Search for the Halo Effect in the ^1H（^6He,^6Li）n Reaction

The angular distributions of the charge exchange reaction ^1H(^6He,^6Li)n were measured in reverse kinematics with a secondary ^6He beam at the energy of 4.17 A MeV.The data were analysed in the context of a microscopic calculation.It is shown that both the ground state of ^6He and the second excited state of ^6Li(3.563MeV,0^ ) have a halo structure.     

Quasi—elastic Scattering of a Secondary ^6He Beam on a ^9Be Target at 25MeV／Nucleon

The quasi-elastic scattering of a secondary ^6He beam (25MeV/n) on a ^9Be target has been measured for the first time with the application of a sophisticated tracking detector system.The angular distribution is reported.A phenomenological optical potential is obtained by fitting the experimental data,which encourages more accurate experimental measurements.     

A Sensitivity Test of Extracting the Optical Potential Parameters for 6He＋209Bi from the Transfer Reaction 208pb（7Li,6He）209Bi

Recently, an indirect method has been proposed to study the optical model potential of exotic nuclear systems by fitting the transfer reaction angular distribution. The sensitivity test of this transfer method is performed with 2~8 pb（T Li,6 He）2~9 Bi as an example, by varying the potential parameters individually. The results indicate that, except for the ambiguity in the real potential depth V, other optical potential parameters of 6He＋209Bi as well as the structural information of the reactions can be extracted reliably, Moreover, the radius parameter of the bound state, rbound, is an extraordinarily sensitive parameter, which should be taken care of in the calculation procedure. The present work provides a theoretical reference for the application of the transfer method.     

Simulation and analysis of 13N+p elastic resonance scattering

The ^13 N＋p elastic resonance scattering has been studied at the secondary radioactive beam facility of CIAE in inverse kinematics via a thick-target method. The excitation function for the ^13N（p,p） scattering was obtained in the energy interval of Ecru ≈0.5-3.2 MeV with a ^13 N secondary beam of （47.8±1.5） MeV. Careful analysis of the secondary beam components and extensive Monte-Carlo simulations enable the resolution of the experimental proton spectra. The resonance parameters for five low-lying levels in ^14 O were deduced by Rmatrix fitting calculations with MULTI7 and SAMMY-M6-BETA. The present results show general agreement with those from a recent similar work, and thus confirm the observation of a new 0^- level at 5.7 MeV in 140 with an improved width of 400（45） keV.     

Monte Carlo simulation of electron beam air plasma characteristics

A high-energy electron beam generator is used to generate a plasma in atmosphere. Based on a Monte Carlo toolkit named GEANT4, a model including complete physics processes is established to simulate the passage of the electron beam in air. Based on the model, the characteristics of the electron beam air plasma are calculated. The energy distribution of beam electrons (BEs) indicates that high-energy electrons almost reside in the centre region of the beam, but low-energy electrons always live in the fringe area. The energy deposition is calculated in two cases, i.e., with and without secondary electrons (SEs). Analysis indicates that the energy deposition of SEs accounts for a large part of the total energy deposition. The results of the energy spectrum show that the electrons in the inlet layer of the low-pressure chamber (LPC) are monoenergetic, but the energy spectrum of the electrons in the outlet layer is not pure. The SEs are largely generated at the outlet of the LPC. Moreover, both the energy distribution of BEs and the magnitude of the density of SEs are closely related to the pressure of LPC. Thus, a conclusion is drawn that a low magnitude of LPC pressure is helpful for reducing the energy loss in the LPC and also useful for greatly increasing the secondary electron density in dense air.     

Off-axis dose distribution for rectangle proton beam

This papcr modifies an analytical algorithm originally developed for electron dose calculations to evaluate the off-axis dose distribution of rectangle proton bcam. This spatial distribution could be described by Fermi-Eyges theory since a proton undergoes small-angle scattering when it passes through medium. Predictions of the algorithm for relative off-axis dose distribution by a 6 cm ＊ 6 cm initial monoenergetic proton beam are compared with the results from the published Monte Carlo simulations. The excellent level of agreement between the results of these two methods of dose calculation （〈 2%） demonstrates that the off-axis dose distribution from rectangle proton beam may be computed with high accuracy using this algorithm. The results also prompts the necessity to consider the off-axis distribution when the proton is applied to clinical radiotherapy since the penumbra is significant at the distal of its range （about 0.6 cm at the Bragg-peak depth）.     

Supercontinuum Gneneration and Modes Analysis in Secondary Cores of a Hollow-Core Photonic Crystal Fiber

We demonstrate the generation of supercontinuum spectra in three secondary cores of a hollow-core photonic crystal fiber pumped by femtosecond laser pulses, respectively. The supercontinuum spectra are mainly a result of the soliton self-frequency shift and an amplification of dispersive wave at visible wavelengths. Detailed mode simulations show that with the increasing core length, the modes transfer from ＂double-points＂ to ＂single-point＂ since the pump laser is more easily coupled into the two side cores of a secondary core when the core length is small. The simulation results also explain why the experimental observed far-field beam patterns of first two secondary cores are different.     

