Determination of photopeak energy in instrumental neutron activation analysis

The precision and accuracy of the peak energy allocation in γ-ray spectrometry govern the subsequent computer processing of the data. By applying the main procedures for peak energy determination to a well-defined case, it is possible to define the minimal statistical uncertainties to be expected. The systematic bias of the energies obtained is caused mainly by changes in the total count rate. A correction can be applied based on the pulser peak. From the precision and the accuracy of the peak energy determination, the scanning width for automatic peak indexing follows.     

The precision and accuracy of iterative and non-iterative methods of photopeak integration in activation analysis,with particular reference to the analysis of multiplets

The relative precisions obtainable using two digital methods, and three iterative least squares fitting procedures of photopeak integration have been compared empirically using 12 replicate counts of a test sample with 14 photopeaks of varying intensity. The accuracy by which the various iterative fitting methods could analyse synthetic doublets has also been evaluated, and compared with a simple non-iterative approach.     

Gamma-ray photopeak interferences found in the instrumental neutron activation analysis of silicate rocks

Data are tabulated to identify all major and minor gamma-ray interferences which may effect the area determinations of analytical photopeaks for all principle isotopes (of half life greater than about one day) encountered during the routine instrumental neutron activation analysis of silicate rocks. These photopeaks cover the energy range 60–1700 keV and are based on data abstracted from ERDTMANN and SOYKA.⁸ Interferences are listed down to relative intensities of 0.001% and include principle sum peaks. Photopeaks which are considered to be most reliable for routine quantitative analysis are identified.     

A comparison of photopeak area computation methodologies

The accuracy and precision of photopeak area calculation methods has been studied by comparison of a digital method of computation with the fitting of a mathematical function to the data. In the present study, peak areas for 16 replicate photopeaks were computed both by the total peak area method any by the peak fitting method of program SAMPO. Both methods worked well with the fitting method showing somewhat smaller spread in the results.     

Evaluation of digital pulse processing-based gamma-ray spectroscopy under neutron activation analysis conditions

Digital signal processors are now available commercially for incorporation into high resolution gamma-ray spectroscopy systems. In this work, we have compared throughput, peak resolution and peak stability found in two Canberra 2060 Digital Spectrum Processors with a conventional analog processing setup in our laboratory. We have made the comparisons for five separate high purity germanium detectors which provide a range in detector size and construction. In addition, the range of input count rates chosen for study reflect those likely to be encountered in NAA. Our initial results indicate the performance to be detector specific and highly dependent on DSP setup parameters.     

A systems perspective to digital structures in molecular analysis

Within the last decade, the advance of miniaturization has opened the window to new systems that permit digital and molecular science to intersect, suggesting a new role for organic chemistry. Currently, fusion of molecules and electronic digits, as well as molecular-based digital structures, have expanded the conventional interpretation of the digit. This emergence has already generated new technological platforms with unique applications for molecular analysis and computation. We provide a brief overview of the conventional understanding of digital devices, examine the concept of molecular-based digits, and suggest new architectures by examining studies conducted on the compact discs. This analysis presents a perspective for the unique interaction of molecules and digits and the development of digital-based platforms for molecular analysis.     

A computer program for activation analysis

A computer program for calculating activation analysis results is described. The program comprises two gamma spectrum analysis programs, STOAV and SAMPO and one program for calculating elemental concentrations, KVANT. STOAV is based on a simple summation of channels and SAMPO is based on fitting of mathematical functions. The programs are tested by analyzing the IAEA G-1 test spectra. In the determination of peak location SAMPO is somewhat better than STOAV and in the determination of peak area SAMPO is more than twice as accurate as STOAV. On the other hand, SAMPO is three times as expensive to use with a Cyber 170 computer as STOAV.     

