Bureau International Des Poids Et Measures Research Articles

Research on the Methods of Performance Monitoring and Evaluation for Active Hydrogen Maserstwo

Active hydrogen maser is the main frequency standard for establishing and maintaining the time scale. It has the characteristics of high short-term stability and low phase noise. At present, it plays an increasingly important role in the international atomic time (TAI) and various local time scales. Firstly, in combination with the internal state parameters of an active hydrogen maser, the correlation between the internal state parameters and the comparison data of a hydrogen maser is analyzed, and a method for the performance monitoring of a hydrogen maser is proposed. Secondly, according to the characteristics of hydrogen maser performance, a method for evaluating the performance of a hydrogen maser is given. The hydrogen maser performance includes mainly two aspects, namely the frequency stability and predictability. The performances of two types of active hydrogen masers (CH1-75 and MHM-2010) are evaluated by this method. The correlation analysis of the atomic clock state parameters and comparison data shows that the state parameter monitoring can effectively predict the variation of the hydrogen maser performance. The evaluation results of atomic clock frequency stability and predictability show that the atomic clock with a higher medium-and-long term frequency stability has a better predictability. There are two methods for the predictability evaluation, one is based on the data published by BIPM (Bureau International des Poids et Measures), and another one is based on the quadratic model. Both methods are consistent with the weights published by BIPM. Therefore, the two methods can be used as a quantitative method to evaluate the predictability of a hydrogen maser.

Characterization study on NIS X-ray beam qualities and its applications

Quality of low and medium energy X-ray beam at the National Institute for Standards (NIS) of Egypt is studied in details in accordance with the recommendations of the Bureau International des Poids et Measures (BIPM) consultative committee for ionizing radiation (CCRI). The Half Value Layer (HVL) at each applied voltage is precisely determined. The setting up for the X-ray tube according to the TRS No. 469 of IAEA is performed. The effective energy of X-ray is determined using Hyper Pure Germanium Detector (HPGD) connected to photon energy spectrometer. The X-ray air Kerma is measured using NIS secondary standard dosimetry system, which is traceable to the SI units through BIPM. A proposed method for non-invasive tube voltage determination by HPGD is performed. Consequently, all X-ray beam quality parameters are extracted and found to be complying with CCRI recommended values for NIS X-ray tube.This work comprised study on the characterization of NIS low and medium energy X-ray as well as the development of the X-ray laboratory to perform its role in calibrations and to supply customers with traceability to SI units. It gave NIS the ability to participate in international measurement comparisons. A PTW quality assurance set for X-ray is calibrated against the studied X-ray beam qualities to fulfill the requirements of customers needs. The absolute air Kerma for medium energy X-ray is determined using a primary standard free air chamber. Two ionization chambers are calibrated and the calibration factors are compared with values obtained at the BIPM.

A simultaneous moving and weighing technique for a watt balance at room temperature

Measurements made with watt balances are paving the way to a new definition of the kilogram based upon a fixed value of the Planck constant. The Bureau International des Poids et Measures (BIPM) are developing a simultaneous moving and weighing variant of the watt balance technique, which requires a superconducting coil to reach its ultimate uncertainty. The BIPM technique has the advantage that it eliminates the requirement for extreme stability in the magnetic field employed by conventional watt balances, but requires cryogenic operation of parts of the balance to achieve a low uncertainty.This paper proposes a simple method, by which the BIPM technique can be made to operate at room temperature with no loss of accuracy. The superconducting coil is replaced by a bifilar coil and the measurement procedure is modified to eliminate any inequality between the two conductors in the bifilar coil. The new technique is not subject to the many secondary sources of uncertainty arising from cryogenic operation.

Long-term comparison of caesium fountain primary frequency standards

There are currently nine caesium fountain primary frequency standards regularly reporting calibrations of International Atomic Time to the Bureau International des Poids et Measures (BIPM). An investigation has been carried out using data from the BIPM publication Circular T to evaluate the frequency differences among these standards and to determine whether these offsets are consistent with the stated uncertainties. The fractional frequency uncertainties of some Cs fountains are now in the range of 4 × 10−16 to 5 × 10−16. The results of this investigation show that the standards agree well with each other. An overall estimate of the caesium frequency is made using the weighted mean of all the fountains.

