Multi-Electron Processes in ^13C^6＋ Ions with Neon Collisions in Energy Region 4.15-11.08 keV/u

The cross-section ratios of double-, triple-, quadruple-, and the total multi-electron processes to the single electron capture process （σ^DE/σ^SC, σ^TE/σ^SC, σ^QE/σ^SC and σ^ME/σ^SC） as well as the relative ratios among reaction channels in double-electron active, triple-electron active and quadruple-electron active are measured in ^13C^6＋_Ne collision in the energy region of 4.15-11.08keV/u by employing position-sensitive and time-of-flight coincident techniques. It is determined that the cross-section ratios σ^DE /σ^SC, σ^TE /σ^SC, σ^QE /σ^SC and σ^ME /σ^SC are approximately the constants of 0.20 ± 0.03, 0.16 ± 0.04, 0.06 ± 0.02 and 0.42 ± 0.05. These values are obviously smaller than the predictions of the molecular Coulomb over-the-barrier model （MCBM） [J. Phys. B 23 （1990） 4293], the extended classical over-the-barrier model （ECBM） [J. Phys. B 19 （1986） 2925] and the semiempirical scaling laws （SL） [Phys. Rev. A 54 （1996） 4127]. However, the relative ratios among partial processes of DE, TE and QE are found to depend on collision energy, which suggests that the collision dynamics depends on the collision velocity. The limitation of velocity-independent character of ECBM, MCBM and SL is undoubtedly shown.     

Multiple Electron Capture Processes in Slow Collisions of Ar^9＋ Ions with Na Atoms

Slow collisions of highly charged ions with neutral atoms and molecules are of great importance in basic atomic collision physics, Recently, we built a new research facility for atomic physics at the Institute of Modern Physics. We report here the multiple electron transfer processes in collisions of Ar^9 with Na gas target at energy of 180 keV.     

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     

J/ψ Production in Ultra-Peripheral pp Collisions through aTwo-Photon Process

Using the photon spectrum of a high energy charged patton, we investigate the J/ψ production via the two photon interaction mechanism in ultra-peripheral pp collisions. It is shown that the contributions from the direct electromagnetic and the corresponding fragmentation processes are meaningful for the J/ψ productions in ultra-peripheral pp collisions at LHC energy.     

Single electron loss in and atomic the collisions of C^3＋ hydrogen

This paper studies the projectile electron loss cross sections of C^3＋ colliding with atomic hydrogen in the frame work of extended over-barrier model at intermediate velocities （25 keV/u-600 keV/u）. The electron loss is calculated in terms of the interaction between the screened target nucleus and the active projectile electron and of the interaction between projectile electron and target electron. Compared with the convergent close-coupling calculations, screening and anti-screening calculations, this model satisfactorily reproduces the experimentally obtained energy dependence of the electron-impact ionisation cross sections and the single electron loss cross sections over the energy range investigated here.     

Isospin Effect on Relative State Population Temperature in Reactions ^40Ar＋^112,124Sn at 30 MeV／u^1

An array of 13 detector telescopes has been used for detecting small-angle particle-particle correlations in the reactions ^40Ar^ 112,124Sn at 30 MeV/u. The α-α correlation functions were extracted from two-particle coincident events. A three-body trajectory code MENEKA was used to calculate the background correlation function. The detection efficiency was calculated by using the Monte-Carlo method.     

Double Electron Processes in Collisions of Partially Stripped Ions C^q＋ （q = 1-4） with Helium

The multi-electron processes are investigated for 17.9-120 keV/u C^1＋, 30-323 keV/u C^2＋, 120-438 keV/u ^C3＋, 287-480 keV/u C^4＋ incident on a helium target. The cross-section ratios of double electron （DE） process to the total of the single electron （SE） and the double electron process （i.e. SE＋DE）, the direct double electron （DDI） to the direct single ionization （DSI） as well as the contributions of DDI to DE and of TI to DE are measured using coincidence techniques. The energy and charge state dependences of the measured cross-section ratios are studied and discussed.     

Secondary Beam Fragments Produced by 200 and 400 MeV/u ^12C^6＋ Ions in Water

Based on the GEANT4 toolkit, we study the transportation of nucleons and nuclei in tissue-like media. The fragmentation of projectile nuclei and secondary interactions of produced nuclear fragments are considered. Livermore data is used to calculate electromagnetic interaction of primary and secondary charged particles. We validate the models using experimental data of 200 MeV/u and 400 MeV/u carbon ions, interacting with tissue equivalent materials of water. The model can well describe the depth-dose distributions in water and the doses measured for secondary fragments of certain charge and certain mass number. The secondary beam fragments produced by 200 MeV/u and 400 MeV/u ^12C^6＋ ions in water are investigated using the model. When the primary nuclei are in water, several neutron production mechanisms are involved. The light charged particles （p, d, t, ^3He and ^4He） and fast neutrons contribute to the dose tail behind the Bragg peak. The ^11C fragments which may be the most suitable nuclei for monitoring the energy deposition in carbon-ion therapy are also discussed.     

Experimental study of cross-section ratios in the collisions of Cq＋ and oq＋（q= 1-4） on atomic helium in strong-interaction region

We have measured the cross-section ratios of helium induced by C^q+ and O^q+ (q=1-4) in an energy range from 20 keV/amu to 500 keV/amu, and obtained the two-dimensional spectra by employing the coincidence method combined with the MPA-3 data acquisition system. Hence, we obtain the ratios of total single-ionization cross-sections (SI, SC, SLSI, and DLSI), total double-ionization cross-sections (DI, DC, TI, SLDI, and DLDI) and cross-sections of every process (SI, SC, SLSI, DLSI, DI, DC, TI, SLDI, and DLDI), which induce the single-ionization and double-ionization, to the total cross sections respectively. The competitive relations between the reaction-channels and the experimental data law of each reaction-channel are revealed explicitly, and the qualitative explanations involved in those results are also presented accordingly.