Time filter

Source Type

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.

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.

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.

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.

Discover hidden collaborations