Browsing by Author "Nakamura, T"
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- ItemCompatibility of atmospheric 14CO2 measurements: comparing the heidelberg low-level counting facility to international accelerator mass spectrometry (AMS) laboratories(Cambridge University Press, 2016-09-19) Hammer, S; Friedrich, R; Kromer, B; Cherkinsky, A; Lehman, SJ; Meijer, HAJ; Nakamura, T; Palonen, V; Reimer, RW; Smith, AM; Southen, JR; Szidat, S; Turnbull, J; Uchida, MCombining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal. © 2016 by the Arizona Board of Regents on behalf of the University of Arizona
- ItemA first step toward small-mass AMS radiocarbon analysis at Nagoya University(GNS Science, 2010-03-22) Minami, M; Miyata, Y; Nakamura, T; Hua, QWe have started to establish a small-mass sample preparation system at Nagoya University. In the first step, NIST Ox-II standard samples <0.5 mgC, graphitized using our regular sample preparation protocol, were measured for 14C. The 14C/12C ratios of these small-mass samples were affected by the decrease in beam current intensity and incomplete graphitization especially for samples <0.3 mgC. In the second step, we have designed a compact graphitization system suitable for small-mass samples and compared its performance to that of our regular graphitization system. During the graphitization reaction following our regular protocol, by-product water vapor was incompletely trapped, which resulted in low graphite yield or no graphitization for samples of <0.5 mgC. Meanwhile graphite was successfully produced for samples of 0.2mgC using the new reactor. The SEM images of small-samples using the new reactor show spotted graphite covering the spherical iron particles. No or very little graphite was observed for the samples graphitized using our regular graphitization system. During the graphitization reaction using the sealed tube method, water vapor was incompletely trapped, which resulted in low graphite yield especially for samples of <0.5 mgC. Meanwhile graphite was successfully produced for samples of 0.2mgC using the new reactor. The cold trap at −80°C employed in the new graphitization system was effective in trapping water for small-mass samples. The combination of lower temperature for trapping water and a reduction in reactor volume delivered higher graphitization efficiency for small samples. We are now ready for 14C analysis of samples of around 0.2mgC. We also report an example of stepwise combustion of samples containing sulfur in a closed tube to produce graphite successfully. Copyright (c) 2010 AMS12
- ItemMagnetic and electronic co states in the layered cobaltate GdBaCo2O5.5-x(American Physical Society, 2008-08) García-Fernández, M; Scagnoli, V; Staub, U; Mulders, AM; Janousch, M; Bodenthin, Y; Meister, D; Patterson, BD; Mirone, A; Tanaka, Y; Nakamura, T; Grenier, S; Huang, YJ; Conder, KWe have performed nonresonant x-ray diffraction, resonant soft and hard x-ray magnetic diffraction, soft x-ray absorption, and x-ray magnetic circular dichroism measurements to clarify the electronic and magnetic high-spin (HS) state at the states of the Co3+, ions in GdBaCo2O5.5. Our data are consistent with a Co-Py(3+) pyramidal sites and a Co-Oc(3+), low-spin (LS) state at the octahedral sites. The structural distortion with a doubling of the a axis (2a(p)X2a(p)X2a(p) cell) shows alternating elongations and contractions of the pyramids, and indicates that the metal-insulator transition is associated with orbital order in the t(2g) orbitals of the Co-Py(3+) HS state. This distortion corresponds to an alternating ordering of xz and yz orbitals along the a and c axes for the Co-Py(3+). The orbital ordering and pyramidal distortion lead to deformation of the octahedra but the Co-Oc(3+) LS state does not allow an orbital order to occur for the Co-Oc(3+), ions. The soft x-ray magnetic diffraction results indicate that the magnetic moments are aligned in the ab plane but are not parallel to the crystallographic a or b axes. The orbital order and the doubling of the magnetic unit cell along the c axis support a noncollinear magnetic structure. The x-ray magnetic circular dichroism data indicate that there is a large orbital magnetic contribution to the total ordered Co moment. © 2008, American Physical Society
- ItemResonant x-ray diffraction and the observation of strange quantities(Australian Institute of Physics, 2012-02-02) Princep, AJ; Mulders, AM; Schierle, E; Weschke, E; Hester, JR; Hutchinson, WD; Tanaka, Y; Terada, N; Narumi, Y; Staub, U; Scagnoli, V; Nakamura, T; Kikkawa, A; Lovesey, SW; Balcar, ECondensed matter physics has a growing reputation for providing an opportunity to observe exotic particles and states of matter that have an analogue in other areas of physics. Examples of this include the observation of Dirac strings and magnetic monopoles in spin-ice materials [1], spinon / holon separation in gated nanowires [2], and toroidal moments (anapoles) in the ubiquitous cuprates [3]. Resonant X-ray Diffraction (RXD) is well suited to the observation of a variety of quantities that behave differently under time reversal, coordinate inversion, and rotation [4]. It is possible to distinguish between competing orders and we have determined the orbital order in RB2C2, including higer order terms (as illustrated on the cover page) [5,6]
- ItemSmall-mass AMS radiocarbon analysis at Nagoya University(Elsevier Science BV, 2013-01-01) Minami, M; Kato, T; Miyata, Y; Nakamura, T; Hua, QAs part of the ongoing development at the AMS facility of the Center for Chronological Research at Nagoya University to radiocarbon (C-14) analyze samples smaller than 0.5 mg carbon (mgC), a compact graphitization manifold has been built. Tests with various reference materials show it performs well for samples as small as 0.1 mgC. Preparation with this new system is compared with the performance of the older protocol for regular-sized samples. Furthermore, it is shown that the addition of Cu and Ag before and stepwise heating during sealed-tube combustion of samples with high S content improve the degree of conversion to CO2 without having to resort to special purification measures such as the use of Co3O4 + Ag reagent and an n-pentane/LN2 trap before graphitization. © 2013, Elsevier Ltd.
- ItemTriakontadipole and high-order dysprosium multipoles in the antiferromagnetic phase of DyB2C2(IOP Publishing Ltd., 2011-07-06) Princep, AJ; Mulders, AM; Staub, U; Scagnoli, V; Nakamura, T; Kikkawa, A; Lovesey, SW; Balcar, EResonant soft x-ray Bragg diffraction at the Dy M-4,M-5 edges has been used to study Dy multipoles in the combined magnetic and orbitally ordered phase of DyB2C2. The analysis incorporates both the intra-atomic magnetic and quadrupolar interactions between the 3d core and 4f valence shells. Additionally, we introduce to the formalism the interference of magnetic and nonmagnetic oscillators. This allows a determination of the higher-order multipole moments of rank 1 (dipole) to 6 (hexacontatetrapole). The strength of the Dy 4f multipole moments have been estimated as being up to 80% of the quadrupolar moment.(c) 2011 IOP Publishing LTD