1,721,100 research outputs found
Radionuclide Metrology
Get PDFBehind the scenes of the radioanalytical world, there is a small community of radionuclide metrologists who provide the vital tools to convert detection rates into activity values. They perform highly accurate primary standardisations of activity to establish the SI-derived unit becquerel for the most relevant radionuclides, and demonstrate international equivalence of their standards through key comparisons. The trustworthiness of their metrological work crucially depends on painstaking scrutiny of their methods and the elaboration of comprehensive uncertainty budgets. Through meticulous methodology, rigorous data analysis, performance of reference measurements, technological innovation, education and training, and organisation of proficiency tests, they help the user community to achieve confidence in measurements for policy support, science, and trade. The author dedicates the George Hevesy Medal Award 2020 to the current and previous generations of radionuclide metrologists who have devoted their professional lives to this noble endeavour.JRC.G.2 - Standards for Nuclear Safety, Security and Safeguard
Typical uncertainties in alpha-particle spectrometry
No full textAlpha-particle spectrometry is routinely performed with the aim of measuring absolute activities, activity ratios between different alpha-emitting nuclides or decay data such as branching factors, alpha emission probabilities and relative half-lives. It is most commonly performed with ion-implanted silicon detectors. Strong features of the technique are the low background levels that can be achieved due to low sensitivity to other types of radiation, the intrinsic efficiency close to 1 which reduces the efficiency calculations to a geometrical problem and the uniqueness of the energy spectra for each alpha-decaying nuclide. The main challenge is the limitation to the attainable energy resolution, even with thin and homogenous sources, which causes alpha energy peaks to be partially unresolved due to their width and low-energy tailing. The spectral deconvolution often requires fitting of analytical functions to each peak in the alpha spectrum. True coincidence effects between alpha particles and subsequently emitted conversion electrons cause distortions of the alpha spectra which lead to significant changes in the apparent peak area ratios. Optimum energy resolution can only be achieved on very thin sources, which puts constraints on the source preparation techniques. Radiochemical separations may be needed to extract the alpha emitters from voluminous matrices and efficiency tracing is performed by adding in another isotope by known amounts. Typical uncertainty components are discussed by means of some hypothetical examples.JRC.D.4 - Standards for Nuclear Safety, Security and Safeguard
Detection Efficiency Calculation for Photons, Electrons and Positrons in a Well Detector - Part I: Analytical Model
No full textAn analytical model is presented to calculate the total detection efficiency of a well-type radiation detector for photons, electrons and positrons emitted from a radioactive source at an arbitrary position inside the well. The model is well suited to treat a typical set-up with a point source or cylindrical source and vial inside a NaI well detector, with or without lead shield surrounding it. It allows for fast absolute or relative total efficiency calibrations for a wide variety of geometrical configurations and also provides accurate input for the calculation of coincidence summing effects. Depending on its accuracy, it may even be applied in 4pi-gamma counting, a primary standardisation method for activity. Besides an accurate account of photon interactions, precautions are taken to simulate the special case of 511 keV annihilation quanta and to include realistic approximations for the range of (conversion) electrons and beta- and beta+-particles.JRC.D.4 - Isotope measurement
Cascades of Pile-up and Dead Time
No full textCount loss through a cascade of pile-up and dead time is studied. Time interval density distribution functions and throughput factors are presented for counters with a series arrangement of pile-up with extending or non-extending dead time. A counter is considered where an artifcial dead time is imposed on every counted event, in order to control the length and type of dead time. For such system, it is relatively easy to determine an average count loss correction factor via a live-time clock gated by the imposed dead time signal ('live-time mode'), or otherwise to apply a correction factor based on the inversion of the throughput function ('real-time mode'). However, these techniques do not account for additional loss through pulse pile-up. In this work, counting errors associated with neglecting cascade effects are calculated for measurements in live-time and real-time mode.JRC.D.4 - Isotope measurement
An Intiutive Visualisation of Intercomparison Results Applied to the KCDB
No full textA simple and intuitive graphical method is presented for producing a summary overview of experimental results of a common measurand, e.g. in the frame of an intercomparison. The PomPlots display (relative) deviations of individual results from the consensus value on the horizontal axis and (relative) uncertainties on the vertical axis. The z-scores, z = 1, 2 and 3, are represented by diagonal lines, creating the aspect of a pyramidal structure. The most accurate and precise measurement results should be situated close to the top of the pyramid. The plots are used to visualise data from the BIPM key comparison database on primary radioactivity measurements.JRC.D.4 - Isotope measurement
