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Abstract: Simple bio-molecules demonstrate a propensity to form hydrogen-bonded networks. Here, individual hydrogen-bond energies are determined through topological analysis of the theoretical electron density for a variety of systems, demonstrating the existence of a universal relationship between hydrogen-bond length and strength. Comparison of local hydrogen-bond strength to global stabilisation allows the quantification of contributions to intermolecular interactions within surface overlayers in unprecedented detail. [Copyright &y& Elsevier]

We have measured the acoustoelectric current generated in a GaAs/Al0.33Ga0.67As heterostructure incorporating an In0.1Ga0.9As layer at the heterointerface. This wafer is designed to give a two-dimensional electron gas with a high electron g factor. We demonstrate that this wafer is of sufficient quality to produce quantized acoustoelectric current plateaus and has potential for future spintronic and quantum information technology applications. [ABSTRACT FROM AUTHOR]

Long-lived isomers in 212Bi have been studied following 238U projectile fragmentation at 670 MeV per nucleon. The fragmentation products were injected as highly charged ions into a storage ring, giving access to masses and half-lives. While the excitation energy of the first isomer of 212Bi was confirmed, the second isomer was observed at 1478(30) keV, in contrast to the previously accepted value of >1910 keV. It was also found to have an extended Lorentz-corrected in-ring half-life >30 min, compared to 7.0(3) min for the neutral atom. Both the energy and half-life differences can be understood as being due a substantial, though previously unrecognized, internal decay branch for neutral atoms. Earlier shell-model calculations are now found to give good agreement with the isomer excitation energy. Furthermore, these and new calculations predict the existence of states at slightly higher energy that could facilitate isomer deexcitation studies. [ABSTRACT FROM AUTHOR]

Excited states in 180Hg were populated using the 147Sm(36Ar,3n)180Hg reaction and studied by in-beam conversion-electron spectroscopy. Conversion electrons emitted at the target position were measured using the Silicon Array for Conversion Electron Detection (SACRED) spectrometer and tagged through the characteristic decays of 180Hg detected in a position-sensitive silicon strip detector located at the focal plane of the gas-filled recoil separator Recoil Ion Transport Unit (RITU). Electron conversion of transitions previously assigned to 180Hg through in-beam v-ray spectroscopy studies was identified up to the 10+ → 8+ transition and the intensities of the conversion-electron transitions were found to be consistent with the previous multipolarity assignments. Evidence was also found for two highly converted transitions in 180Hg: a 167 keV transition is interpreted as the transition from the newly identified Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed, while a 420 keV transition is assigned as the E0 decay from the 0+ bandhead of the prolate-deformed configuration to the weakly deformed ground state. [ABSTRACT FROM AUTHOR]

The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in 256Rf, which suggest that a long-lived, low-energy 8- isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a 256Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-μs isomer was identified. However, its low population, ∼5(2)% that of the ground state instead of the expected ∼30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z = 104, which describes nuclei with Z = 92-103 very well. [ABSTRACT FROM AUTHOR]

The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry Aγ with respect to the neutron spin direction of γ rays emitted in the reaction n→+p→d+γ using the capture of polarized cold neutrons on the protons in a liquid parahydrogen target. One expects parity-odd effects in the hadronic weak interaction between nucleons to be induced by the weak interaction between quarks. Aγ in n→+p→d+γ is dominated by a ΔI=1, 3S1-3P1 parity-odd transition amplitude in the n-p system. The first phase of the measurement was completed at the Los Alamos Neutron Science Center spallation source (LANSCE), with the result Aγ=[-1.2±2.1 (stat.)±0.2 (sys.)]×10-7. We also report the first measurement of an upper limit for the parity-allowed left-right asymmetry in this reaction, with the result Aγ,LR,=[-1.8±1.9 (stat.)±0.2 (sys.)]×10-7. In this paper we give a detailed report on the theoretical background, experimental setup, measurements, extraction of parity-odd and parity-allowed asymmetries, analysis of potential systematic effects, and LANSCE results. The asymmetry has an estimated size of 5×10-8 and the aim of the NPDGamma collaboration is to measure it to 1×10-8. The second phase of the measurement will be performed at the Spallation Neutron Source at Oak Ridge National Laboratory. [ABSTRACT FROM AUTHOR]

Using standard microfabrication techniques, it is now possible to construct devices that appear to reliably manipulate electrons one at a time. These devices have potential use as building blocks in quantum computing devices, or as a standard of electrical current derived only from a frequency and the fundamental charge. To date, the error rate in semiconductor 'tuneable-barrier' pump devices, those which show most promise for high-frequency operation, have not been tested in detail. We present high-accuracy measurements of the current from an etched GaAs quantum dot pump, operated at zero source-drain bias voltage with a single ac-modulated gate at 340MHz driving the pump cycle. By comparison with a reference current derived from primary standards, we show that the electron transfer accuracy is better than 15 parts per million. Highresolution studies of the dependence of the pump current on the quantum dot tuning parameters also reveal possible deviations from a model used to describe the pumping cycle. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate charge pumping in semiconducting carbon nanotubes by a traveling potential wave. From the observation of pumping in the nanotube insulating state we deduce that transport occurs by packets of charge being carried along by the wave. By tuning the potential of a side gate, transport of either electron or hole packets can be realized. Prospects for realization of nanotube-based single electron pumps are discussed. [Copyright &y& Elsevier]

