Rectification in substituted atomic wires: a theoretical insight

Recently, there have been discussions that the giant diode property found experimentally in diblock molecular junctions could be enhanced by the many-body electron correlation effect beyond the mean field theory. In addition, the effect of electron-phonon scattering on an electric current through the diode molecule, measured by inelastic tunneling spectroscopy (IETS), was found to be symmetric with respect to the voltage sign change even though the current is asymmetric. The reason for this behavior is a matter of speculation. In order to clarify whether or not this feature is limited to organic molecules in the off-resonant tunneling region, we discuss the current asymmetry effect on IETS in the resonant region. We introduced heterogeneous atoms into an atomic wire and found that IETS becomes asymmetric in this substituted atomic wire case. Our conclusion gives the other example of intrinsic differences between organic molecules and metallic wires. While the contribution of electron-phonon scattering to IETS is not affected by the current asymmetry in the former case, it is affected in the latter case. The importance of the contribution of the electron-hole excitation to phonon damping in bringing about the current asymmetry effect in IETS in the latter case is discussed.     

Poly(styrene)-based graded-index plastic optical fiber for home networks

We investigated poly(styrene) (PSt)-based graded-index plastic optical fiber (GI-POF) with low loss and high bandwidth for home networks. To install the GI-POF in home networks, the attenuation must be below 200 dB/km at a 670-680 nm wavelength, and the bandwidth must be over 2.0 GHz for the 50 m fiber. In this study, we selected a dibenzothiophene (DBT) as a dopant to PSt, and we fabricated PSt-DBT-based GI-POF. We confirmed that the PSt-DBT-based GI-POF has high bandwidth (4.4 GHz) for 50 m fiber and low loss (166-193 dB/km) at a 670-680 nm wavelength and obtained the GI-POF that satisfied the requirements for home networks.     

Dose rate estimates due to gas bremsstrahlung for a photon shutter and collimator unit of the VESPERS beamline at the Canadian Light Source

A radiation shielding study against primary and secondary gas bremsstrahlung is carried out for a tungsten collimator/stop, which is one of the components employed in the VESPERS beamline at the Canadian Light Source. The dose and dose rate are obtained by calculating the energy deposition in a water phantom which surrounds the collimator/stop unit. The dose rate behind a vacuum hole of the collimator/stop which leads to the experimental hutch is closely examined. The dose rates are further investigated with the addition of a tungsten shutter that is positioned in front of the collimator/stop.     

Decay of the new isotope127Pr

A new isotope,¹²⁷Pr, has been identified and its decay has been studied using on-line isotope separation of⁹⁴Mo (³⁶Ar,p2n) reaction products. The half-life of the isotope was determined to be 7.7(6) s, and a /X-ray spectrum has been obtained. A partial level scheme is proposed for¹²⁷Ce on the basis of-singles,-gated and-coincidence data.The authors would like to thank the TIARA cyclotron crew for their cooperation in generating an intense³⁶Ar beam as well as in operating the cyclotron. This work was partly supported by the JAERI-University Collaborative Research Project.     

In-beam γ -ray study of the neutron-rich nuclei 240U, 246Pu, and 250Cm produced by the (18O, 16O) reaction

We have measured deexcitation γ rays in the neutron-rich nuclei of ²⁴⁰U, ²⁴⁶Pu, and ²⁵⁰Cm produced by the (¹⁸O, ¹⁶O) two-neutron transfer reactions, in coincidence with the ¹⁶O particles using Si ΔE−E detectors. The γ rays in these nuclei were identified by selecting the kinetic energies of ¹⁶O particles, which correspond to the excitation energies in the residual nuclei below the neutron separation energies. The ground-state bands of ²⁴⁰U, ²⁴⁶Pu, and ²⁵⁰Cm were established up to 12⁺ states and the K ^π = 0⁻ octupole band of ²⁴⁰U was established up to 9⁻ states. The systematics of the moments of inertia of the ground-state bands for actinide nuclei shows that the deformed subshell closure at N = 152 is sustained for ₉₆Cm isotopes and that it disappears for ₉₄Pu isotopes. The text was submitted by the authors in English.     

Fast scintillation processes in CsCl crystals comprising semiconductor nanocrystals

We analyzed the scintillation mechanism in CsCl single crystals comprising CsPbCl₃-like semiconductor nanocrystals. A decay component with a subnanosecond lifetime was observed and ascribed to the exciton luminescence in the nanocrystals. This is the first observation of scintillation from semiconductor nanocrystals. In addition, slower components were observed and ascribed to the intraionic transition at isolated Pb²⁺ ions and the Auger-free luminescence in the CsCl matrix. Furthermore, it was shown that the nanocrystals absorbed and re-emitted the scintillation photons from the isolated Pb²⁺ ions. The results in this report clearly indicates that the semiconductor nanocrystals function as ultrafast “luminescent centers,” and complicated scintillation dynamics are observed due to the luminescence from different components in the crystal and the radiative energy transfer between them.     

Photo-stimulated luminescence of KCl:Eu under X-ray and ion irradiation

We compared the photo-stimulated luminescence (PSL) process of storage phosphor KCl:Eu under the irradiation of X-ray, 2.0 MeV H⁺ ions and 2.0 MeV He⁺ ions. The purpose of the irradiation of H⁺ and He⁺ ions was to mimic the irradiation effects of neutrons. In each case, it was revealed that F-centers were involved in the PSL process. We observed an entirely different fluence-dependent PSL behavior between the X-ray and the ion irradiation, whereas the behavior of the F-center absorption was quite similar. This difference was due to the different yields of the trapping sites for the electrons liberated from the F-centers, and the difference in the yield was ascribed to the difference in the excitation density. This result clearly indicated a marked difference in the PSL process under X-ray and neutron irradiations and indicated that the analysis of the PSL process under ion irradiation is highly important for the application of PSL phosphors to neutron radiography.     

Measurement of high-pT single electrons from heavy-flavor decays in p + p collisions at square root of s = 200 GeV

The momentum distribution of electrons from decays of heavy flavor (charm and bottom) for midrapidity absolute value of y < 0.35 in p + p collisions at square root of s = 200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.3 < pT < 9 GeV/c. Two independent methods have been used to determine the heavy-flavor yields, and the results are in good agreement with each other. A fixed-order-plus-next-to-leading-log perturbative QCD calculation agrees with the data within the theoretical and experimental uncertainties, with the data/theory ratio of 1.71+/-0.02stat+/-0.18sys for 0.3 < pT < 9 GeV/c. The total charm production cross section at this energy has also been deduced to be sigma cc = 567+/-57stat+/-193sys microb.