concentration of bis-MSB employed in conjunction with the primary fluor. Enhancements in efficiency are observed with appropriate concentrations. These results are in line with previous work with¹⁴C and are postulated as being a consequence of sharpening prompt pulse widths or suppression of afterpulsing. It is recommended that Instafluor should be used to maximize response, or a cocktail such as butyl-PBD/bis-MSB in pseudocumene at rates of 6 and 1.5 mg ml^–1, respectively, where a lower vapor pressure solvent is particularly required.