Michotte C.,Bureau International des Poids et Mesures BIPM |
Nonis M.,Bureau International des Poids et Mesures BIPM |
Van Rooy M.W.,National Metrology Institute of South Africa NMISA |
Van Staden M.J.,National Metrology Institute of South Africa NMISA |
Lubbe J.,National Metrology Institute of South Africa NMISA
Metrologia | Year: 2017
In 2015, comparisons of activity measurements of 18F and 99mTc using the Transfer Instrument of the International Reference System (SIRTI) took place at the National Metrology Institute of South Africa (NMISA, South Africa). Ampoules containing about 25 kBq of 18F and 99mTc solutions were measured in the SIRTI for more than two half-lives. The NMISA standardized the activity in the ampoules by ionization chamber measurements traceable to 4π(LS)β-γ coincidence measurements. The comparisons, identifiers BIPM.RI(II)-K4.F-18 and BIPM.RI(II)-K4.Tc-99m, are linked to the corresponding BIPM.RI(II)-K1.F-18 and BIPM.RI(II)-K1.Tc-99m comparisons and degrees of equivalence with the respective key comparison reference values have been evaluated.
Bolokang A.S.,University of Johannesburg |
Bolokang A.S.,South African Council for Scientific and Industrial Research |
Phasha M.J.,South African Council for Scientific and Industrial Research |
Oliphant C.,National Metrology Institute of South Africa NMISA |
Motaung D.,South African Council for Scientific and Industrial Research
International Journal of Refractory Metals and Hard Materials | Year: 2011
In the current study, results of the milled and sintered V, W, C, Co powders are presented. Analytical techniques such as SEM equipped with EDS and XRD were used to study microstructure and phase evolution, respectively. In addition to B1 (VW)C solid solution, a rhombohedral V2O3 and new τ-type (Cr23C6) carbide were formed after sintering. The possible formation mechanisms behind detected phases are discussed. It is evident that complete MA process depends strongly on the starting compositions of pure elements, their lattice coherency according to Hume-Rothery rules on crystal structure and atomic size, and enough milling time that provides adequate kinetics. © 2010 Elsevier Ltd. All rights reserved.
Establishing an alternative method for the quantitative analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by comprehensive two dimensional gas chromatography-time-of-flight mass spectrometry for developing countries
De Vos J.,National Metrology Institute of South Africa NMISA |
Gorst-Allman P.,LECO Africa Pty Ltd. |
Rohwer E.,University of Pretoria
Journal of Chromatography A | Year: 2011
Comprehensive Gas Chromatography-Time-of-Flight Mass Spectrometry (GC×GC-TOFMS) methodology has been refined for the analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in samples with different matrices. This is specifically for application in developing countries where access to gas chromatography-high resolution mass spectrometry (GC-HRMS) and highly skilled personnel is limited. The method, using an Rxi-5 Sil MS column in the first dimension (1D) coupled with an Rtx-200 column in the second dimension (2D), was used to quantify PCDDs and PCDFs in different environmental sample matrices. The results were compared with those obtained using GC-HRMS and good agreement was observed. The limit of detection (LOD) for the method (300fg on column for spiked soil samples) was determined using an Rxi-XLB (1D) column coupled with an Rtx-200 column (2D). Preliminary South African sample results are also discussed. Isomer specificity for different tetrachloro dibenzo-p-dioxins (TCDDs) and tetrachloro dibenzofurans (TCDFs) was investigated using a commercial standard. Adequate resolution was achieved. The method as described has great attraction for developing countries being both financially and operationally favourable. © 2011 Elsevier B.V.