Evidence for the decay of non-yrast states in 254No has been observed for the first time in an experiment performed at the University of Jyväskylä. The experiment employed the JUROGAM array of germanium detectors coupled to the gas-filled recoil separator RITU and the focal-plane spectrometer GREAT. The ground-state rotational band has been tentatively extended up to a spin of 24ℏ and has a smoothly behaving dynamical moment of inertia. It is speculated that the observation of high-energy γ-rays is due to the decay of a K = 3 band-head state. [ABSTRACT FROM AUTHOR]

Dense samples (10–100 bar cm) of nuclear spin polarized 3He are utilized in high energy physics, neutron scattering, atomic physics, and magnetic resonance imaging. Metastability exchange optical pumping can rapidly produce high 3He polarizations (≈80%) at low pressures (few mbar). We describe a polarized 3He gas compressor system which accepts 0.26 bar l h-1 of 3He gas polarized to 70% by a 4 W neodymium doped lanthanum magnesium hexaluminate (Nd:LMA) laser and compresses it into a 5 bar cm target with final polarization of 55%. The spin relaxation rates of the system’s components have been measured using nuclear magnetic resonance and a model of the 3He polarization loss based on the measured relaxation rates and the gas flow is in agreement with a 3He polarization measurement using neutron transmission. [ABSTRACT FROM AUTHOR]

A neutron polarizer-analyzer system based on polarized 3 He is being developed at KEK Pulsed Neutron Source for an experiment on time reversal invariance in the nuclear reaction at J-PARC. [ABSTRACT FROM AUTHOR]

A radiation hard, compact, ion chamber detector system is described. The chambers are planar, with narrow gaps, and are filled with nitrogen gas. They operated at a signal rate equivalent to ∼2×108 minimum ionizing tracks per cm2, delivered in pulses 250 ns long, while monitoring an intense scattered electron flux. [Copyright &y& Elsevier]

The (π+,pd), and (π+,dd) reactions on 6Li and 12C targets were investigated with pions of 100 and 165 MeV kinetic energy. The experimental apparatus employed for this work is characterized by good energy resolution (<3%, ΔE/E) and angle definition (Δθ=1.6°), and the measurements span a large fraction of the final-state particle phase space. Results are compared to extensive Monte Carlo simulations in order to investigate the role of single-step and multistep absorption processes in these nuclei. In comparison with previously published (π+,pp) data on the same targets and at the same beam energies, specific kinematic regions were identified in which the neutron hard pickup process n+p→d dominated the observed deuteron yield. The contribution of direct quasitriton absorption is significant only at 100 MeV. [Copyright &y& Elsevier]

We demonstrate single-electron pumping in a gate-defined carbon nanotube double quantum dot. By periodic modulation of the potentials of the two quantum dots, we move the system around charge triple points and transport exactly one electron or hole per cycle. We investigate the pumping as a function of the modulation frequency and amplitude and observe good current quantization up to frequencies of 18 MHz where rectification effects cause the mechanism to break down. [ABSTRACT FROM AUTHOR]

The authors demonstrate the feasibility of ballistic electron spectroscopy as a tool for mesoscopic physics. A quantum dot is utilized as an energy-selective detector of nonequilibrium ballistic electrons injected into a two-dimensional electron system. In this letter they use a second quantum dot as the electron injector to evaluate the scheme. They propose an application in the study of interacting one- and zero-dimensional systems. [ABSTRACT FROM AUTHOR]

A sapphire cell was used to obtain a high 3He nuclear polarization by means of spin-exchange optical pumping. The phase-shift difference between ordinary and extraordinary rays is well controlled using the thickness of the birefringent sapphire window so that a high circular polarization is obtained in the cell. Neutron transmission through the polarized 3He gas was measured as a function of neutron energy. A large 3He polarization of 63±1% was obtained at a 3He pressure of 3.1 atm. Neutron polarizations of 97 and 90 % were obtained with transmission rates of 15 and 22 % at 10 and 20 meV, respectively. [ABSTRACT FROM AUTHOR]

We present a thermometry scheme to extract the temperature of a two-dimensional electron gas by monitoring the charge occupation of a weakly tunnel-coupled 'thermometer' quantum dot using a quantum point contact detector. Electronic temperatures between 120 and 951 mK are measured with an accuracy of better than 1 mK in the best case, and agree with the lattice temperature measured by a resistance thermometer. The thermometer is non-invasive and does not pass a current through the electron system being measured. The tuning is independent of temperature, and the device is robust in a magnetic field up to 5.6 T. [ABSTRACT FROM AUTHOR]