Standardization and decay data determinations of 125I, 54Mn and 203Hg

The absolute 4 π– βγ coincidence counting has been used to measure the activity concentrations of 54Mn and 203Hg, and the Sum–Peak method was used for 125I. 54Mn and 125I radionuclides have been part of international key-comparisons coordinated by the Bureau International des Poids et Measures (BIPM) in 2003/2004, while 203Hg is part of the traceability programme of the National Laboratory for Ionizing Radiation Metrology (LNMRI)/Brazil. Three different detectors were used for the Sum–Peak method: 3″×3″ NaI(Tl) and 5″×5″ well NaI(Tl) scintillation detectors and a planar germanium detector. Direct measurements were made of the photon emission probabilities of the 35.5-, 834.8- and 279.2-keV γ-rays of 125I, 54Mn and 203Hg to give values of (0.0667±0.0014), (0.9997±0.0055) and (0.8161±0.0005), respectively. The half-lives of 203Hg and 54Mn were also determined by means of a 4 πγ ionization chamber ( 203Hg) and by the reference source method using a HPGe detector ( 54Mn) to give values of (46.639±0.023) days and (312.1±0.9) days, respectively.

Standardization of 192Ir solution at BARC

A radioactive solution of 192Ir was standardized at Bhabha Atomic Research Centre (BARC) under the international intercomparison programme of the Bureau International des Poids et Measures (BIPM) by 4 π β - γ coincidence and 4 π γ counting techniques, which are primary and secondary methods of standardization, respectively. The activity concentration of the 192Ir solution obtained by the efficiency extrapolation technique and as reported to BIPM was 203.15 kBq g −1 with a combined uncertainty of ±0.3%. The activity concentration determined by 4 π γ counting was 202.88 kBq g −1 with a combined uncertainty of ±1.3%. These measurement results are comparable within the uncertainty limits. Detailed uncertainty budget for both the primary and secondary methods are included.

핵심국제비교용 물의 삼중점 셀 제작과 비교 실험 및 불확도 평가

The <TEX>$Comet{\acute{e}}$</TEX> Consultatif de <TEX>$Thermom{\acute{e}}trie$</TEX> (CCT) under the Comete International des Poids et Measures (CIPM) has decided to perform the Key Comparison (KC) for triple point of water cells used as a reference fixed point of thermometry at the 21st meeting held at November 2001, and the Bureau International des Poids et Measures (BIPM) has been nominated as a KC coordinator. According to the KC protocol prepared by BIPM, KRISS performed the KC experiments and evaluate a uncertainty. The temperature difference between two reference cells for the Korea Research Institute of Standards and Science (KRISS) and a test cell for the transfer standard, which is moved to BIPM was 0.024 mK and the combined standard uncertainty evaluated 0.055 mK.

Recent developments in BIPM voltage standard comparisons

The Bureau International des Poids et Measures (BIPM) carries out a number of comparisons of dc voltage standards with National Metrology Institutes (NMIs). These take the form of on-site comparisons of Josephson standards or bilateral comparisons using traveling standards based on Zener diodes. This paper describes some of the new procedures used in both types of comparison and presents some results of five recent BIPM key comparisons.

Results from the fifth international comparison of absolute gravimeters, ICAG'97

The fifth in the series of International Comparisons of Absolute Gravimeters (ICAG) was held at the Bureau International des Poids et Measures (BIPM) in November 1997. Fifteen absolute gravimeters participated in the comparison. The mean gravity value obtained at station A (0.9 m) at the BIPM was found to be 980 925 707.8 µGal with a standard uncertainty of 2.8 µGal. This is consistent with the results obtained in previous comparisons at this site. Conclusions based on the analysis of the present results and proposals for future activities are presented.

Establishing an SI-traceable Copper Concentration in the Candidate Reference Material MURST ISS A1 Antarctic Sediment Using Isotope Dilution Applied as a Primary Method of Measurement

I. PAPADAKIS, P. D. P. TAYLOR and P. DE BIÈVRE, J. Anal. At. Spectrom., 1997, 12, 791 DOI: 10.1039/A700750G

International Intercomparison of Power Standards at 3 GHz (Correspondence)

An international intercomparison of microwave power at 3 GHz has recently been completed. This comparison was initiated at a meeting of the High Frequency Working Group of the Comite Consultatif d'Electricite (CCE) which met at the Bureau International des Poids et Measures (BIPM) in May, 1965. At that time, the U. S. National Bureau of Standards (NBS) was designated as the pilot laboratory. The other laboratories, in the order of their participation, are the following: for Canada, National Research Council (NRC); for the U. S. S.R., All-Union Research Institute of Metrology imeni D. I. Mendeleyev (VNIIM); for the German Democratic Republic, Deutsches Amt fur Messwesen und Warenprufung (DAMW); and for Japan, the Electrotechnical Laboratory (ETL).