1,721,343 research outputs found
Evidence against solar influence on nuclear decay constants
No full textThe hypothesis that proximity to the Sun causes variation of decay constants at permille level has been tested and disproved. Repeated activity measurements of mono-radionuclide sources were performed over periods from 200 days up to four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and are attributable to instabilities in the instrumentation and measurement conditions. The most stable activity measurements of alpha, beta-minus, electron capture, and beta-plus decaying sources set an upper limit of 0.0006% to 0.008% to the amplitude of annual oscillations in the decay rate. Oscillations in phase with Earth's orbital distance to the Sun could not be observed within a 10−6 to 10−5 range of precision. There are also no apparent modulations over periods of weeks or months. Consequently, there is no indication of a natural impediment against sub-permille accuracy in half-life determinations, renormalisation of activity to a distant reference date, application of nuclear dating for archaeology, geo- and cosmochronology, nor in establishing the SI unit becquerel and seeking international equivalence of activity standards. © 2016 The Author
Measurement of absolute γ-ray emission probabilities in the decay of 227Ac in equilibrium with its progeny
No full textThe emission probabilities of γ rays produced in the 227Ac decay series were determined by high-resolution γ-ray spectrometry of sources with standardised activity. The sources were prepared quantitatively on glass discs by drop deposition of a solution with 227Ac in radioactive equilibrium with its daughter nuclides. Their activity was measured by a primary standardisation technique based on alpha-particle counting at a defined low solid angle. Four laboratories performed γ-ray spectrometry and derived absolute γ-ray intensities. Mean values were calculated and compared with literature data and the currently recommended evaluated data. New values on certain γ-ray emission probabilities are proposed. © 2018 The Author
60Co in cast steel matrix: A European interlaboratory comparison for the characterisation of new activity standards for calibration of gamma-ray spectrometers in metallurgy
No full textTwo series of activity standards of 60Co in cast steel matrix, developed for the calibration of gamma-ray spectrometry systems in the metallurgical sector, were characterised using a European interlaboratory comparison among twelve National Metrology Institutes and one international organisation. The first standard, consisting of 14 disc shaped samples, was cast from steel contaminated during production ("originally"), and the second, consisting of 15 similar discs, from artificially-contaminated ("spiked") steel. The reference activity concentrations of 60Co in the cast steel standards were (1.077±0.019) Bq g-1 on 1 January 2013 12h00 UT and (1.483±0.022) Bq g-1 on 1 June 2013 12h00 UT, respectively. © 2016 The Authors
InSiCal – A tool for calculating calibration factors and activity concentrations in in situ gamma spectrometry
No full textIn situ gamma spectrometry is a widely applied analysis technique for the determination of radioactivity levels in soil. Compared to traditional laboratory analysis of soil samples, in situ techniques offer a quick and low-cost way of obtaining accurate results from on-site measurements. However, although the technique is well-known, the dependence of in situ gamma spectrometry on complex and time-consuming calibration procedures as well as in-depth knowledge of the geometric distribution of the source in the ground deters many potential users from employing it in their routine work. Aiming to alleviate this issue, a software tool named InSiCal (In Situ gamma spectrometry Calculator) has been developed to make in situ gamma spectrometry more accessible to both experts and non-experts in the field. This is done by simplifying and streamlining both calibration and activity calculation through a simple and intuitive graphical user interface. Testing in real field conditions show that InSiCal is capable of yielding results which are in very good agreement with soil sample analyses, and that the results may be obtained using different detector types (HPGe, NaI, LaBr and CZT). Overall, InSiCal, provides results which are comparable in accuracy to laboratory measurements, indicating that it fulfills its purpose successfully. © 2017 Elsevier Lt
Interlaboratory comparison on 137Cs activity concentration in fume dust
No full textA comparison was conducted, between 11 European National Metrology Institutes and EC-JRC, on measurement of 137Cs activity concentration in fume dust. As test material an activity standard produced from real contaminated fume dust was used. The standard material consisted of 13 cylindrical samples of compressed fume dust. The material contained 137Cs and 60Co of reference activity concentrations of (9.72±0.10)Bq/g and (0.450±0.018)Bq/g, respectively, for the reference date of 1 June 2013, determined using the comparison results. The organization and results of the intercomparison, as well as the process of obtaining reliable reference values are presented. © 2015 The Authors
A numerical procedure for the preliminary design of a ORC power plants with positive displacement expanders
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Numerical analysis of ground-shotcrete interaction in tunnelling
No full textThe increasingly frequent use of shotcrete as primary support in tunnelling is not always accompanied, at the design stage, by analyses capable of describing its mechanical behaviour. In the first part of this paper the experimentally observed behaviour of shotcrete and its main properties as a supporting material are outlined, together with a critical overview of the general approaches adopted in modelling ground-support interaction in tunnelling. The results of three-dimensional parametric analyses of tunnel excavation and support are then presented. The analyses have been performed in axi-symmetric conditions, assuming an elastic constitutive law characterised by a time-dependent stiffness for the shotcrete. The numerical results are then compared in order to determine the influence of the following factors: constitutive law, strength parameters, tunnel advancement rate, relative ground-support stiffness. In the final part of the paper, simplified techniques are proposed to introduce the main features that emerged from the axi-symmetrical approach in the standard two-dimensional analysis
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