Centre For Metrology Research Articles

Bilateral Comparison of Humidity Standards Between UME and MIKES

In order to assure the quality of dew-point measurements, a bilateral comparison between the National Metrology Institute of Turkey (UME) and the Centre for Metrology and Accreditation (MIKES), Finland, was carried out in 2006. This comparison is registered as EUROMET Project No. 906. Two chilled-mirror hygrometers (MBW 373 and MBW 373H) were used to compare the UME two-pressure humidity generator with the MIKES dew/frost-point generator. An MBW 373 was used in the range from a frost point of −20 °C to a dew point of +20 °C and an MBW 373H in the range from a frost point of −20 °C to a dew point of +60 °C. Dew-point temperature measurements were performed at six dew-point temperatures in the range from a frost point of −20 °C to a dew point of +60 °C at UME and MIKES. According to the results, the mean difference between the laboratories varies from (−0.11 to +0.07) °C over the range. The estimated expanded uncertainty (k = 2) varies from (0.13 to 0.28) °C. A detailed description of the equipment, results and uncertainty analysis is presented in this paper.

MRI study of radiation effect on Fricke gel solutions

The quality control optimization of medical processes that use ionizing radiation in the treatment of diseases like cancer is a key element for patient safety and success of treatment. The major medical application of radiation is radiotherapy, i.e. the delivery of dose levels to well-defined target tissues of a patient with the purpose of eliminating a disease. The need of an accurate tumour-edge definition with the purpose of preserving healthy surrounding tissue demands rigorous radiation treatment planning. Dosimetric methods are used for dose distribution mapping region of interest to assure that the prescribed dose and the irradiated region are correct. The Fricke gel (FXG) is the main dosimeter that supplies visualization of the three-dimensional (3D) dose distribution. In this work the dosimetric characteristics of the modified Fricke dosimeter produced at the Radiation Metrology Centre of the Institute of Energetic and Nuclear Research (IPEN) such as gel concentration dose response dependence, xylenol orange addition influence, dose response between 5 and 50 Gy and signal stability were evaluated by magnetic resonance imaging (MRI). Using the same gel solution, breast simulators (phantoms) were shaped and absorbed dose distributions were imaged by MRI at the Nuclear Resonance Laboratory of the Physics Institute of Sao Paulo University.

Study of [formula omitted] and LiF:Mg,Ti detectors TL response to electron radiation using a SW Solid Water phantom

The TL response to electron-radiation is known to be dependent on the electron energy and the dosimeter thickness, justifying the present study of LiF:Mg,Ti (TLD-100, Harshaw) and CaSO 4 : Dy (developed and produced at the Dosimetric Materials Laboratory of the Radiation Metrology Centre) TL responses to electron radiation using a SW Solid Water phantom. Dosimeters were previously divided in groups according to their individual sensitivities to 60Co gamma-radiation in air and electronic equilibrium conditions. The electron beams of different energies were provided by a Varian Clinac 2100C linear accelerator and the dosimeters were set at the depth of maximum dose of each beam over 5 g / cm 2 of the SW Solid Water phantom made of 30 × 30 cm 2 plates of different thickness. The irradiations with doses ranging from 0.01 to 3.25 Gy delivered at 4 Gy/min were carried out with the electron focus at 100 cm of the phantom surface in a 10 × 10 cm 2 field. The TLD signal was always read in a Harshaw 3500-QS reader 36 h after the irradiation and each value is the average of five readings. The dose–response of both materials presented a linear behavior for doses ranging from 0.05 to 1.25 Gy in all studied energies; however, the CaSO 4 : Dy TL sensitivities are 17.8–21.5 times greater than the ones presented by the LiF:Mg,Ti. The lower detection limit calculated for the LiF:Mg,Ti is 8.49–11.84 times greater than the ones obtained for the CaSO 4 : Dy . Due to these facts, CaSO 4 : Dy dosimeters may constitute one more option for applications in the radiation therapy area in the studied energies and doses, even considering that both CaSO 4 : Dy and LiF:Mg,Ti TL responses were altered by the electron-radiation energy.