Terra O.,National Institute for Standards of Egypt |
Hussein H.,National Institute for Standards of Egypt |
Burger J.,National Metrology Institute of South Africa NMISA
Optik | Year: 2015
The 5S1/2 (F = 3)-5D5/2 (F = 5) two-photon transition of rubidium (85) at 778 nm is an excellent candidate for a high-quality portable frequency standard at the telecommunication region. The interrogation of the two-photon transition requires efficient second harmonic conversion of a laser at 1556 nm. In this work, a comparison is made between the conversion efficiencies of bulk and waveguide periodically polled lithium niobate (PPLN) crystals. Both crystals are doped with 5% from MgO and used to generate frequency doubled light at 778 nm from a fundamental light source operating at 1556 nm. In order to obtain the optimum operating conditions, the frequency doubled power is measured as a function of laser wavelength and crystal temperature. The conversion efficiency of the waveguide PPLN is found to be around two orders of magnitudes larger than that of the bulk PPLN crystal for input powers less than 150 mW. At the end, the generated second harmonic light from both crystals are used to interrogate the two-photon transition in a natural rubidium gas cell. A comparison is made between the fluorescence spectrums resulting from the two-photon transition using second harmonic generated powers from both crystals. © 2015 Elsevier GmbH. All rights reserved.
Nel-Sakharova N.,National Metrology Institute of South Africa NMISA
International Journal of Metrology and Quality Engineering | Year: 2015
Many National Metrology Institutes (NMIs) realise the spectral irradiance scale by obtaining traceability from a cryogenic radiometer through the use of calibrated filter radiometers. The filter radiometers are used to determine the temperature of a high temperature black body which is then used as a reference source, which spectral radiance can be determined from Planck's equation. The uncertainty of the temperature measurement makes the most significant contribution to the uncertainty of realising the spectral irradiance scale. High temperature fixed points (HTFPs), above the copper point, can be used to improve these uncertainties. After more than ten years of research, results obtained on metal-carbon eutectic fixed points by several NMIs, showed that these novel high temperature fixed points could lead to significant improvements in high temperature metrology and could be considered as potential fixed points in a future International Temperature Scale.This paper describes the development and characterisation of selected high temperature metal-carbon fixed points at NMISA. It is demonstrated that these fixed points can be utilised as reproducible, stable reference standards for temperatures above the copper point. © EDP Sciences 2015.
Jonker D.,National Metrology Institute of South Africa NMISA |
Tarnow E.P.,National Metrology Institute of South Africa NMISA
International Journal of Metrology and Quality Engineering | Year: 2014
The National Metrology Institute of South Africa (NMISA) Gas Flow Laboratory provides traceability to the South African Industry for gas flow measurements. A new primary standard for gas flow calibrations was purchased and commissioned. With three flow cells, a flow range of 0.5 mL/min to 50000 mL/min is covered. The main features of this standard are accuracy, speed and convenience. This paper describes the activities of the NMISA Gas Flow Laboratory-a discussion of the primary standard, the validation thereof, calibration methods for client instrumentation, analysis of measurement results and the calculation of measurement uncertainties. © 2014 EDP Sciences .
Greeff P.,National Metrology Institute of South Africa NMISA |
Kruger O.,National Metrology Institute of South Africa NMISA
International Journal of Metrology and Quality Engineering | Year: 2014
One of the main calibration services of African NMIs (National Metrology Institutes) is the measurement of tapes and rules. This is mainly regulated by legal metrology and OIML (International Organisation of Legal Metrology) specifications are therefore referenced. Specifically, OIML R-35 is the standard to which rules or line scales must conform. The accuracy of most African NMIs systems however, cannot prove conformance to this specification. This article will detail the development of a new, cost effective, line scale calibration system, which will have accuracy better than the specification prescribed. The system was locally developed and its design is based on off-the-shelf components and open source software. It is also ready-for-upgrade to an absolute system. The system and details of the line detection algorithm will be presented. © 2014 EDP Sciences.
