Metrology Laboratory Research Articles

A scanning device for VIS–NIR multispectral imaging of paintings

We present a scanning device for multispectral imaging of paintings in the 380–2300 nm spectral range (32 VIS+14 NIR bands). The system is based on contact-less and single-point measurement of the spectral reflectance factor. Multispectral images are obtained by scanning the painted surface under investigation. At present the VIS and NIR modules work separately due to the lack of synchronization between them. Measurement campaigns were carried out on several paintings in situ and at the INOA Optical Metrology Laboratory located inside the Opificio delle Pietre Dure in Florence. We report herein on the measurements carried out on a few panel and canvas paintings. Multivariate image analyses (MIAs) were performed and the detected images were analysed by means of the conventional principal component analysis (PCA) and the K-nearest-neighbouring cluster analysis (KNN).

Uncertainties in calibration using capacitance diaphragm gauges as reference standard

A study of the uncertainties in calibration using capacitance diaphragm gauges as reference standard in the range from 1000 mbar to 10 −3 mbar is presented. The contributions to the expanded uncertainty are: (i) Uncertainty from the calibration certify of the reference standard; (ii) Long-term stability or shift; (iii) Uncertainties inherent to the reference standard; (iv) Uncertainties derived from the calibration chamber; and (v) Uncertainties derived from the calibration procedure. These contributions have been determined for four reference standard capacitance diaphragm gauges of 1.3 mbar, 13 mbar, 130 mbar and 1300 mbar full scale used in routine calibration. Long-term stability or shift jointly with the uncertainty displayed in the calibration certifies issued by a National Metrological Laboratory are the main contributions to the expanded uncertainty. Values of the shift for each of the reference standard for a period of several years are presented and discussed. Best-expanded uncertainties obtained from calibration of a gauge of similar characteristics to the reference standards are: 10 −3–1 mbar 4–0.2% of the reading 1–13 mbar 0.2% of the reading 13–130 mbar 0.2–0.08% of the reading 130–1300 mbar 0.2–0.06% of the reading

Optimization of a coincidence system using plastic scintillators in 4 π geometry

Improvements recently developed at the Nuclear Metrology Laboratory of IPEN-CNEN/SP in São Paulo were performed in order to increase the detector efficiency of a 4 πβ− γ coincidence primary system using plastic scintillators in 4 π geometry. Measurements were undertaken and compared to the original system and Monte Carlo simulations of the extrapolation curves were calculated for this new system and compared to experimental results. For this purpose, the code Penelope was applied for calculating response functions for each detector and the code Esquema, developed at LMN, was used for simulating the decay scheme processes.

Standardization of 241Am, 124Sb and 131I by live-timed anti-coincidence counting with extending dead time

The National Metrology Laboratory for Ionizing Radiation (LNMRI)/Brazil has implemented a live-timed anti-coincidence system with extending dead time to complement the existing systems in its Radionuclide Laboratory for activity measurements of radioactive sources. In this new system, the proportional counter has been replaced by a liquid-scintillation-counter for alpha and beta detection. In order to test the performance of the new system, radioactive solutions of 131I, 124Sb and 241Am have been standardized. In this work the measurement method, the results and the associated uncertainties are described and discussed.

Measurement of conversion coefficients between free in air kerma and personal dose equivalent for diagnostic X-ray beams

Conversion coefficients between free in air kerma and personal dose equivalent were experimentally determined for the diagnostic X-ray qualities recommended by the International Electrotechnical Commission (IEC) for primary beams (RQR) and three RQA. Harshaw LiF-100H thermoluminescent dosemeters (TLD) were used for measurements after being calibrated against an ionization chamber traceable to the National Metrology Laboratory. A 300 mm × 300 mm × 150 mm polymethilmethacrylate (PMMA) slab phantom was used for deep-dose measurements. The dosemeters were placed in the central axis of the X-ray beam at five different depths in the phantom (5, 10, 15, 25 and 35 mm) upstream the beam direction. The typical combined standard uncertainty of conversion coefficient value was 12%.