Interlaboratory Comparison of Reference Surface Temperature Apparatus at NMIs

During 2001 and 2002, the first international comparison of surface temperature measurements at national metrology institutes (NMIs) was organized under EUROMET Project No 635. The coordinator for this project was the National Office of Measures (OMH) in Hungary. Among the participants were the Swedish National Testing and Research Institute (SP) from Sweden, the Centre for Metrology and Accreditation (MIKES) in Finland, and Justervesenet (JV) in Norway. The comparison showed a need for better apparatus to reduce the differences in the results from the different laboratories. As a result, a new apparatus was designed at SP and MIKES made some changes to their apparatus. To test the new and modified apparatus, SP took the initiative to arrange and coordinate a new comparison. In this recent comparison, measurements were made at temperatures from 50 to 300°C on surfaces of aluminum and stainless steel. The comparison was arranged and performed during 2005 and 2006. Participants in the comparison were OMH, MIKES, RISOE, JV, and SP. The comparison results using the newly developed apparatus show improved agreement with the earlier EUROMET intercomparison, but also indicate a need for a more standardized calibration method and apparatus to be able to perform calibrations in different laboratories with good agreement.

High-accuracy automatic machine vision based calibration of micrometers

The calibration of simple handheld instruments is often more expensive than the price of a new device. Therefore, the amount of manual labour is kept at a minimum in order to keep the price of calibration at a tolerable level. This also means that only a few points of e.g. a length scale can be checked. By using automatic machine vision based systems, the calibration of measurement instruments can be done faster and more thoroughly. In order to study the possibilities of machine vision automation for volume calibration tasks a set-up for micrometer calibration was constructed at Centre for Metrology and Accreditation (MIKES). With the developed automated machine vision system it is possible to check hundreds of points on the scale of a micrometer, giving new insight into error sources of the micrometer screw. The attained uncertainty is at the same level as calibration with gauge blocks according to ISO 3611.

Traceability of Laser Frequency Calibrations at MIKES

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the Practical Realization of the Definition of the Meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers. </para>

An AC Josephson Voltage Standard for AC–DC Transfer-Standard Measurements

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the practical realization of the definition of the meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers

Absolute Frequency Measurement of the R(12) 26-0 and R

A direct phase coherent determination of the absolute frequency of the a15 component in the R(12) 26-0 and b10 component in the R(106) 28-0 transitions in 127I2 at 543 nm has been made at the International Bureau of Weights and Measures. Lasers from the Czech Metrology Institute (Czech Republic), the National Institute of Metrology (China), the Centro Nacional de Metrologia (Mexico), the Standards, Productivity and Innovation Board (Singapore), the Centre for Metrology and Accreditation (Finland), the Danish Institute of Fundamental Metrology (Denmark), the National Physical Laboratory (U.K.), and the International Bureau of Weights and Measures took part. The mean frequency values found are f(a15)=551579856480.4 kHz, uc=4.8 kHz and f(b10)=551580162397.1 kHz, uc=4.6 kHz for the current group of lasers, where uc is the combined standard uncertainty. This constitutes a 30-fold improvement in accuracy for this radiation, which is recommended for the realization of the definition of the meter. If only lasers equipped with an iodine cell temperature control are considered, the group of lasers shows a dispersion of 7 kHz. This value is indicative of the level of reproducibility that can be expected at present for this type of standard

Final report on CIPM key comparison CCM.D-K1: density measurements of a silicon sphere

This report describes the results on a CIPM key comparison of solid density measurements, which was carried out through July 2001 to May 2003. This CIPM key comparison, designated as CCM.D-K1, was coordinated by the National Metrology Institute of Japan (NMIJ, Japan), Swiss Federal Office of Metrology and Accreditation (METAS, Switzerland) and National Research Council Canada (NRC, Canada). These three national metrology institutes (NMIs) formed a pilot group to determine the technical protocol for this key comparison. A total of eight NMIs, namely NMIJ, Physikalisch-Technische Bundesanstalt (PTB, Germany), Istituto di Metrologia 'G Colonnetti' (IMGC, Italy), Korea Research Institute of Standards and Science (KRISS, Korea), METAS, NRC, Centro Español de Metrologia (CEM, Spain) and National Center of Metrology (CENAM, Mexico), participated in this key comparison. A 1 kg single-crystal silicon sphere, prepared by NMIJ, was circulated to each of the NMIs as a travelling standard. Each NMI determined the mass, volume and density of the travelling standard with respect to the mass standard and solid density standard of each NMI by mass measurement and hydrostatic weighing. The reference value of the density was determined with a relative expanded uncertainty of 2.9 × 10-7. When the degrees of equivalence were evaluated by differences from the reference value, the differences for the mass, volume and density were almost equal to or less than expanded uncertainties of the differences, showing a good equivalence of the capabilities for the solid density measurement at the participating NMIs.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).

