Optimizing a microwave gas ion source for continuous-flow accelerator mass spectrometry

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of American Institute of Physics for personal use, not for redistribution. The definitive version was published in Review of Scientific Instruments 83 (2012): 02B304, doi:10.1063/1.3656408.A 2.45 GHz microwave ion source coupled with a magnesium charge exchange canal (CxC) has been successfully adapted to a large acceptance radiocarbon accelerator mass spectrometry system at the National Ocean Sciences AMS Facility (NOSAMS), Woods Hole Oceanographic Institution. CO2 samples from various preparation sources are injected into the source through a glass capillary at 370 µl/min. Routine system parameters are about 120 - 140 µA of negative 12C current after the CxC, leading to about 400 14C counts per second for a modern sample and implying a system efficiency of 0.2%. While these parameters already allow us to perform high quality AMS analyses on large samples, we are working on ways to improve the output of the ion source regarding emittance and efficiency. Modeling calculations suggest modifications in the extraction triode geometry, shape and size of the plasma chamber could improve emittance and hence ion transport efficiency. Results of experimental tests of these modifications are presented.This work has been supported by the US National Science Foundation through Cooperative Agreement OCE-0753487

Mean-field calculations of quasi-elastic responses in 4He

We present calculations of the quasi-elastic responses functions in 4He based upon a mean-field model used to perform analogous calculations in heavier nuclei. The meson exchange current contribution is small if compared with the results of calculations where short-range correlations are explicitly considered. It is argued that the presence of these correlations in the description of the nuclear wave functions is crucial to make meson exchange current effects appreciable.Comment: uuencoded file containing 7 LaTex peges plus 3 ps figures. To be published in Physical Review

Superscaling of Inclusive Electron Scattering from Nuclei

We investigate the degree to which the concept of superscaling, initially developed within the framework of the relativistic Fermi gas model, applies to inclusive electron scattering from nuclei. We find that data obtained from the low energy loss side of the quasielastic peak exhibit the superscaling property, i.e., the scaling functions f(\psi') are not only independent of momentum transfer (the usual type of scaling: scaling of the first kind), but coincide for A \geq 4 when plotted versus a dimensionless scaling variable \psi' (scaling of the second kind). We use this behavior to study as yet poorly understood properties of the inclusive response at large electron energy loss.Comment: 33 pages, 12 color EPS figures, LaTeX2e using BoxedEPSF macros; email to [email protected]

High-precision Studies of the 3^{\bf{3}}He(e,e′^{\bf{\prime}}p) Reaction at the Quasielastic Peak

Precision studies of the reaction $^{3}$He(e,e$^\prime$p) using the three-spectrometer facility at the Mainz microtron MAMI are presented. All data are for quasielastic kinematics at $|\vec{q} | =685$ MeV/c. Absolute cross sections were measured at three electron kinematics. For the measured missing momenta range from 10 to 165 MeV/c, no strength is observed for missing energies higher than 20 MeV. Distorted momentum distributions were extracted for the two-body breakup and the continuum. The longitudinal and transverse behavior was studied by measuring the cross section for three photon polarizations. The longitudinal and transverse nature of the cross sections is well described by a currently accepted and widely used prescription of the off-shell electron-nucleon cross-section. The results are compared to modern three-body calculations and to previous data.Comment: 4 pages, 3 figures. Submitted for publication in Phys. Rev. Let

Quasielastic 12C(e,e'p) Reaction at High Momentum Transfer

We measured the 12C(e,e'p) cross section as a function of missing energy in parallel kinematics for (q,w) = (970 MeV/c, 330 MeV) and (990 MeV/c, 475 MeV). At w=475 MeV, at the maximum of the quasielastic peak, there is a large continuum (E_m > 50 MeV) cross section extending out to the deepest missing energy measured, amounting to almost 50% of the measured cross section. The ratio of data to DWIA calculation is 0.4 for both the p- and s-shells. At w=330 MeV, well below the maximum of the quasielastic peak, the continuum cross section is much smaller and the ratio of data to DWIA calculation is 0.85 for the p-shell and 1.0 for the s-shell. We infer that one or more mechanisms that increase with $\omega$ transform some of the single-nucleon-knockout into multinucleon knockout, decreasing the valence knockout cross section and increasing the continuum cross section.Comment: 14 pages, 7 figures, Revtex (multicol, prc and aps styles), to appear in Phys Rev

Direct application of compound-specific radiocarbon analysis of leaf waxes to establish lacustrine sediment chronology

