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SUSANS with polarized neutrons
No full textSuper Ultra-Small Angle Neutron Scattering (SUSANS) studies over wave vector transfers of 10(-4) nm(-1) to 10(-3) nm(-1) afford information on micrometer-size agglomerates in samples. Using a right-angled magnetic air prism, we have achieved a separation of approximate to 10 arcsec between approximate to 2 arcsec wide up- and down-spin peaks of 0.54 nm neutrons. The SUSANS instrument has thus been equipped with the polarized neutron option. The samples are placed in a uniform vertical field of 8.8 x 10(4) A/m (1.1 kOe). Several magnetic alloy ribbon samples broaden the up- spin neutron peak significantly over the +/- 1.3 x 10(-3) nm(-1) range, while leaving the down-spin peak essentially unaltered. Fourier transforms of these SUSANS spectra corrected for the instrument resolution, yield micrometer-range pair distribution functions for up- and down-spin neutrons as well as the nuclear and magnetic scattering length density distributions in the samples
Slip correction measurements of certified PSL nanoparticles using a nanometer differential mobility analyzer (nano-DMA) for Knudsen number from 0.5 to 83
No full textThe slip correction factor has been investigated at reduced pressures and high Knudsen number using polystyrene latex (PSL) particles. Nano-differential mobility analyzers ( NDMA) were used in determining the slip correction factor by measuring the electrical mobility of 100.7 nm, 269 nm, and 19.90 nm particles as a function of pressure. The aerosol was generated via electrospray to avoid multiplets for the 19.90 nm particles and to reduce the contaminant residue on the particle surface. System pressure was varied down to 8.27 kPa, enabling slip correction measurements for Knudsen numbers as large as 83. A condensation particle counter was modified for low pressure application. The slip correction factor obtained for the three particle sizes is fitted well by the equation: C = 1 + Kn (alpha + beta exp( -gamma/Kn)), with alpha = 1.165, beta = 0.483, and gamma = 0.997. The first quantitative uncertainty analysis for slip correction measurements was carried out. The expanded relative uncertainty (95% confidence interval) in measuring slip correction factor was about 2% for the 100.7 nm SRM particles, about 3% for the 19.90 nm PSL particles, and about 2.5% for the 269 nm SRM particles. The major sources of uncertainty are the diameter of particles, the geometric constant associated with NDMA, and the voltage
Standard model treatment of the radiative corrections to neutron beta-decay
No full textStarting with the Standard Model electroweak Lagrangian, the radiative corrections to neutron beta-decay are obtained. Nucleon compositeness is considered by appropriate parameterization of the nucleon weak transition current and electromagnetic form factors
The T-Odd R and D correlations in beta decay
No full textWe review and discuss the time-reversal-odd R and D correlations in neutron and nuclear beta decay
Johanna 'Anneke' M.H. Levelt Sengers
No full textJohanna Maria Henrica (Anneke) Levelt Sengers was a physicist at the National Institute of Standards and Technology from 1963-1994. She specialized in critical phenomena in fluids and fluid mixtures; from theory to experiment to the creation of databases for practical applications.
In 2000 she was inducted in the NIST Gallery of Distinguished Scientists, Engineers, and Administrators, “For elucidation of the critical behavior and thermophysical properties of industrially important fluids and fluid mixtures”
Education:
University of Amsterdam: BSc, 1950; MSc, 1954; PhD (Physics), 1958
Positions at NIST:
Research Physicist
Group Leader, Thermophysics Division, National Engineering Laboratory
Senior NBS Fellow
Post-retirement: Fellow Emeritus, Physical and Chemical Properties Division, Chemical Science and Technology Laboratory
Honors:
U.S. Department of Commerce: Silver Medal, 1972, Gold Medal, 1978
NBS Condon Award, 1975
Interagency Committee for Women in Science and Engineering WISE Lifetime Achievement Award, 1985
Federal Republic of Germany Alexander von Humboldt Research Award, 1991
Delft University of Technology, ScD (Honorary), 1992
Elected to National Academy of Sciences and National Academy of Engineering
Elected to Sigma X
(Transcript) Oral history interview of Peter L. M. Heydemann, May 4, 2005 / with David Lide, Jack Colwell, Ralph Hudson, Walter Leight, Hans Oser and Harriet Hassler
No full textSimulation of charged particle trajectories in the neutron decay correlation experiment abBA
No full textThe proposed neutron decay correlation experiment, abBA, will directly detect the direction of emission of decay protons and electrons as well as providing spectroscopic information for both particles. In order to provide this information, the abBA experiment incorporates spatially varying electric and magnetic fields. We report on detailed simulations of the decay particle trajectories in order to assess the impact of various systematic effects on the experimental observables. These include among others; adiabaticity of particle orbits, tracking of orbits, reversal of low energy protons due to inhomogeneous electric field, and accuracy of proton time of flight measurements. Several simulation methods were used including commercial software (Simion), custom software, as well as analytical tools based on the use of adiabatic invariants. Our results indicate that the proposed field geometry of the abBA spectrometer will be substantially immune to most systematic effects and that transport calculations using adiabatic invariants agree well with solution of the full equations of motion
Search for time reversal violating effects: R-Correlation measurement in neutron decay
No full textAn experiment aiming at the simultaneous determination of both transversal polarization components of electrons emitted in the decay of free neutrons begins data taking using the polarized cold neutron beam (FUNSPIN) from the Swiss Neutron Spallation Source (SINQ) at the Paul-Scherrer Institute, Villigen. A non-zero value of R due to the e(-) polarization component, which is perpendicular to the plane spanned by the spin of the decaying neutron and the electron momentum, would signal a violation of time reversal symmetry and thus physics beyond the Standard Model. Present status of the project and the results from analysis of the first data sample will be discussed
Bayesian approach to assessing uncertainty and calculating a reference value in key comparison experiments
No full textInternational experiments called Key Comparisons pose an interesting statistical problem, the estimation of a quantity called a Reference Value. There are many possible forms that this estimator can take. Recently, this topic has received much international attention. In this paper, it is argued that a fully Bayesian approach to this problem is compatible with the current practice of metrology, and can easily be used to create statistical models which satisfy the varied properties and assumptions of these experiments
Chemistry of silanes: Interfaces in dental polymers and composites
No full textThe performance and service life of glass- or ceramic-filled polymeric composites depend on the nature of their resin, filler and interfacial phases as well as the efficacy of the polymerization process. The synergy that exists between the organic polymer matrix and the usually inorganic reinforcing filler phase is principally mediated by the interfacial/ interphasial phase. This latter phase develops as a result of the dual reactivity of a silane coupling agent, (YRSiX3), a bifunctional molecule capable of reacting with the silanol groups of glass or ceramic fillers via its silane functional group ( - SiX3) to form Si-O-Si-bonds to filler surfaces, and also with the resin phase by graft copolymerization via its Y functional group, usually a methacrylic vinyl group. In this paper, we explore some of the chemistry of organosilanes, especially that of functional organosilanes ( or silane coupling agents as they are commonly known) that are used to mediate interfacial bonding in mineral reinforced polymeric composites. The chemistry of organosilanes can be quite complex involving hydrolytically initiated self-condensation reactions in solvents ( including monomers) that can culminate in polymeric silsesquioxane structures, exchange reactions with hydroxylated or carboxylated monomers to form silyl ethers and esters, as well as the formation of silane derived interfaces by adhesive coupling with siliceous mineral surfaces