The experimental investigation of the neutron energy response of the thin ST-401 scintillator

Using the 5SDH-2 Accelerator at the Radiation Metrology Center of CIAE, the experiment of neutron energy response of the thin ST-401 scintillator has been performed. Two T(p,n)3 He and D(d,n)3He reactions are chosen for generating the neutrons. The neutron beam is collimated with the multiplex shielding system. The source intensity is monitored by the proportional counter or semiconductor proton recoil telescope. The neutron response curves of ST-401 scintillators with thickness from 0.16mm to 2.00mm are measured versus neutron energy. The uncertainties of experimental results are discussed in detail. The results show that the sensitivity increases with the scintillator thickness, and for the same thickness, the slope of energy response curve does not change greatly with the increase of neutron energy.

Comparison of the primary low gas flow standards between MIKES and METAS

Abstract At Centre for Metrology and Accreditation (MIKES), a primary calibration system for gas mass flows between 0.42 mg/s and 625 mg/s is based on dynamic weighing providing traceability directly to the national mass and time standards. To evaluate the agreement of the system with a volumetric primary calibrator, the international comparison between MIKES and the Swiss Federal Office of Metrology and Accreditation (METAS, Switzerland) was carried out. At METAS, the primary low gas flow standard provides traceability to the Swiss national measurement standards for length and time. The results of the comparison showed that the two systems do not deviate more than ±0.15% in the mass flow range 0.42–625 mg/s.

Results on the effective area of the FPG-type digital piston manometer of MIKES

The Centre for Metrology and Accreditation (MIKES) has been using a new type of a digital piston manometer (force-balanced piston gauge (FPG)) since 2001. The instrument was developed by DH Instruments Inc., USA. Determination of the effective area was an essential part in validating the FPG in MIKES. One of the big advantages of the FPG is the fact that a conventional pressure balance can be used to determine the effective area. However, the measurement is not straightforward due to the lubrication gas flow in the FPG.The effective area of the MIKES FPG has now been determined several times in the gauge mode by MIKES, once by NMi-VSL, The Netherlands, once by SP, Sweden, and twice by the manufacturer. Measurements in absolute mode have been made using the mercury column manometer of the Physikalisch-Technische Bundesanstalt, Germany.The measurement methods and the results are described in the paper. The results of measurements in MIKES from 2001 to 2004 illustrate the long-term stability and reproducibility of the instrument.

Metrological Provision for Measuring Electromagnetic Properties of Radio Engineering Materials at HF and UHF

The system of metrological provisions for measuring electromagnetic properties of materials at HF and UHF within Russia, and particularly within SNIIM, is considered. The main technical characteristics of domestic standards for measuring the electromagnetic properties of materials are provided and ways for further improvement of metrological provisions for these forms of measurement at the national metrological centers in Russia are discussed.

Comparisons to establish a force-balanced piston gauge and a spinning rotor gauge as the new measurement standards of MIKES

Centre for Metrology and Accreditation (MIKES) has worked towards expanding its calibration capabilities in the absolute pressure range downwards from 0.2 Pa and lowering measurement uncertainties in the range <10 kPa using a force-balanced piston gauge (FPG) and a spinning rotor gauge (SRG). MIKES was the first national pressure laboratory to purchase a novel type of piston manometer, FPG, developed by DH Instruments Inc., USA. The effective area of the FPG was at first determined at MIKES by a comparison with a conventional pressure balance. The result was confirmed in comparisons in the same pressure range with two other laboratories, Swedish National Testing and Research Institute (SP), Sweden and Institute for Metrology and Technology—Van Swinden Laboratorium (NMi-VSL), Netherlands. Next a direct comparison with the mercury column manometer of Physikalisch-Technische Bundesanstalt (PTB), Germany in the absolute pressure range from 1 to 15 kPa was carried out. Use of the FPG for calibration of capacitance diaphragm gauges (CDGs) is also presented. MIKES now uses two SRGs as reference standards, manufactured by MKS Instruments, Inc., USA. A comparison of SRGs in the range from 0.1 to 5 Pa between MIKES, SP and Vaisala Oyj accredited laboratory was performed in 2001–2002.

