Ih Structure Research Articles

メタンハイドレートの相変化とその地球惑星科学的意義

Methane hydrate, called as “fiery ice”, is expected to be a fruitful natural resource, at the same time, methane is rather effective greenhouse gas than carbon dioxide. And, methane hydrate is thought to be the dominant constituent of the outer planets and their moons. Recent high-pressure studies on gas hydrate, including methane hydrate, have accumulated to give us a great deal of understanding of the structural changes in gas hydrates. A feature of structural changes in terms of pressure and guest size is summarised in the former part of this paper. The gas hydrate with the guest size from argon to methane finally take a common filled ice Ih structure, although they have different initial and intermediate structures. In the latter part, retention of the filled ice Ih structure of methane hydrate up to 42 GPa is described. In-situ x-ray diffractometry and optical observation revealed the existence of the filled ice structure with the volume change of 40% and large anisotropic compressibility. The meanings of the structural changes and the retention to very high pressure of methane hydrate on geological science and planetary science are also described.

U 4+ Mevva source & outlook for HIF sources

A high particle current in a short time period (100 μs) is required to fill the synchrotron at GSI to its space charge limit. The new high current injector consisting of a RFQ and an IH structure accepts ions with a mass-to-charge ratio m/ q up to 65 with a space charge limit of 0.25 emA×m/q . As a source for metallic ions we will use the Metal Vapor Vacuum Arc ion source. A main concern of this source is the reliability and the stability of the extracted ion beam. In addition the splitting of the total voltage (extraction voltage and acceleration voltage) required to achieve the injection energy of 2.2 keV/u has a strong influence on the beam quality. First measurements along the beam line in front of the new accelerator will be presented.

Structure and dynamics of N2–IH

The ground state rotational spectra and internal dynamics in five isotopomers N214–IH, N214–ID, N215–IH, N14N15–IH, and N15N14–IH of the nitrogen–hydrogen iodine dimer have been investigated by pulsed-nozzle, Fourier-transform microwave spectroscopy. Analysis of the recorded spectra yields rotational, centrifugal distortion, nuclear quadrupole and spin-rotation coupling constants for the five isotopomers. The spectroscopic constants are interpreted in terms of a ground-state NN–IH structure using the parameters rcm, kσ, and the oscillation angles θN2 and θHI of the N2 and IH moieties. For N214–IH, the values rcm=4.197 872(67) Å, kσ=1.461 52(32) N/m, θN2=25.61(22)°, and θHI=23.454 6(91)° are obtained. The rotational transitions of N214–IH, N214–ID, and N215–IH show a doubling, which is a consequence of tunneling associated with the interchange of the two nitrogen nuclei. The experimental findings are compared with results from ab initio calculations.

The IH structure—a new approach to the fusion RF linac

Short zero degree synchronous particle structures and magnetic focusing lenses can be combined in such a way that the emittance of each section is well adapted to the acceptance of the following section. By that way drift tube linacs can do the particle acceleration more close to the crest of the RF wave, the transverse RF defocusing effect can be minimized and the emittance growth of the beam is kept low. Specific problems of the heavy-ion fusion linacs are the acceleration of 1+charged ions with mass numbers around 200 and beam currents around 100 mA. This paper investigates the suitability of theInterdigitalH-type structure for that application. Technical as well as beam-dynamical aspects and the beam-cavity interaction are discussed.