Report on a comparison of pressure standards in the range 10 MPa to 100 MPa

A comparison in the hydraulic pressure range between 10 MPa and 100 MPa was undertaken as EUROMET Project 389. The comparison was originally between five national metrology laboratories but was subsequently expanded to include a further ten participants. The pilot laboratory was the National Physical Laboratory. This report presents the results obtained by each laboratory for the effective area of the piston–cylinder assembly used in the comparison. The results of all participants were found to be consistent with each other and with the calculated reference value, within their claimed uncertainties, at all pressures. The results are therefore considered to be very satisfactory.Main text.To reach the main text of this Paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Final report on EUROMET supplementary comparison EUROMET.L-S12: Calibration of gauge blocks by mechanical comparison

At its meeting in Prague in October 1999, the EUROMET Technical Committee for Length, TC-L, decided upon a supplementary comparison on gauge block measurements, numbered EUROMET.L-S12, with the National Metrology Laboratory Ireland (NML) as the pilot laboratory. NPL, UK, agreed to act as co-pilot and linking laboratory to the corresponding key comparison, EUROMET.L-K1, by making both mechanical comparison and interferometric measurements. The comparison was subsequently registered as EUROMET project 601.This report describes the results of measurements of eight gauge blocks at thirteen European national metrology institutes. This comparison was carried out during the period from April 2001 to September 2002.The primary measurement quantity was the deviation of the central length of the gauge block from its nominal length, as defined in ISO 3650. The central length was determined by mechanical comparison against the laboratory reference gauge blocks using an appropriate mechanical comparator. Where possible, the participants also determined the variation in length across the surface of each gauge by undertaking measurements at five points on the surface of each gauge against the central length of the laboratory reference gauge block.The results obtained show a good overall agreement of measurement results with the calculated mean values. The uncertainties claimed in the CMC tables are broadly in line with those achieved in this supplementary comparison.Main text.To reach the main text of this paper, click on Final Report.Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Bilateral comparison of 10 V standards between the NML (Ireland) and the BIPM, May to June 2008 (part of the ongoing BIPM key comparison BIPM.EM-K11.b)

As a part of the ongoing BIPM key comparison BIPM.EM-K11.b, a comparison of the 10 V voltage reference standards of the BIPM and the National Metrology Laboratory (NML), Dublin, Ireland, was carried out from May to June 2008. Two BIPM Zener diode-based travelling standards (Fluke 732B), were transported by freight to NML.At the BIPM, the traveling standards were calibrated with the Josephson Voltage Standard. Results of all measurements were corrected for the dependence of the output voltages on ambient temperature and pressure. The NML measurements were carried out by comparison with the mean of the NML voltage standard.A least-squares method is used to reduce the data, which comprise the measured voltage differences and the predicted output EMFs of the reference devices.The final result of the comparison is presented as the difference between the value assigned to a 10 V standard by the NML, at the NML, UNML, and that assigned by the BIPM, at the BIPM, UBIPM, which for the reference date is:UNML − UBIPM = −0.56 µV; uc = 1.32 µV on 2008/05/28,where uc is the standard uncertainty associated with the measured difference, including the uncertainty of the representation of the volt at the BIPM, the uncertainty of the representation of the volt at NML, and the uncertainty related to the comparison.This satisfactory result shows that the voltage standards maintained by the KRISS and the BIPM were equivalent, within their stated expanded uncertainties, on the mean date of the comparison.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Assurance of the traceability chain for 131I measurement

The paper presents some recent results of the Radionuclide Metrology Laboratory (RML) from IFIN-HH, concerning the assurance of the international traceability for the measurement of 131I solution aimed to continue the national chain for nuclear medicine applications in Romania. The following sequences of the traceability are presented: the absolute standardization of solution by the 4πβ-γ coincidence, efficiency extrapolation method and participation in the BIPM.RI(II)-K1.I-131 key comparison; and recalibration of the CENTRONIC IG12/20A ionization chamber secondary standard. The participation in the IAEA/SSDL (SSRL) 131I comparison is also presented.

Focus on nanoscience and nanotechnology

Focus on nanoscience and nanotechnology

Monte Carlo simulation of β–γ coincidence system using plastic scintillators in 4 π geometry

A modified version of a Monte Carlo code called Esquema, developed at the Nuclear Metrology Laboratory in IPEN, São Paulo, Brazil, has been applied for simulating a 4 πβ(PS)–γ coincidence system designed for primary radionuclide standardisation. This system consists of a plastic scintillator in 4 π geometry, for alpha or electron detection, coupled to a NaI(Tl) counter for gamma-ray detection. The response curves for monoenergetic electrons and photons have been calculated previously by Penelope code and applied as input data to code Esquema. The latter code simulates all the disintegration processes, from the precursor nucleus to the ground state of the daughter radionuclide. As a result, the curve between the observed disintegration rate as a function of the beta efficiency parameter can be simulated. A least-squares fit between the experimental activity values and the Monte Carlo calculation provided the actual radioactive source activity, without need of conventional extrapolation procedures. Application of this methodology to 60Co and 133Ba radioactive sources is presented and showed results in good agreement with a conventional proportional counter 4 πβ(PC)–γ coincidence system.

