Scope for replacing the prototype kilogram by an atomic mass unit

The main versions of the redefinition for the international prototype kilogram are examined for best accuracy and transmitting the mass unit. It is concluded that it is most promising to use Avogadro’s number and the atomic mass unit in order to transfer to a new standard for the kilogram, i.e., to introduce an atomic kilogram. __________ Translated from Izmeritel’naya Tekhnika, No. 10, pp. 3–5, October, 2006.     

原子质量的相对论效应和应用

应用相对论理论(Dirac)来计算C、O、S、Se、Te、Sm和Pu原子的相对论和非相对论的电子状态和能量,比较相对论和非相对论的能量差别后得到:如果以O原子的相对论和非相对论能量差为1,则S、Se、Sm和Pu原子的相对论和非相对论能量差分别为17.5、479、6 781和46 166。就钚和氧相比,质量的相对论效应增加46 166倍。Pu的相对论的和非相对论的能量的差占总能量的8.72%,所以对重元素,应用相对论的计算是很必要的。     

Measurement of individual particle atomic composition by aerosol mass spectrometry

Advances in instrumentation used for particle compositional analysis have enabled real-time identification and classification of individual particles. However, precise quantitation of individual particle compositions has been elusive. Here, we demonstrate that real-time quantitative single-particle compositional analysis is possible. This is illustrated for individual particles of sodium chloride (70 nm), ammonium sulfate (70 nm), and silica (40-2000 nm) using a real-time aerosol mass spectrometer. Atomic fractions for major components (> 1% concentration) of individual multicomponent particles have been measured within +/-20% accuracy. Trace element detection limits of 20 ppm are also demonstrated when individual particle compositions are ensemble averaged.     

State primary standard of unit of mass fraction and unit of mass concentration of moisture in solid substances and solid fabricated materials

The structure of the state primary standard of the unit of mass fraction of moisture and the unit of mass concentration of moisture in solid substances and solid fabricated materials is considered and the metrological characteristics of these units are presented.     

Precision measurement of the atomic mass of 6Li using aPenning ion trap mass spectrometer

We have used a cryogenic (4 K) Penning ion trap mass spectrometer to measure the mass ratios of ⁶Li⁺/¹²C ²⁺, ⁶Li⁺/D₃⁺, and D₂⁺/He⁺. We developed techniques to create ions outside of the cryogenic trap environment and to transport them into the trap where a small number (1-10) were confined. The ions' frequencies of oscillation were measured using a high-Q tuned circuit to detect image currents induced in the trap electrodes. The measurements involving ⁶Li⁺ result in a value for the atomic mass of ⁶Li of 6.015 122 795(16) u, with a fractional uncertainty of ±2.7×10^-9 representing a factor of 30 improvement over the published, tabulated value. A measurement of the D₂⁺/He⁺ mass ratio has an uncertainty of ±1.1×10^-9 and is within 0.6×10^-9 of the tabulated value, thus demonstrating that our techniques are reliable     

Contemporary status of the state primary standard of the unit of mass

The results of studies designed to improve the State Primary Standard of the unit of mass are considered. In terms of precision of reproduction and stability, the Russian prototype of the kilogram corresponds to the best world analog. Modern electronic comparators of the mass from the world’s leading firms are introduced into the standard.     

Sampling and analysis of particulate matter by glow discharge atomic emission and mass spectrometries