Status of JRC reference measurements of radioactivity to realise the becquerel
Get PDFThe Radionuclide Metrology group of JRC performs reference measurements of activity and nuclear decay characteristics in support of the common measurement system for radioactivity, as stipulated in Art. 8 of the Euratom Treaty. Primary standardisations of activity performed at the JRC and National Metrology Institutes (NMI) are used at a global scale to establish radioactivity measurements in a traceable manner to the SI unit becquerel. To ensure equivalence of national standards, the NMIs and the JRC participate in key comparisons of their primary standardisation measurements of a common mononuclidic solution. The Bureau International des Poids et Mesures (BIPM) in Sèvres (F) issues a report in which the Key Comparison Reference Value (KCRV) is calculated from a mean of the laboratory results, as well as a Degree of Equivalence (DoE) of each participating laboratory to the KCRV. Thus, the SI unit becquerel is established and international equivalence is demonstrated. Recently, the BIPM published final reports on various key comparisons, which validates standardisation work performed earlier at the JRC and other NMIs. This report gives an overview the corresponding key comparison results.JRC.G.2 - Standards for Nuclear Safety, Security and Safeguard
The uncertainty of counting at a defined solid angle
No full textSpecific uncertainty components of counting at a defined solid angle are discussed. It is potentially an extremely accurate technique for primary standardisation of activity of alpha emitters and low-energy X-ray emitters. Owing to its reproducibility, it is very well suited for half-life measurements. Considered sources of uncertainty are 1) source-detector geometry 2) solid angle calculation, 3) energy loss and self-absorption, 4) scattering, 5) detection efficiency. Other sources of uncertainty, such as source weighing, counting, dead time and decay data are common to other standardisation methods. Statistical uncertainty propagation formulas are presented for the solid angle subtended by a circular detector to radioactive sources. Computer simulations were performed to investigate aspects of particle scattering.JRC.D.4 - Standards for Nuclear Safety, Security and Safeguard
Dealing with discontinuities in half-life measurements
No full textThis case study investigates a half-life experiment that reveals a single step-like discontinuity in counting efficiency across repeated activity measurements. Plausible causes for this discrepancy may involve a sudden change in geometrical conditions or a modification in the electronic pulse processing. The primary objective is to assess whether a more precise determination of the half-life can be achieved through a combined fit of the decay constant and two amplitudes over the entire decay curve, as opposed to deriving a mean value from two independent fits on distinct sections of the decay curve. It answers the question whether accuracy is gained by fitting a single half-life value to several decay curves simultaneously. The analysis employs both rigorous and approximate uncertainty formulas for least-squares fits, alongside a methodology based on empirical decomposition of residuals.JRC.G.II.6 - Nuclear Data and Measurement Standard
An Intuitive Visualisation of Intercomparison Results Applied to the KCDB
No full textA simple and intuitive graphical method is presented for producing a summary overview of experimental results of a common measurand, e.g. in the frame of an inter-comparison. The �PomPlots� display (relative) deviations of individual results from the consensus value on the horizontal axis and (relative) uncertainties on the vertical axis. The z-scores, z=1, 2 and 3, are represented by diagonal lines, creating the aspect of a pyramidal structure. The most accurate and precise measurement results should be situated close to the top of the pyramid. The plots are used to visualise data from the BIPM Key comparison Data Base (KCDB) on primary radioactivity measurements.JRC.D.4 - Isotope measurement
Dead Time, Pile-up and Counting Statistics
No full textAn overview is presented on recent progress in the field of nuclear counting statistics; theoretical expressions are shown to predict deviations from Poisson statistics due to non-random count loss in the spectrometer set-up. Frequently encountered misconceptions in the literature and in daily practice are uncovered: the unconditional belief in the general validity of Poisson statistics, the neglect of the dependency of counting statistics on the considered fraction of the pulse spectrum, the mix-up between pulse pile-up and extending dead time, the unawareness of the influence of pile-up rejection on the counting statistics in fixed live-time measurements and also with ‘loss-free counting’. Insight is provided into the statistical properties of spectra taken with ‘loss-free counting’ and ‘zero dead time’ counting, as well as the ‘variance spectrum’ provided with the latter. Uncertainty formulas are also presented for more conventional nuclear spectrometry measurements, with different types of count loss.JRC.D.4 - Isotope measurement
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