Calculation of calibration figures and the volume correction factors for 90Y, 125I, 131I and 177Lu radionuclides based on Monte-Carlo ionization chamber simulation method

Many metrology laboratories are dealing with activity measurements of different radionuclides with special interest in nuclear medicine as well as in radiopharmaceutical industry. In improving the accuracy of radionuclide activity measurements, a key role plays the calculation of calibration figures and the volume correction factors for the radionuclide under study. It is well known that the chamber calibration factors depend on the measurement geometry including the volume of the source and the type of the measurement vessel. In this work, the activity standards in the form of radioactive solutions are delivered in sealed Jena glass 5 ml FIOLAX ®-klar ampoule. Calculation of the calibration figures (or efficiencies) for 90Y, 125I, 131I and 177Lu radionuclides on 5 ml ampoule are presented in this paper. Additionally, their appropriate volume correction factors are determined. These calibration figures for the ISOCAL IV pressurized well re-entrant ionization chamber (IC) are pointed out based on the Monte-Carlo (MC) simulation method of such chamber using the PENELOPE-2005 MC computer simulation code. The chamber is filled with nitrogen gas pressurized to approximately 1 MPa. In determining the volume correction factors, the variation of calibration factors versus the mass of radioactive solution filling the 5 ml ampoule glass is investigated. From the point of view that impurity of 177 m Lu isomer is always accompanying the 177Lu radionuclide, for making possible the correction due to presence of this impurity, the calibration factor and the volume correction factors for 177 m Lu are reported as well.

Design of multiple-function long trace profiler

The long trace profiler (LTP) is a useful optical metrology instrument for measuring the figure and slope error of cylindrical aspheres commonly used as synchrotron radiation (SR) optics. A multiple-function LTP (LTP-MF) is developed at the optical metrology laboratories of Brookhaven National Laboratory (BNL) with a goal of increasing the accuracy of the measurement and extending the range of applications to other areas. Characteristics of the LTP-MF are a very compact and lightweight optical head, a large angular test range (±16 mrad), and high accuracy. The LTP-MF can be used in various configurations: as a laboratory-based LTP, as an in situ LTP or penta-prism LTP, as an angle monitor, as a portable LTP, and as a small-radius-of-curvature test instrument. The system configuration, designs of the compact optical head and slide, and analysis of different measurements modes and systematic error correction methods are introduced. Preliminary comparison measurements between the LTP-MF and the LTP-II are presented.

Study and realization of a transfer detector based on porous silicon for radiometric measurements

A photodetector of high accuracy has been developed at the “Laboratoire de Métrologie des Rayonnements (L.M.R)—Tunisia” to serve as a transfer detector for optical power measurements in the visible spectral range, i.e. wavelength from 400 to 800 nm. The originality of the work, comparing with other ones, consists of realizing a pn + junction with a n + porous silicon layer on the front face and a zinc oxide (ZnO) film as a transparent electrode above the porous layer. This detector's structure permits to the porous silicon layer to trap the incident optical radiation and to reduce the reflection coefficient fluctuations of the front face to a value of about 7%. The uncertainties relating to the spatial response uniformity of the detector and especially in the central area with 5 mm diameter are equal to 0.5–0.7% for vertical and horizontal directions, respectively. The realized photodetector can roughly reach 10 mW of measured optical power. This value represents an earning of one decade comparing with commercial photodiodes that cannot measure optical power beyond 1 mW. The photodetector presents a linearity with a cumulated deviation of a few 10 −4 through more than 4 decades with an uncertainty of 1.5×10 −4 at 1 σ level. The photodetector was also indirectly calibrated with the cryogenic radiometer of the “Institut National de Métrologie (INM)–France” and provides a convenient standard with a relative standard uncertainty of a few 10 −3 at the 1 σ level. This uncertainty is equivalent to commercial transfer detectors used in metrology laboratories.

Investigation of the Air Kerma Response of Spherical Ionization Chambers for Unfolded Pulse Height Distributions of 60Co and 137Cs using the EGS4 Monte Carlo Code