Measurement of ^2H（^8Li, ^9Be）n Reaction Relevant to Primordial Nucleosynthesis

The angular distribution of the ^2H（^8Li, ^9Be）n （ground state） reaction, important to primordial nucleosynthesis in the inhomogeneous model, has been measured at E = 8.1 MeV using a secondary ^8Li beam. Cross section of this reaction was determined to be 9.0 4±3.4 mb. According to the cross section, the astrophysical S-factor was calculated to be 272 4±103 keV b. It is shown that ^2H（8^Li, ^9Be）n （ground state） reaction is important for creating 9Be, but less important for destroying aLl in primordial nucleosynthesis.     

Optical nonlinearity measurement of 4-（N-methyl,N-hydroxyethl）amino,4＇-nitroazobenzene using a transmittance technique with a phase object（T-PO） with top-hat beams at 600-nm wavelength

The transmittance technique with a phase object（T-PO）,for measuring optical nonlinear coefficients is proposed with a top-hat beam.The sensitivity of the T-PO with a top-hat beam is a factor of 4 greater than that with a Gaussian beam.The validity of this method is verified by measuring the nonlinearity of a well-characterized liquid,CS 2 at 532-nm wavelength.The ease of use of this method has been proved by measuring a new compound 4-（N-methyl,N-hydroxyethyl）amino,4＇-nitroazobenzene（ANAB） at 600-nm wavelength,indicating that this method can be extended to the measurement of optical nonlinearities in a wide-band spectrum.     

Experimental study on helium optical electron polarimetry

Optical electron polarimetry is suitable for calibration of a spin-polarized electron source, especially for measurement of polarization of spin-polarized electron beam. In this paper, a new optical electron polarimeter is described, which is based on the circularly polarized He radiation induced by the bombarding of He atoms with spin-polarized electrons. The theoretical basis of the optical electron polarimetry and the structure of the optical electron polarimeter are discussed. The measurement of polarization of spin-polarized electrons produced from a new GaAs （100） spin-polarized electron source is carried out. The result of polarization of 30.8% for our spin-polarized electron source is obtained using the He optical electron polarimeter.     

Measurement of the Breakup Cross Sections in ^6He＋^9Be Reaction at 25 MeV／Nucleon

The breakup reaction cross sections were measured for the reaction of^6He at 25 MeV/nucleon from ^9Be target with intensity of 10^5 pps. By fitting the energy spectra of breakup α particles with Gaussian functions, the angular distribution of differential cross sections in the laboratory system has been extracted and compared with the Serber model calculations. The good agreement between the calculation and the experimental data favours a dominant configuration of the ^4He core plus valence neutrons for the structure of^6He.     

Collisional quantum interference on rotational energy transfer： physical interpretation of the differential interference angle

Collisional quantum interference （CQI） on the intramolecular rotational energy transfer is observed in an experiment with a static cell, and the integral interference angles are measured. To obtain more accurate information, an experiment with a molecular beam is carried out, and thereby the relationship between the differential interference angle and the scattering angle is obtained. Based on the first-Born approximation of time-dependent perturbation theory, the theoretical model of CQI is developed in an atom-diatom system in the condition of the molecular beam, with the long-range interaction potential taken into account. The method of measuring correctly the differential interference angle is presented. The tendencies of the differential interference angle changing with the impact parameter and rel- ative velocity are discussed. The theoretical model presented here is important for understanding or performing the experiment in the molecular beam.     

Axial distribution of Gaussian beam limited by a hard-edged aperture

In this letter, the axial distribution of Gaussian beam limited by a hard-edged aperture is studied. We theoretically analyze the axial diffraction of Gaussian beam limited by a hard-edged aperture, and give the simpler formulas of the axial diffraction intensities of Gaussian beam in Fresnel diffraction field and Fraun-hofer diffraction field. The corresponding numerical calculation of axial diffraction intensity distribution of Gaussian beam with different wave waist is provided and the evolution of the diffraction distribution with the wave waist of Gaussian beam is explained. As the especial cases of the truncated Gaussian beam, the Gaussian beam in free space and the parallel light limited by the aperture are discussed too, and the system parameters of the truncated Gaussian beam which can cause it to equal to these cases are given. The theoretical results conform to the numerical analysis.     