Author Posting. © Springer, 2007. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Journal of Paleolimnology 39 (2008): 43-60, doi:10.1007/s10933-007-9094-1.This study demonstrates use of compound-specific radiocarbon analysis (CSRA) for dating Holocene lacustrine sediments from carbonate-hosted Ordy Pond, Oahu, Hawaii. Long-chain odd-numbered normal alkanes (n-alkanes), biomarkers characteristic of terrestrial higher plants, were ubiquitous in Ordy Pond sediments. The δ13C of individual n-alkanes ranged from −29.9 to −25.5‰, within the expected range for n-alkanes synthesized by land plants using the C3 or C4 carbon fixation pathway. The 14C ages of n-alkanes determined by CSRA showed remarkably good agreement with 14C dates of rare plant macrofossils obtained from nearby sedimentary horizons. In general, CSRA of n-alkanes successfully refined the age-control of the sediments. The sum of n-alkanes in each sample produced 70–170 μg of carbon (C), however, greater age errors were confirmed for samples containing less than 80 μg of C. The 14C age of n-alkanes from one particular sedimentary horizon was 4,155 years older than the value expected from the refined age-control, resulting in an apparent and arguable age discrepancy. Several lines of evidence suggest that this particular sample was contaminated by introduction of 14C-free C during preparative capillary gas chromatography. This study simultaneously highlighted the promising potential of CSRA for paleo-applications and the risks of contamination associated with micro-scale 14C measurement of individual organic compounds.This project was funded by Petroleum Research Fund (PRF #40088-ACS) and in part by Sigma Xi, The Scientific Research Society (Grants in aid of research, 2003)

On the nature of banks

Two views exist regarding the nature of the banking business. The dominant view defines banks as financial intermediaries – institutions in the business of transferring money from savers to borrowers. An alternative view advances that banks finance borrowers via money creation. I explain the differences between these two views and argue for the superiority of the latter one as a description of modern banking. I discuss the implications for economic analysis and explain how the connection between bank lending and money creation helps us understand the effects of banking on economic activity

Kostenanalyse telemedizinischer Schlaganfallbehandlung. Veränderung der stationären Behandlungskosten und Pflegekosten am Beispiel des Telemedizinischen Projekts zur integrierten Schlaganfallversorgung in Bayern (TEMPiS).

Hintergrund: Die Behandlung auf TeleStroke-Units führt im Vergleich zur unspezialisierten Schlaganfalltherapie zu einem verbesserten Patienten-Outcome. Diese Arbeit untersucht, wie sich dieses neue Behandlungskonzept auf die Kosten der stationären und der nachstationären Versorgung auswirkt. Methoden: Analysiert wurden die stationären Behandlungskosten und die Pflegeversicherungs-Leistungen von Schlaganfallpatienten (versichert bei der AOK Bayern), die im telemedizinisch unterstützten Schlaganfall-Netzwerk TEMPiS (Telemedizinisches Projekt zur integrierten Schlaganfallversorgung) behandelt wurden, im Vergleich zu Schlaganfallpatienten aus gematchten Kliniken ohne spezialisiertes Therapieangebot und ohne Telemedizinanbindung. Die Kosten der Kranken- und Pflegeversicherung wurden über 30 Monate nachbeobachtet. Zum Ausschluss von vorbestehenden Unterschieden zwischen den Kliniken wurde zusätzlich ein Zeitraum vor der Netzwerk-Einführung untersucht. Ergebnisse: Im Zeitraum nach der Netzwerkeinführung wurden 1 277 Schlaganfallpatienten (767 TEMPiS-Kliniken; 510 Vergleichskliniken) untersucht. Die Patienten der Interventions-Kliniken hatten über 30 Monate einen signifikant günstigeren Verlauf hinsichtlich der Pflegestufen-Einteilung. Diese Behandlung war zwar mit höheren akutstationären Kosten (5 309 € vs. 4 901 €, p=0,04), jedoch mit geringeren Pflegeversicherungs-Leistungen (3 946 € vs. 5 132 €; p=0,04) verbunden. Die erfassten absoluten Gesamtkosten im Beobachtungszeitraum waren in beiden Gruppen gleich - die Pflegeversicherungs-Leistungen pro überlebtem Patientenjahr in der Interventionsgruppe niedriger (1 953 € vs. 2 635 €; p=0,005). Im Zeitraum vor TEMPiS-Einführung ergaben sich keine signifikanten Outcome- und Kostendifferenzen zwischen den Klinikgruppen. Schlussfolgerungen: Die erhöhten Kosten für die akute telemedizinische Schlaganfall-Behandlung im Netzwerk wurden durch niedrigere Folgekosten kompensiert