Upgrading Radiofrequency Electromagnetic Field Standards. Part 2

The stages are considered in incorporating the radio frequency range in electromagnetic field parameter standards. The problems then involved are considered, together with the methods of solution and results obtained. The history of electromagnetic field standards is closely related to research in two metrological centers: VNIIFTRI and NIST.

Results from international comparisons at the bipm providing a world-wide reference network of /sup 127/ I/sub 2/ stabilized frequency-doubled nd:yag lasers

Frequency comparisons have been carried out between iodine-stabilized Nd:YAG lasers from the Bureau International des Poids et Mesures, the Bureau National de Metrologie-Institut National de Metrologie, the Czech Metrology Institute, the Centre for Metrology and Accreditation, and the National Metrology Institute of Japan/National Institute of Advanced Industrial Science and Technology. The comparison data of these lasers can now be linked to the results of recent absolute frequency measurements of lasers from different institutes.

Comparison of 127I2-stabilized frequency-doubled Nd:YAG lasers at the Bureau International des Poids et Mesures.

A frequency comparison was carried out between iodine-stabilized Nd:YAG lasers at 532 nm from the Bureau International des Poids et Mesures, the Centre for Metrology and Accreditation, the Czech Metrology Institute, and the Bureau National de Métrologie-Institut National de Métrologie. The frequency differences between lasers, as well as the frequency reproducibility of each system,were investigated. Pressure-, modulation-, and power-induced shifts were studied. A frequency dispersion (1 sigma) of 3.5 kHz (6.2 x 10(-12) in relative terms) with an average reproducibility for each laser of the order of 0.4 kHz (7.1 x 10(-13) in relative terms) was observed over the duration of the comparison. Relative stabilities better than 1 x 10(13) at 1 s were demonstrated for the third-harmonic systems.

Upgrading Radio-Frequency Electromagnetic Field Standards. Part 1

Stages are considered in incorporating the radio-frequency range in setting up standards for electromagnetic field parameters. The problems involved are discussed, together with methods and results from resolving them. The history of electromagnetic field standards is closely related to researches in two metrological centers: VNIIFTRI and NIST.

A comparison of humidity standards at seven European national standards laboratories

Generator systems realizing a dew-point temperature scale were compared using a chilled-mirror hygrometer. The comparison was carried out by the laboratories maintaining the national standards for humidity in Denmark, Finland, Poland, the Russian Federation, Switzerland, Turkey and the United Kingdom. The Centre for Metrology and Accreditation (MIKES, Finland) co-ordinated the project and acted as the pilot laboratory. The project was carried out in several sub-loops to produce information about the stability of the transfer standard. To analyse the results, the comparison reference value (CRV) was calculated at each measurement point using a cluster method. The CRV was then compared with the results obtained by the participants and normalized errors (En) were calculated. Most of the results show good agreement. The measurements at the METAS, UME and VNIIM did not cover the whole range of the project.

Preliminary Monte Carlo calculation of the conductance of the aperture of a pressure calibration system in the UHV range

The conductance of apertures of pressure calibration systems, based on dynamic reduction of pressure, plays a crucial role in the determination of the uncertainties of the calibrated pressure. In this contribution, we have developed a computer program to perform a Monte Carlo calculation of the conductance of a pressure calibration system installed in the Spanish Metrology Centre (CEM). Firstly, we have compared several pseudo random generators, to check if they are biased in the range of numbers we will use. Afterwards, we have calculated the conductance of simple geometrical systems such as cylinders and frustums of a cone to compare with already published data, finding very accurate results, within estimated uncertainties. Finally, we have obtained the conductance of the aperture, assuming revolution symmetry and a cosine distribution of velocity directions.