The direct introduction of particulate matter into glow discharge atomic emission and mass spectrometry sources through a particle beam/momentum separator apparatus is described. Vacuum action through a narrow (0.0625 in. i.d.) stainless steel tube allows the introduction of discrete samples of NIST SRM 1648 urban particulate matter (UPM) and caffeine in powder form. Introduction of "ambient" airborne particulate matter is also possible. Particles passing through the aerodynamic momentum separator impinge on the heated (～200-250 °C) inner surface of the glow discharge plasma volume and are flash-vaporized. The resultant atoms/molecules are subjected to excitation/ionization collisions within the low-pressure (0.5-5 Torr of He or Ar) plasma, producing characteristic photon emission and/or signature ionic species. In this way, atomic emission and mass spectrometry identification of particle constituents is possible. Basic design aspects of the apparatus are presented, and demonstrations of atomic emission detection of the constituents in the NIST SRM illustrate the general characteristics of the approach. Transient atomic emission signals are captured for the introduction of preweighed, discrete samples, with the integrated areas used to construct analytical response curves. Limits of detection using this relatively simple atomic emission system are on the order of tens of nanograms for sample masses of ～50 μg. Mass spectrometric monitoring of introduced caffeine particles and a mixture of polycyclic aromatic hydrocarbons (PAHs) illustrates the ability of the glow discharge plasma to produce high-quality, library (electron impact) searchable mass spectra of molecular species while also yielding isotopic identification of elemental components of the UPM. Limits of detection for Fe in the NIST SRM are on the order of 175 ng of material, equivalent to ～7 ng of analyte Fe. It is believed that the small size, low power consumption, ease of operation, and multimode sampling capabilities (AES/MS) of the particle beam-glow discharge (PB-GD) apparatus hold promise for applications in continuous monitoring and discrete particle sampling.     

Speciation of sodium nitrate and sodium nitrite using kiloelectronvolt energy atomic and polyatomic and megaelectronvolt energy atomic projectiles with secondary ion mass spectrometry

The negative-ion mass spectra produced by kiloelectronvolt energy (CsI)nCs+ (n = 0-2) and megaelectronvolt energy 252Cf fission fragment projectile impacts on NaNO3 and NaNO2 were collected and compared. The mass spectra generated by impacts of the kiloelectronvolt polyatomic primary ions on NaNO3 were markedly different from those derived from the fission fragment impacts, featuring higher relative intensities of nitrate (NO3-) specific secondary ions (those that reflect the sample stoichiometry). The most prominent secondary ion (SI) peaks produced from NaNO3 by the kiloelectronvolt energy projectiles were NO3- and Na(NO3)2-, both of which relate directly back to the chemical composition of the staring material. Likewise, the most prominent peaks produced by the kiloelectronvolt energy polyatomic projectile impacts on NaNO2 were NO2- and Na(NO2)2-. The fission fragment projectiles produced SI spectra from NaNO3 that were dominated by signals characteristic more of NaNO2, indicating that the megaelectronvolt energy ions induce considerable degradation of the nitrate solid. In addition, the fission fragment projectile produced relative negative SI intensity distributions that are remarkably similar to those reported in earlier studies of the use of laser desorption to produce SI signals from NaNO3. Of the projectiles examined in this study, the 20 keV (CsI)Cs+ projectile generated negative-ion mass spectra that best differentiated NaNO3 and NaNO2, primarily by producing a base peak in the NaNO3 spectrum that was unambiguously representative of the original sample stoichiometry.     

Some methods for redefining the unit of mass standard fundamental problems in metrology

Contemporary methods are presented for redefining the unit of mass standard, i.e., the kilogram prototype. The main tendencies in improving these methods in order to reduce the uncertainty of reproducing the unit of mass are discussed. It is noted that the use of precise values of a number of fundamental physical constants, primarily the Avogadro number, is important. __________ Translated from Izmeritel’naya Tekhnika, No. 4, pp. 3–7, April, 2006.     

The production of intense atomic beams

Methods of producing multichannel capillary arrays in various materials for use as atomic beam forming devices are reviewed. The advantages of gas focusing arrays are considered. The theories of the flow of gas through a cylindrical tube are discussed. Completely general numerical and graphical results derived from Zugenmaier's theory are presented. Their use in designing gas beam systems is described. Data are presented in a convenient form for the experimentalist. Comparison of the numerical results with published experimental data is made. It is shown that, for most purposes, a capillary is best operated at an input pressure giving a mean free path which is less than 10% of the tube length. In an array, it is an advantage to have tubes of small diameter. With a focusing array, beam densities of up to 10¹⁴ atoms cm^?3 are predicted when the beam half width is 1°.