Data required for the determination of the absolute air kerma rate for (60)Co and (137)Cs gamma-rays using spherical cavity chambers were calculated using the EGS4 Monte Carlo system. Mass energy-absorption coefficient ratio and the stopping power ratio were calculated for a 10 cm(3) primary standard graphite-walled ionization chamber from the unfolded energy pulse height distributions of (60)Co and (137)Cs sources. Wall correction factors and non-uniformity correction factors for two graphite and one air equivalent plastic walled ionization chambers were also calculated with EGS4 code. The wall correction factors were compared with those determined by an experimental extrapolation method. To check the accuracy of the calculations the results were compared with those obtained from other primary standard laboratories such as NIST and NRCC. For a 10 cm(3) graphite ionization chamber, the mass energy-absorption coefficient ratios were 0.99917 for (60)Co and 1.0004 for (137)Cs. The values differed by 0.02-0.05 % for (60)Co and 0.11 % for (137)Cs from those of two laboratories. The stopping power ratios were 0.99984 for (60)Co and 1.0087 for (137)Cs. Comparison with NIST values showed differences of 0.06 % for (60)Co and 0.04 % for (137)Cs. The wall correction factors were obtained and they were different by 0.6-1.1 % for (60)Co and (137)Cs compared to the experimental linear extrapolation method. These values were compared with Monte Carlo derived values from other laboratories. The non-uniformity correction factors were also calculated and they differed from unity, the traditional value used in most standard national metrology laboratories.

Simulation studies on a prototype ionisation chamber for measurement of personal dose equivalent, Hp(10)

A prototype ionisation chamber for direct measurement of the personal dose equivalent, Hp(10), similar to the one developed by the Physikalisch-Technische Bundesantalt (PTB), was designed and constructed by the Metrological Laboratory of Ionizing Radiation (LMRI) of Nuclear and Technological Institute (ITN). Tests already performed have shown that the behaviour of this chamber is very similar to the PTB chamber, mainly the energy dependence for the X-ray radiation qualities of the ISO 4037-1 narrow series N-30, N-40, N-60, N-80, N-100 and N-120 and also for gamma radiation of 137Cs and 60Co. However, the results obtained also show a dependence on the energy and angles of incident radiation and a low magnitude of the electrical response of the ionisation chamber. In order to optimise the performance of the chamber, the LMRI initiated numerical simulation of this ionisation chamber by Monte Carlo method using the MCNPX code.

Gravimetric Calibration of Volumetric Standards with Capacities Exceeding Five Gallon

Recently, the demand for volumetric measurements with greater accuracy and smaller measurement uncertainties has increased dramatically. In response, the metrology laboratories of the Arizona, Main...

The preparation, assay and certification of aqueous ethanol reference solutions

Internationally, certified ethanol reference materials are required to calibrate breathalysers and blood-alcohol measurement instruments. The CSIR National Metrology Laboratory of South Africa provides certified aqueous ethanol solutions with traceability to the SI. Ethanol solutions in the concentration range 10 mg/100 g to 20 g/100 g are prepared gravimetrically by mixing ethanol and reagent quality water. To verify the concentration of the ethanol it is oxidized to acetic acid with potassium dichromate in the presence of sulphuric acid. The unreacted potassium dichromate is back-titrated with sodium thiosulphate. The method utilizes gravimetry and titrimetry, which are both primary methods. This paper addresses aspects of ethanol-certified reference materials that have not been previously published: traceability, stability of unpreserved ethanol solutions, homogeneity, quality control measures and the effect of reproducibility on the measurement uncertainty.

Indirect comparison of the absolute LMR-Tunisia trap pyroelectric detector with the INM-France cryogenic absolute radiometer at 632.8 nm

A trap pyroelectric detector has been developed at the “Laboratoire de Métrologie des Rayonnements (Radiation Metrology Laboratory), LMR” to serve as a Tunisian standard for optical power measurements in the visible and infrared spectral range. This trap detector was indirectly compared with the cryogenic absolute radiometer of the “Institut National de Métrologie (National Institute of Metrology), INM-France” using a silicon photodiode. This comparison was performed at 632.8 nm and at a radiant power level of 350 μW. If the silicon photodiode is assumed to be stable with time, then the two radiometers of different design have been shown to agree to 3 × 10 −3 with an uncertainty of 5 × 10 −3 at the 1σ level.

Calculation of electron deposition in proportional counters

Efficiency extrapolation is a common technique in the standardization of radionuclides by the technique of 4 πβ– γ coincidences. It can be achieved in two ways: adding thin films onto the radioactive source or by electronic discrimination in a pressurized 4 πβ– γ system. The last case is the most extensively used actually in metrology laboratories. There is a need to know the electron energy loss inside the proportional counter as a function of the electron energies and working pressures. Calculations of electron energy loss have been performed for electron energies in a range from a few keV to 2 MeV in a mixture of Ar(90%) CH 4(10%) and for pressures ranging from 100 to 2000 kPa in a 5 cm radius proportional counter. Wall effects, such as electron backscattering, are included in the calculations. Results are provided in the form of graphs and some recommendations are given about the optimal values of the energies that can be used to perform the extrapolation in the standardization of some radionuclides.