Botha A.,National Metrology Institute of South Africa NMISA
Geostandards and Geoanalytical Research | Year: 2010
During the past decade the work of ISO/REMCO, the International Organization for Standardization's Technical Committee on Reference Materials, was dedicated to achieving global harmonisation, and true involvement of the member countries. The first major accomplishment was the clarification of the terminology in the definitions for reference material and certified reference material, which were published as an amendment to ISO Guide 30in 2008. The next milestone was the recognition that ISO Guide 34 ('General requirements for the competence of reference material producers') be used in conjunction with ISO/IEC 17025 for the accreditation of reference material producers. The third edition of ISO Guide 34 published in November 2009, clarifies the acceptable procedures for the certification of reference materials. This paper will discuss the role of ISO/REMCO in formalising the procedures for the accreditation of reference material producers and the evolution of the terms reference material and certified reference material. The paper will conclude with a case study, where a primary method in a single laboratory - one of the recognised acceptable metrologically valid procedures according to ISO Guide 34 - was used for the certification of reference materials. The reference materials are South African Reference Material SARM 2 (Syenite), SARM 3 (Lujavrite) and SARM 4 (Norite) from the suite of six NIMROCs that were originally certified by the Council for Mineral Technology (MINTEK) in South Africa in the 1970s. © 2010 The Author. Geostandards and Geoanalytical Research © 2010 International Association of Geoanalysts.
Ejigu E.K.,National Metrology Institute of South Africa NMISA |
Liedberg H.G.,National Metrology Institute of South Africa NMISA
AIP Conference Proceedings | Year: 2013
A variable-temperature blackbody (VTBB) is used to calibrate an infrared radiation thermometer (pyrometer). The effective emissivity (ε eff) of a VTBB is dependent on temperature and wavelength other than the geometry of the VTBB. In the calibration process the effective emissivity is often assumed to be constant within the wavelength and temperature range. There are practical situations where the sensitivity of the effective emissivity needs to be known and correction has to be applied. We present a method using a genetic algorithm to investigate the sensitivity of the effective emissivity to wavelength and temperature variation. Two matlab® programs are generated: the first to model the radiance temperature calculation and the second to connect the model to the genetic algorithm optimization toolbox. The effective emissivity parameter is taken as a chromosome and optimized at each wavelength and temperature point. The difference between the contact temperature (reading from a platinum resistance thermometer or liquid in glass thermometer) and radiance temperature (calculated from the εeff values) is used as an objective function where merit values are calculated and best fit εeff values selected. The best fit εeff values obtained as a solution show how sensitive they are to temperature and wavelength parameter variation. Uncertainty components that arise from wavelength and temperature variation are determined based on the sensitivity analysis. Numerical examples are considered for illustration. © 2013 AIP Publishing LLC.
Ben Salem A.,University of Carthage |
Cherif R.,University of Carthage |
Zghal M.,University of Carthage |
Burger J.,National Metrology Institute of South Africa NMISA
Progress in Electromagnetics Research Symposium | Year: 2011
We report on numerical and experimental studies of supercontinuum (SC) generation in a silica-based nonlinear polarization-maintaining photonic crystal fiber (PM-PCF). The optical properties of the fundamental mode of the PM-PCF were numerically determined in terms of birefringence, chromatic dispersion and nonlinear coefficient. The fiber has an air hole diameter of 0.6 μm and a pitch of 1.25 μm exhibiting a nonlinear coefficient of 90km -1W -1 and a high value of birefringence which we found to be equal to 4 · 10 -4 at λ = 820 nm. We also determined the positions of the slow and fast axes of the PM-PCF according to the laboratory frame, using two different techniques based on near and far fields. The SC was generated by coupling ultra-short pulses delivered by a mode-locked femtosecond Ti: Sapphire laser centered at 820nm with a repetition rate of 202MHz at the average power of 20mW and having duration of 56 fs. The generation of over 800nm bandwidth of visible and infrared light on both axes (slow and fast) was observed in the 2-m-long silica-based nonlinear PM-PCF. Finally, the coherence and noise structure of the supercontinua generated in the PM-PCF have been discussed.