Two Electron Transfer and Stabilization in Slow O^6＋ and Rare-Gas Collisions

The stabilization ratios R for double-electron transfer, i.e., the cross section ratios of true double capture to total double-electron transfer, are measured in O^6＋ ＋He, Ne and Ar collisions at 6 keV/u. A high R value about 68% is obtained for the He target, while for the Ar target, the R value is only 8%. The high R value for the He target is due to the significant direct population of the （2l, nl′ ） configurations with high n. For the Ar target, the （quasi）symmetric configurations （3l, nl′） lead to the much lower R value. Neglecting the core effects, the O^6＋ ion can be taken as a bare ion C^6＋ except the occupied ls shell, and then the measured R values are compared with previous experimental results of C^6＋ projectile ions at Ne and Ar target, while the occupied ls shell for the C^6＋ ＋He collisions. similar impact velocity. It yields good agreement with the O^6＋ ＋He system results in a higher R value than that in     

Irradiation effect of yttria-stabilized zirconia by high dose dual ion beam irradiation

Yttria-stabilized zirconia （YSZ） is irradiated with 2.0-MeV Au2＋ ions and 30-keV He＋ ions. Three types of He, Au, Au ＋ He （successively） ion irradiation are performed. The maximum damage level of a sequential dual ion beam implanted sample is smaller than single Au ion implanted sample. A comparable volume swelling is found in a sequential dual ion beam irradiated sample and it is also found in a single Au ion implanted sample. Both effects can be explained by the partial reorganization of the dislocation network into weakly damaged regions in the dual ion beam implanted YSZ. A vacancy-assisted helium trapping/diffusion mechanism in the dual ion beam irradiated condition is discussed. No phase transformation or amorphization behavior happens in all types of ion irradiated YSZ.     

Optical Trapping of Double-Ring Radially Polarized Beam with Improved Axial Trapping Efficiency

Radially polarized beams, focused by a high numerical aperture （NA） objective, have non-propagating fields along the propagation axis in the focal region, which leads to a higher axial trapping efficiency in comparison with linearly polarized beams. We propose a design for converting a lowest-order radially polarized beam （R-TEM01） to a double-ring radial polarization distribution （DR R-TEM01） through a specially designed polarization rotator. The phases of the two rings of this beam differ by π. Numerical results evaluated by rigorous T-matrix method show that the DR R-TEM01 beam can improve the axial trapping efficiency compared with the R-TEM01 beam, provided that the size of trapped particles is of order of the wavelength of the beam.     

Modal Characterization of a Planar Waveguide in Bismuth Borate Crystal

We report on the fabrication and modal property studies of planar waveguide structure in x-cut bismuth borate biaxial crystal formed by He ion implantation with triple energies. The prism coupling method is used to measure the effective refractive indices of this waveguide. We reconstruct the refractive index distribution of this waveguide by the reflectivity calculation method. Our results indicate that a broadened optical barrier is produced by the multiple He ion implantations. The so-called tunneling effect of the non-stationary mode in this type of barrier waveguide is presented by the well-known finite difference beam propagation method.     

Single-row laser beam with energy strengthened ends for continuous scanning laser surface hardening of large metal components

For laser surface hardening of metal components with large superficies,a binary grating is proposed to generate single-row laser beam with proportional-intensity diffractive orders.To obtain a uniform hardened band distribution and improve the wear resistance of the sample surface,the binary grating is designed to produce single-row laser beam with energy strengthened at the two ends.The profile of the laser beam spot was designed to be strip with high length-width ratio to improve the machining efficiency of the hardening of large surfaces.A new advantage is suggested to obtain proportional intensity spots with evenness.The design results show that the diffractive efficiency of the binary grating is more than 70%,and the uniformity is less than 3%.The surface profile of the grating fabricated was measured,which shows that the fabrication error is less than 2%.The application of the binary grating in the laser surface hardening of metal components with large superficies is experimentally investigated,and the results show that the hardness distribution of the modified layer is more uniform than that hardened by Gaussian laser beam or array spots with equal intensity distribution.     

Cross Section of Heavy Ion Reaction （14.5 MeV/u） ^132Xe ＋ Bi

We investigate the cross section of the heavy ion reaction （14.5 MeV/u） ^132Xe ＋ Bi by using a CR-39 plastic track detector. The target-detector assembly is exposed at UNILAC beam facility of GSI, Germany. After etching under appropriate etching conditions, the detector is scanned for multipronged events produced as a result of interactions of projectile ions with target atoms. The elastic events are separated from binary events and used for the determination of the quarter-point angle. The quarter-point angle obtained is used to determine the total reaction cross section. The total experimental reaction cross section is determined by using statistics of inelastic events of two-pronged and higher multiplicity events. The experimental reaction cross sections determined by using elastic and inelastic data observed in the reaction under study are found to be in good agreement with the theoretically calculated value of reaction cross section using a sharp cutoff model.     

Continuously transferring cold atoms in caesium double magneto-optical trap

We have established a caesium double magneto-optical trap (MOT) system for cavity-QED experiment, and demonstrated the continuous transfer of cold caesium atoms from the vapour-cell MOT with a pressure of ～ 1×10^-6 Pa to the ultra-high-vacuum (UHV) MOT with a pressure of ～ 8×10^-8 Pa via a focused continuous-wave transfer laser beam. The effect of frequency detuning as well as the intensity of the transfer beam is systematically investigated, which makes the transverse cooling adequate before the atoms leak out of the vapour-cell MOT to reduce divergence of the cold atomic beam. The typical cold atomic flux got from vapour-cell MOT is ～2×10⁷ atoms/s. About 5×10⁶ caesium atoms are recaptured in the UHV MOT.