X-ray determination of the mean amplitudes of vibration and debye temperatures of some rare earth monochalcogenides

The x-ray diffraction intensities of Bragg reflections have been measured at room temperature for thulium selenide, samarium sulphide, samarium selenide and samarium telluride. On the basis of a common amplitude approximation, the Debye-Waller factor, the mean amplitude of vibration and the Debye temperature have been evaluated. The values of the Debye temperatures and mean amplitudes of vibration are 176±16°K, 0·185 ± 0·017 Å (TmSe), 155 ± 7°K, 0·244 ± 0·012 Å (SmS), 153 ± 14°K, 0·221 ± 0·020 Å (SmSe) and 151 ± 20°K, 0·204 ± 0·027 Å (SmTe).     

Progress with the MPIK/UW-PTMS in Heidelberg

The precise determination of the ³He/³H mass ratio, and hence the tritium ??-decay endpoint energy E ₀, is of relevance for the measurement of the electron anti-neutrino mass performed by the Karlsruhe Tritium Neutrino experiment (KATRIN). By determining this ratio to an uncertainty of 1 part in 10¹¹, systematic errors of E ₀ can be checked in the data analysis of KATRIN. To reach this precision, a Penning Trap Mass Spectrometer was constructed at the University of Washington and has been transferred to the Max Planck Institute for Nuclear Physics in Heidelberg at the end of 2008. Since then it is called MPIK/UW-PTMS. Special design features are the utilization of an external ion source and a double trap configuration. The external Penning ion source efficiently ionizes the helium and tritium gas and can give superior elimination of unwanted ion species compared to the previously utilized in-trap-ionization by electrons from a field-emission point. The design as a double Penning trap allows a faster measurement procedure. This should help to avoid problems resulting from long-term drifts in the experimental conditions. Additionally, the laboratory in Heidelberg was carefully prepared to have very stable environmental conditions. Experimental challenges and the first Heidelberg results with the new spectrometer are presented.     

Analysis of coefficient identification problems associated to the inverse Euler-Bernoulli beam theory

A rigorous investigation of the identification of a heterogeneousflexural rigidity coefficient in the Euler-Bernoulli steady-statebeam theory in the presence of a prescribed load is presented.Mathematically, this study is an extension to higher-order differentialequations of the coefficient identification problem analysedby Marcellini (1982) for the one-dimensional Poisson equation.In addition, various types of boundary conditions are discussed.Conditions for the well-posedness of these inverse problemsare established and, furthermore, numerical results obtainedusing a regularization algorithm are presented.     

A critical investigation of the effects of the radio frequency potential on the trapping of externally injected ions in ion trap mass spectrometry

The sensitivity of all ion trap mass spectrometry (ITMS) methods is dependent on the trapping efficiency of the instrument. For ITMS instruments utilizing external ion sources, such as laser desorption, trapping efficiency is known to depend on the phase and amplitude of the radio frequency (RF) potential applied to the ring electrode at the time of ion introduction. It is remarkable that, in a considerable body of literature, no consensus exists regarding the effects of these parameters on the efficacy of trapping externally generated ions. In this paper, a summary of the literature is presented in order to highlight significant discrepancies. New laser desorption ion trap mass spectrometry (LD-ITMS) data are also presented, from which conclusions are drawn in our effort to clarify some of the confusion. Copyright 1999 John Wiley & Sons, Ltd.     

The UW-PTMS

The University of Washington Penning Trap Mass Spectrometer (UW-PTMS) is now producing measurements with uncertainties approaching 10 parts per trillion (ppt). We have recently published (Van Dyck, Jr. et al., Int J Mass Spectrom 251:231–242, 2006) detailed analysis of several systematic shifts which can be important at this level of accuracy. Experimental studies of these effects in our older PTMS, combined with preliminary analysis of ²H data, and re-analysis of the previously reported ⁴He (Van Dyck, Jr. et al., Phys Rev Lett 92:220802/1, 2004) and ¹⁶O (Van Dyck, Jr. et al., Hyperfine Interact 132:163–175, 2001) data, gives more accurate atomic mass values for ¹⁶O, ⁴He, and ²H. Currently we are taking data for a new measurement of the ³He atomic mass, and working on some improvements to the PTMS, including a new amplifier system for phase-sensitive detection of the ion’s axial motion, and a new computer-controlled ultra-stable voltage source for the Penning trap’s ring electrode, used to adjust the ion’s axial frequency. These new systems will allow us to simultaneously manipulate individual ions in two nearby Penning traps, and some sources of noise will be the same for both traps. We plan to investigate several techniques which should reduce measurement time and improve accuracy by working with the two ions simultaneously. This material is supported by the National Science Foundation under Grant No. 0353712.     

Ultraprecise atomic mass measurement of the alpha particle and 4He

The atomic masses of the alpha particle and 4He have been measured by means of a Penning trap mass spectrometer which utilizes a frequency-shift detector to observe single-ion cyclotron resonances in an extremely stable 6.0 T magnetic field. The present resolution of this instrument approaches 0.01 ppb [10 ppt (parts per trillion)] and is limited primarily by the effective stability (<5 ppt/h) of the magnet over hundreds of hours of observation. The leading systematic shift [at -202(9) ppt] is due to the image charge located in the trap electrodes. The new value for the atomic mass of the alpha particle is 4 001 506 179.147(64) nu and the corresponding value for the mass of 4He is 4 002 603 254.153(64) nu (nu=10(-9) u). The 16 ppt uncertainty is at least 20 times smaller than any previous determination.     

Ab initio studies of structural features not easily amenable to experiment: Part 15. The influence of solvation on molecular structure in some formic acid and carbonic acid hydrates

The completely relaxed ab initio geometries (4—21G) of a trihydrate of carbonic acid and of the monohydrates of cis and trans formic acid are compared with the corresponding unhydrated structures. The maximum structural changes caused by hydration in the free acid structures are of the order of magnitude of 0.03 Å and 3° for bond distances and bond angles, respectively. The corresponding changes in free and complexed water are 0.005 Å and 5°, respectively. The results are significant for the general problem of the transferability of gas phase molecular structures to molecules in solution and for estimates of the uncertainties in theoretical hydration energy surfaces which are generated by using fixed, monomer geometries for water and solvate molecules. Compared with the free geometries, the sum total of the structural changes in some of the systems studied corresponds to energies of several kcal mol^?1.