A gamma-spectrometry system for activation analysis

Based on a Preloaded Digital Filter operating on a 20% n-type HpGe detector with transistor reset preamplifier, and on a software implementation of a loss-free counting MCA, storing immediately into the multi-megabyte main memory of a low-cost 486-type PC, the new system enables the collection of up to 120 pairs of simultaneously recorded loss-corrected and non-corrected spectra of 16 k channels each, in a true sequence without time gaps in between, at a throughput rate of up to 140 kc/s. Intended for activation analysis of short-lived isomeric transitions, the system for the first time makes possible peak to background optimizations and even separations of lines with different half-lives without an a priori knowledge of sample composition by summing up appropriate numbers of spectra over appropriate intervals of time. The speed of this programmable system also made possible the direct comparison of two methods of real-time correction of counting loss, by simultaneous recording of LFC-corrected, ZDT^tm -corrected and non-corrected spectra together with their corresponding weighting factor distributions.     

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).     

A digital microfluidic method for dried blood spot analysis

Blood samples stored as dried blood spots (DBSs) are emerging as a useful sampling and storage vehicle for a wide range of applications. Unfortunately, the surging popularity of DBS samples has not yet been accompanied by an improvement in automated techniques for extraction and analysis. As a first step towards overcoming this challenge, we have developed a prototype microfluidic system for quantification of amino acids in dried blood spots, in which analytes are extracted, mixed with internal standards, derivatized, and reconstituted for analysis by (off-line and in-line) tandem mass spectrometry. The new method is fast, robust, precise, and most importantly, compatible with automation. We propose that the new method can potentially contribute to a new generation of analytical techniques for quantifying analytes in DBS samples for a wide range of applications.     

A technique for reducing interferences in epithermal neutron activation analysis

A new epithermal neutron activation technique is described. The technetium is based on the existence of non-overlapping resonance peaks in the neutron absorption cross-section spectra for the nuclides present in the sample to be analyzed. By this method it is possible to reduce some of the interfering activities with respect to the sought activity by using appropriàte filters. An experiment has been carried out to demonstrate the validity of the technique.     

A multi-element serum standard for neutron activation analysis

An annular ²²⁷AcBe isotopic neutron source, containing 6.6-Ci ²²⁷Ac, is described for application in fast and thermal neutron activation analysis, with high accuracy, for major constituents in ores, alloys and industrial concentrates. The characteristics of the neutron output and of the fast, epithermal and thermal flux and flux gradients is described in detail. The determination of manganese in pyrolusite ores and ferro-manganese is compared to results obtained previously with a cylindrical 1-Ci ²²⁶RaBe source. Two new sources of systematic errors have been discovered.     

A computer language for reducing activation analysis data

A program, written in FORTRAN, is described that defines a language for reducing activation analysis data. Communications are effected through commands, and these can be given in almost any order. Consistency checks are done and diagnostic messages are printed automatically to guard against the incorrect use of the commands. Default options on the commands allow instructions to be expressed concisely while providing a capability to specify details for the data reduction process. The program has been implemented on a UNIVAC 1108 computer.     

A digital microfluidic platform for primary cell culture and analysis

Digital microfluidics (DMF) is a technology that facilitates electrostatic manipulation of discrete nano- and micro-litre droplets across an array of electrodes, which provides the advantages of single sample addressability, automation, and parallelization. There has been considerable interest in recent years in using DMF for cell culture and analysis, but previous studies have used immortalized cell lines. We report here the first digital microfluidic method for primary cell culture and analysis. A new mode of "upside-down" cell culture was implemented by patterning the top plate of a device using a fluorocarbon liftoff technique. This method was useful for culturing three different primary cell types for up to one week, as well as implementing a fixation, permeabilization, and staining procedure for F-actin and nuclei. A multistep assay for monocyte adhesion to endothelial cells (ECs) was performed to evaluate functionality in DMF-cultured primary cells and to demonstrate co-culture using a DMF platform. Monocytes were observed to adhere in significantly greater numbers to ECs exposed to tumor necrosis factor (TNF)-α than those that were not, confirming that ECs cultured in this format maintain in vivo-like properties. The ability to manipulate, maintain, and assay primary cells demonstrates a useful application for DMF in studies involving precious samples of cells from small animals or human patients.     