Measurement of17O quadrupole interactions and identification of the diamagnetic fraction in ice by muon level crossing resonance

By means of Level Crossing Resonance in a sample of ice which is enriched in H217O, the final diamagnetic state of implanted positive muons is determined to be the muonium-substituted molecule HMuO, accommodated in the regular and fully relaxed Ih structure. The17O quadrupole coupling constant is measured to be 6.1 MHz at 200 K assuming an asymmetry parameter close to unity, a decrease of about 5% relative to that in normal ice Ih at 77 K. The isotope effect is attributed to a greater polarization in the vicinity of a muonium (as opposed to a normal hydrogen) bond. At 50 K, an additional resonance is observed which could correspond to a precursor state, so far not definitely identified. One possibility is a muon trapped at a Bjerrum L-defect, giving a {H2O−Mu−OH2}+ species with an,17O quadrupole coupling constant of 8.2 MHz and asymmetry parameter of 0.55. Above this temperature, the fall in the (Gaussian) line-width parameter is attributed to the increasing rate of proton or muon migration, the correlation time dropping from 4 μs at 80 K to 1 μs near the melting-point. The increase in the diamagnetic fraction with rise in temperature is attributed to the increasing proportion of trapping sites available for muon capture.

Construction and operating experience with the Tokyo Institute of Technology post accelerators

A multipurpose heavy-ion accelerator system has been constructed to generate beams for material science, atomic physics and nuclear solid-state physics. The system consists of a 1.6-MV tandem, a high energy gain ( E out E in = 10 ) and a low energy gain ( E out E in = 1.4 ) Wideröe linear accelerator with an IH structure. The accelerating characteristics have been studied, and operation experiences during the last 18 months are reported.

The upgraded Munich linear heavy ion postaccelerator

The linear postaccelerator at the Munich tandem laboratory was extended by a second resonator cavity and a de-/rebuncher, which both have twice the frequency of the first tank. The simple construction principle and the high shunt impedance of the first cavity, an IH structure, can be transferred onto the sections of a long linac by using a special kind of beam dynamics. In addition to the postacceleration of heavy ions, this method also provides an economical acceleration of low energy beams with small q/ A values. The second Munich postaccelerator section has an effective shunt impedance of 167 MΩ/ m for β = 0.1 , its total length is 3 m. The de-/rebuncher (5–7 gaps) shows that also short IH structures are very effective.

Experimental studies on the optimization of the accelerating field distribution in an IH lineac

A new method is being studied to control the accelerating field distribution in an IH lineac with a high energy gain. In spite of its high shunt impedance, a shortcoming of an IH structure is that a concentration of accelerating field occurs at the low-energy section of the cavity. One of the practical methods to control the accelerating-gap voltages is adjusting the electric-capacity distribution of the structure. This method, however, is not always suitable for an IH lineac when the particle-energy gain is larger than the incident particle energy. The basic idea of our experiments is to utilize an inductive method to “tune” the accelerating field distribution. In order to test the applicability of this method, accelerating field distributions and shunt impedances are measured in terms of these “tuner” configurations by using 1 4 scale models. The results are compared with the calculations based on a four-terminal network simulation.

Molecular model for ice clusters in a supersaturated vapor

A molecular model previously applied to prenucleation water clusters is used to examine ice Ih embryos. The canonical partition function is evaluated for clusters having from 6 to 64 water molecules. The intermolecular vibrational free energies are extrapolated to clusters containing up to 120 molecules and free energies of formation, nucleation rates, and critical supersaturation ratios are calculated and compared with experiment. For the clusters studied, the ice Ih structure appears to be much less stable at all temperatures than the more spherical clathratelike cluster.

Proton Distribution in Ice and the Kirkwood Correlation Factor

4096 molecules of water forming an ice Ic structure and 2048 molecules forming an ice Ih structure, with standard periodic boundary conditions in each case, have been used to calculate the dipole correlations which arise from proton allocation to the oxygen nuclei according to the Bernal-Fowler ice rules. The calculations reveal a substantial antiparallel correlation in the coordination shells at about twice the distance of the nearest neighbors in the lattice. The value of gK, the Kirkwood correlation factor, is found to be 2.07±0.02 for ice Ih. For ice Ic the value, determined with less precision, is 2.11±0.10. In connection with Kirkwood's dielectric formula the value of gK implies an effective dipole moment, μs, of the molecule in the solid ice Ih phase equal to 2.92 D.