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Abstract  

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.

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Abstract  

The precision in measurement of trace level uranium isotopic ratio, i.e., 236U/238U or 234U/238U, on single Faraday detector with narrow dynamic range is very hard to achieve. this is mainly due to the narrow dynamic range of a single detector systems. A significant improvement in mass spectrometric determination of 236U/238U ratio has been achieved by employing an alternate method using a single Faraday detector of narrow dynamic range. The method makes use of the precise measurements of the 236U/234U ratio, 234U/235U ratio and 235U/238U ratio, which are used to calculate the 236U/238U ratio using the equation 236U/238U=236U/234234U/235235U/238U. Despite the fact that correlation of the data tends to increase the uncertainty in the result, our results show a significant improvement, i.e., more than 8 times better precision in measuring the 236U/238U ratio with this method (σ=3.98×10−08) as compared to direct measurement of 236U/238U (σ=3.104×10−07). The method widens the applicability of the single collector system with narrow dynamic range and it will potentially be helpful to improve the precision in the case of the static multi-collector system also. The objective of the present study was to compare the results of the same sample analyzed with the present alternate method and the direct method for precision.

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Abstract  

A non-destructive method has been developed for the precise and accurate determination of Sn in cassiterite ores. Irradiation is performed by means of a 6.6 Ci227Ac−BE isotopic neutron source with a total neutron output of 108 n·sec−1. Samples are pellets pressed from a mixture of cassiterite powder and wax as a binding material. With a 4 hrs analysis time and a relative precision of 0.45%, the new method is faster and at least as precise as any existing destructive chemical method. The accuracy is proved to be better than that of the commonly used iodimetric titration method.

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Abstract  

The disintegration of four radionuclides undergoing electron-capture decay was followed for one to ten half-lives. Least-squares analyses of the gamma-ray counting data using non-linear Taylor differential correction yielded the following half-lives: 7Be, 53.42±0.01 days; 54Mn, 312.6±0.5 days; 83Rb, 86.2±0.1 days and 84Rb, 33.1±0.1 days. These values are consistent with literature data, with comparable or much better precision than most previous determinations.

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Abstract  

Determination of239Pu/233U,241Am/233U and244Cm/233U alpha activity ratios is required when using233U as a tracer for the determination of plutonium, americium and curium by alpha spectrometry. Precision and accuracy in the determination of these alpha activity ratios was evaluated by preparing synthetic mixtures from solutions of enriched isotopes of239Pu,241Am,244Cm and233U. Separate synthetic mixtures were prepared for each of the three alpha activity ratios. The sources from the synthetic mixtures were prepared by direct evaporation method using tetra ethylene glycol /TEG/ as a spreading agent, alpha spectra were recorded by employing solid state silicon surface barrier detectors coupled to a 4 K analyzer and the alpha spectra were evaluated by a method based on the geometric progression decrease for the far tail of the spectrum. Large area detector /i.e. 450 mm2/ was observed to reduce the effect of nonhomogeneous distribution, if any, of the two elements present in the source. Precision and accuracy of about 1% is demonstrated for the determination of239Pu/233U,241Am/233U and244Cm/233U alpha activity ratios using large area silicon surface barrier detector.

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Abstract  

Epithermal neutron activation analysis can usefully be used for simultaneous determination of trace elements in rocks. No chemical seperation is required in this case and consequently the precision may be better. In order to estimate the relative importance of the causes of precision error, we have made an analysis of variance on a set of 18 irradiations: 15 elements have been studied. The precision attained on those analytical results is sufficient to be able to construct geochemical models.

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This paper examines how we might test the continuum theory against the community unit theory. Adherence to one or other of these models without testing is simply an assignment of an extreme prior probability to the preferred option. The question can be rephrased to ask whether, for a set of observations, a single model is adequate or whether a mixture of models would be preferable. To judge between them involves first defining the nature of the model(s) to be fitted in each case and then comparing the complexity and quality of fit. Occam's razor suggests that we should seek the simplest model with adequate fit, with parameters estimated with optimal precision. The simplest comparison of the two theories thus requires only the estimation of the number of clusters for the chosen model(s) of within-cluster variation. If a single cluster is of adequate quality then the continuum model is appropriate, while if several are needed then the community model is preferable for that particular dataset. To establish universal applicability of either model involves investigation of many datasets. There are several ways in which model quality can be assessed, and here I concentrate on the minimal message length principle which is a function of the prior probability of the model and its fit to the observed data, assuming the model to be correct. This principle has been shown to perform well when compared with other possibilities. I first illustrate the procedure for making a choice between models, using a simple model, then examine two alternative formulations of within-cluster models which seem more appropriate, one static, the other dynamic.

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Abstract  

Performance of three commercial gamma-ray spectrometric systems was evaluated for precision and accuracy prior to use in characterization of reference materials. Two of the systems were based on fast processing of the analogue signal from the amplifier (EGG Ortec model 672) using a loss free counting module (Canberra model LFC 599) interfaced to one of two analog-to-digital converters (Canberra models 8713 or 8715). The third system was based on a digital signal processor (Canberra model DSP 9660). Performance of the systems was tested over a range of count rates up to a maximum of 70,000 counts per second (dead time up to 90%) using 60Co and 137Cs sources. Best resolution was achieved with an analogue system with ADC 8713. The analytical results obtained with the digital system show the lowest and well-quantified uncertainty.

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There is no information about the risk to Argentinean livestock of poisoning by exposure to Conium maculatum L. as a result of ingestion of its two most toxic alkaloids, γ -coniceine and coniine. To measure their concentrations in this weed an aqueous sulfuric acid extract of C. maculatum foliage alkaloids was adjusted to pH 9 and extracted exhaustively with chloroform. The partly evaporated chloroform extract was used for TLC detection and quantification of γ -coniceine and coniine by using Dragendorff’s spray reagent to detect the alkaloids and visual comparison of the intensity of the color of the sample spots with that of the spots of the corresponding standards. Regression equations for recoveries ( y ) after different standard additions ( x ) were y = −0.761 + 1.051 x ( r 2 = 0.93; p < 0.0001) for coniine and y = −0.193 + 0.863 x ( r 2 = 0.93; p < 0.0001) for γ -coniceine. Average recoveries were 92.0 ± 3.5% and 82.6 ± 3.9% for coniine and γ -coniceine, respectively. By t -tests on addition and recovery values it was shown that for both equations α = 0 and β = 1 ( p > 0.05), which implies recovery is 100%. Detection limits were 1.7 and 0.7 μg per spot for coniine and γ -coniceine, respectively; the respective quantification limits were 0.8 and 0.6 μg mL −1 . The method is suitable for simple, precise, and accurate TLC analysis of these alkaloids.

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