A digital coding combination analysis for mutational genotyping using pyrosequencing

In the present study, we developed a novel digital coding combination analysis (DCCA) to analyze the gene mutation based on the sample combination principle. The principle is that any numerically named sample is divided into two groups, any two samples are not grouped in the same two groups, and any sample can be tested within the detection limit. Therefore, we proposed a specific combination that N samples were divided into M groups. Then N samples were analyzed, which could obtain the mutation results of M mixed groups. If only two groups showed positive (mutant type) signals, the same sample number from two positive signal groups would be the positive sample, and the remaining samples were negative (wild type). If three groups or more exhibited positive results, the same sample number from three positive signal groups would be the positive sample. If some samples remained uncertain, individual samples could be analyzed on a small scale. In the present study, we used the two genotypes of a mutation site (A5301G) to verify whether it was a useful and promising method. The results showed that we could quantitatively detect mutations and demonstrate 100% consistent results against a panel of defined mixtures with the detection limit using pyrosequencing. This method was suitable, sensitive, and reproducible for screening and analyzing low-frequency mutation samples, which could reduce reagent consumption and cost by approximately 70–80% compared with conventional clinical methods.     

Enhancement of digital gamma activation autoradiography capabilities by means of computer analysis of the time series images

It has been demonstrated that pixel-by pixel processing of series of autoradiography images for revealing the dynamics of decay of the induced radionuclides is an efficient approach for mapping of radionuclides in the sample in activation autoradiography. Concepts of virtual scanner and corresponding software for linearization of dependence of optical density on scanner response (luminosity) have been introduced. The concept provides unification of the subsequent processing of autoradiograms, irrespective of the method as to how the digital image has been obtained. Algorithms and the software for estimation of decay parameters of a radionuclide mixture for each pixel using a series of coaxially positioned images have been developed. The software is able generate a set of the derivative meta-images allowing a conclusion to be made about the presence of the inclusions in question. To increase the reliability of radionuclide mapping it is suggested to use analysis of distribution of half-life values estimated for pixels of image zone(s) pointed by a special mask.     

Substoichiometry in neutron activation analysis

A review is presented on the work done in development and applications of the substoichiometric techniques in neutron activation analysis.     

Derivative techniques in activation analysis

Derivative activation analysis is a technique in which the element or chemical entity to be determined is either replaced or complexed in a preirradiation chemical procedure with another element for which neutron activation analysis has an intrinsically higher sensitivity. Although the technique has many potential applications, the literature of the field is very limited. Examples of recent applications in our laboratory include: determination of P in natural waters, biological reference standards, brain tissue, rocks and coal; determination of Ni in a stony meteorite; determination of T1 in solutions; and speciation of oxygen (e.g., hydroxyl and carbonyl moieties) in coal via 14 MeV neutron activation.     

Primary standards in activation analysis

The availability of natural matrix reference materials evaluated for trace element content has resulted in their widespread use as standards (i.e., calibration materials; comparators) for instrumental neutron activation analysis (INAA). Due to the uncertainties associated with their certified values, the limited number available, and the relative matrix independence of INAA, these reference materials are more properly utilized as quality assessment materials, after calibration of the INAA analytical system with true primary standards. Terminology is defined, the use of matrix reference materials to evaluate the analytical system is discussed, techniques for the accurate preparation of primary standards for trace element analyses are reviewed, and necessary precautions in the accurate comparison of samples to standards are presented.     

Nuclear interferences in activation analysis

Calculations of some first- and second-order interferences at various values of the cadmium ratio (R) have been performed for cases important in activation analysis. A sharp nonlinear dependence of second-order reaction yields on low R values has been shown. Calculated yields for some reactions have been studied experimentally.