Formulas for the precision and accuracy of137Cs measurements and of the consumer's and producer's risks in routine control are given. The limit of determination is determined by the combination of natural background, compton continuum of the sample aliquot, counting efficiency and the residual uncertainty in positioning.
Authors:G. Ónodi, Gy. Kröel-Dulay, E. Kovács-Láng, P. Ódor, Z. Botta-Dukat, B. Lhotsky, S. Barabás, J. Garadnai, and M. Kertész
Aboveground plant biomass is one of the most important features of ecosystems, and it is widely used in ecosystem research. Non-destructive biomass estimation methods provide an important toolkit, because the destructive harvesting method is in many cases not feasible. However, only few studies have compared the accuracy of these methods in grassland communities to date. We studied the accuracy of three widely used methods for estimation of aboveground biomass: the visual cover estimation method, the point intercept method, and field spectroscopy. We applied them in three independent series of field samplings in semi-arid sand grasslands in Central Hungary. For each sampling method, we applied linear regression to assess the strength of the relationship between biomass proxies and actual aboveground biomass, and used coefficient of determination to evaluate accuracy. We found no evidence that the visual cover estimation, which is generally considered as a subjective method, was less accurate than point intercept method or field spectroscopy in estimating biomass. Based on our three datasets, we found that accuracy was lower for the point intercept method compared to the other two methods, while field spectroscopy and visual cover estimation were similar to each other in the semi-arid sand grassland community. We conclude that visual cover estimation can be as accurate for estimating aboveground biomass as other approaches, thus the choice amongst the methods should be based on additional pros and cons associated with each of the method and related to the specific research objective.
Authors:R. Zeisler, R. Demiralp, and M. Makarewicz
A source of error in the gamma-spectrometric registration of the analytical signal in neutron activation analysis is its dependency on the overall count rate. Losses in the accuracy of quantitation occur due to hardware and software. This paper presents examples for solutions to these problems and demonstrates that accurate NAA can be accomplished under high-rate counting conditions with commercially available technology.
A mixture of233Pa,140La,82Br,64Cu.72Ga,60Co, and24Na of known disintegration rates was counted on a NaI(Tl) and a large Ge(Li) detector. Both systems detected233Pa when present at 0.2%, and accurate results were observed for233Pa,140La, and60Co when present at greater than 0.5% of the total disintegration rate. The accuracy of the results from either system was
not significantly different since the mean ratio of the observed to true results was 0.99±0.05 and 1.06±0.06, respectively.
However, equal sensitivity and accuracy were achieved only when the counting interval for the germanium system was 1000 min,
or 60 to 600 times that for sodium iodide.
The k1-method for standardization in INAA specifically tackles the problem of the interpretation of gamma-ray spectra as obtained with highly efficient detectors, as opposed to the k0-method. In this paper, results obtained from three NIST reference materials, measured after neutron activation with a gold-lined well-type detector, are presented. It is concluded that the accuracy of the method is better than 1%.
A greater understanding of the inaccuracies involved inin vivo measurements of liver and kidney cadmium by neutron activation was necessary. Studies were therefore carried out, using phantoms, into the effect onin vivo measurement accuracy of organ depth and organ mass. In addition an independentin vitro technique was developed, and used to analyse autopsy samples from three people previously measuredin vivo, thus making direct comparisons possible. No evidence of bias in thein vivo results was found, but the need to correct for organ mass and depth was highlighted. Current measurement procedures result in residual uncertainties of ±25%.
Neutron activation analysis is one of many analytical techniques used at the National Institute of Standards and Technology (NIST) for the certification of NIST Standard Reference Materials (SRMs). NAA competes favorably with all other techniques because of it's unique capabilities for high accuracy even at very low concentrations for many elements. In this paper, instrumental and radiochemical NAA results are described for 25 elements in two new NIST SRMs, SRM 1515 (Apple Leaves) and SRM 1547 (Peach Leaves), and are compared to the certified values for 19 elements in these two new botanical reference materials.
Authors:Nouruddin W. Ali, Eglal A. Abdelaleem, Ibrahim A. Naguib, and Fatma F. Abdallah
A validated, sensitive, and highly selective stability-indicating high-performance thin-layer chromatographic (HPTLC) method has been adopted for the quantitative determination of pyridostigmine bromide in the presence of its alkaline-induced degradation product and in pharmaceutical formulations. 3-hydroxy-N-methyl pyridinium bromide (3-OH NMP) is the metabolite, impurity, and alkaline-induced degradation product of pyridostigmine bromide (PB). Pyridostigmine bromide and its alkaline-induced degradation product were separated on silica gel HPTLC F254 plates using methanol–ethyl acetate–triethyl amine–glacial acetic acid (9:1:0.5:0.05 by volume) as the developing system followed by scanning of the separated bands at 270 nm over a concentration range of 2–10 μg band−1 with mean percentage recoveries of 99.84% (SD 1.384). The proposed method was successfully applied to the analysis of pyridostigmine bromide both in bulk powder and in pharmaceutical formulation without interference from other dosage form additives. The results obtained by the proposed method were statistically compared with those obtained by the reported HPLC method with no significant difference regarding both accuracy and precision, indicating the ability of the proposed method to be reliable and suitable for routine analysis of a drug product.
Authors:Katarzyna Stachowiak-Szymczak and Paweł Korpal
Simultaneous interpreting is a cognitively demanding task, based on performing several activities concurrently (Gile 1995; Seeber 2011). While multitasking itself is challenging, there are numerous tasks which make interpreting even more difficult, such as rendering of numbers and proper names, or dealing with a speaker's strong accent (Gile 2009). Among these, number interpreting is cognitively taxing since numerical data cannot be derived from the context and it needs to be rendered in a word-to-word manner (Mazza 2001). In our study, we aimed to examine cognitive load involved in number interpreting and to verify whether access to visual materials in the form of slides increases number interpreting accuracy in simultaneous interpreting performed by professional interpreters (N = 26) and interpreting trainees (N = 22). We used a remote EyeLink 1000+ eye-tracker to measure fixation count, mean fixation duration, and gaze time. The participants interpreted two short speeches from English into Polish, both containing 10 numerals. Slides were provided for one of the presentations. Our results show that novices are characterised by longer fixations and they provide a less accurate interpretation than professional interpreters. In addition, access to slides increases number interpreting accuracy. The results obtained might be a valuable contribution to studies on visual processing in simultaneous interpreting, number interpreting as a competence, as well as interpreter training.
High precision gamma spectrometry measurements have been made on five sets of uranium isotope abundance reference materials for nondestructive assay (NDA). These sets are intended for international safeguards use as primary reference materials for the determination of the235U abundance in homogeneous uranium bulk material by gamma spectrometry. The measurements were made to determine the count rate uniformity of the235U 185.7 keV gamma-ray as well as the235U isotope abundance for each sample. Since the samples were packaged such that the U3O8 is infinitely thick for the 185.7 keV gamma-ray, the measured count rate was not dependent on the material density. In addition, the activity observed by the detector was collimated to simulate calibration conditions used to measure bulk material in the field. The sample-to-sample variations observed within the 5 sets of samples ranged between 0.005–0.11% (1s) with standard deviations of the mean ranging from 0.01–0.02%. This observed variation appears to be due predominantly to counting statistics and not to material inhomogeneity and/or packaging. The results of this study indicate that accuracy of235U determinations via gamma spectrometry, in the range of few hundredths of a percent (2), is achievable. The main requirement for achieving this level of accuracy is a set of standards whose235U isotope abundances are known to within 0.01% (2).