Hu Bi-Tao

Generation of isolated attosecond pulses in bowtie-shaped nanostructure with three-color spatially inhomogeneous fields*

We theoretically investigate high-order harmonic generation in a two-color multi-cycle inhomogeneous field combined with a 27th harmonic pulse. By considering a bowtie-shaped gold nanostructure, the spatiotemporal profiles of enhanced plasmonic fields are obtained by solving the Maxwell equation using finite-domain time-difference method. Based on quantum-mechanical and classical models, the effect of 27th harmonic pulse, temporal profile of enhanced plasmonic field and inhomogeneity on supercontinuum generation are analyzed and discussed. As a result, broadband supercontinuum can be generated from our approach with optimized gap size of nanostructure. Moreover, these results are not sensitively dependent on the relative phase in the two-color field.

Half-Lives for Alpha Radioactivity of Elements with 104 ? Z ? 120 within Unified Fission Model

α decay half-lives are calculated using the Qα values obtained by Semi-empirical Shell Model in the framework of the Unified Fission Model (UFM) with the Coulomb repulsion, nuclear attraction due to proximity potential, and rotational energy due to angular momentum transfer of α particle. In addition, the calculated and experimental half-lives of 425 nuclei are compared to check the validity of the model applied on α decay. The calculated half-lives of α decay are in good agreement with the experimental data. Finally, some useful predications on the α decay half-lives are provided for future experiments.

Theoretical Analysis and New Formulae for Half-Lives of Proton Emission

The proton radioactivity half-lives of spherical proton emitters are calculated by the cluster model with the contribution of a centrifugal potential barrier considered separately. The results are compared with the experimental data and other theoretical data, and good agreement is found for most nuclei. In addition, two formulae are proposed for the proton decay half-life of spherical proton emitters through the least squares fit to the experimental data available, and could reproduce the experimental half-lives successfully.

Helium-Implantation-Induced Damage in NHS Steel Investigated by Slow-Positron Annihilation Spectroscopy

Evolutions of defects and helium contained defects produced by atomic displacement and helium deposition with helium implantation at different temperatures in novel high silicon (NHS) steel are investigated by a slow positron beam. Differences of the defect information among samples implanted by helium to a fluence of 1 x 10(17) ions/cm(2) at room temperature, 300 degrees C, 450 degrees C and 750 degrees C are discussed. It is found that the mobility of vacancies and vacancy clusters, a recombination of vacancy-type defects and the formation of the He-V complex lead to the occurrence of these differences. At high temperature irradiations, a change of the diffusion mechanism of He atoms/He bubbles might be one of the reasons for the change of the S-parameter.

Cavity Swelling in Three Ferritic-Martensitic Steels Irradiated by 196 MeV Kr Ions

We report on cavity swelling at peak damage regions of three ferritic-martensitic (FM) steels (NHS, RAFM and T91) irradiated by 196 MeV Kr ions at different temperatures (450/550°C). Cavity configurations of the irradiated specimens are investigated by transmission electron microscopy with cross-section technique. For home-made reduced activation ferritic-martensitic (RAFM) and T91 steels irradiated at 450°C, both large size and bimodal size distribution of the cavity are found in their peak damage regions, whereas novel high silicon (NHS) steel exhibits good swelling resistance at different irradiation temperatures. Temperature relativity of the cavity swelling in NHS, RAFM and T91 steels is discussed briefly.

The energy loss of 12C and 11B ions in seven elements

Abstract The present work provides previously unpublished stopping powers for 11B and 12C ions in Co, Ni, In, Pd, Gd, Lu and Ta targets in the energy region ∼1–5 MeV. The experimental results were compared with TRIM91 and SRIM96 predictions. The experimental stopping powers for 12C in Co, Ni, In, Pd, and Ta agree with theoretical predictions within several percents, but do not agree well in Gd and Lu. In the velocity-proportional region, a linear dependence of stopping power on the velocity of projectile ion was observed. 4He energy loss was taken as the measure of the sample foil thickness and the obtained thicknesses were confirmed by low energy (

Collective Transverse Flow in Intermediate Energy Heavy-Ion Collisions

Within the hadronic transport model IBUU04, we study the density-dependent symmetry energy by using the neutron-proton differential flow from the 132Sn+124 Sn reactions at beam energies of 200, 400, 600 and 800 MeV per nucleon. The strong effect of the symmetry energy is shown at the incident beam energy of 400 MeV/A. The small medium-effect of the neutron-proton differential flow is also found. We also study the neutron-proton differential flows with impact parameters of 3, 5, 7 fm. It is found that in semi-central collisions the sensitivity of the neutron-proton differential flow to the symmetry energy is larger.

Study on spatial resolution of micromegas as a neutron detector under condition of high neutron flux and γ ray background

In this paper Micromegas has been designed to detect neutrons. The simulation of the spatial resolution of Micromegas as neutron detector is carried out by GEANT4 toolkit. The neutron track reconstruction method based on the time coincidence technology is employed in the present work. The influence of the flux of incident 14 MeV neutron and high gamma background on the spatial resolution is carefully studied. Our results show that the spatial resolution of the detector is sensitive to the neutron flux, but insensitive to the intensity of γ background if the neutron track reconstruction method proposed by our group is used. The γ insensitivity makes it possible for us to use the Micromegas detector under condition which has high γ-rays background.

Stopping powers of Pd, Lu and Gd for 1.0–5.0 MeV 7Li ions

Stopping powers of 7Li ions in Pd, Lu and Gd were measured near their maximum with experimental error less than 6%. The experimental results were compared with TRIM91 and SRIM96 predictions. The 4He energy loss was taken as the measure of the sample foil thickness. The effective charge ratios of 7Li ions to hydrogen were examined and found to be a complex function of ion energy.

Characterization of Femtosecond Laser-Induced Plasma under Low Pressure in Argon*

An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium (LTE), the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.