Behavior of crystalline silicon under huge electronic excitations: A transient thermal spike description

Recent experimental works devoted to the phenomena of mixing observed at metallic multilayers Ni/Si irradiated by swift heavy ions irradiations make it necessary to revisit the insensibility of crystalline Si under huge electronic excitations. Knowing that Ni is an insensitive material, such observed mixing would exist only if Si is a sensitive material. In order to extend the study of swift heavy ion effects to semiconductor materials, the experimental results obtained in bulk silicon have been analyzed within the framework of the inelastic thermal spike model. Provided the quenching of a boiling ( or vapor) phase is taken as the criterion of amorphization, the calculations with an electron-phonon coupling constant g(300 K) = 1.8 x 10(12) W/cm(3)/K and an electronic diffusivity D-e(300 K) = 80 cm(2)/s nicely reproduce the size of observed amorphous tracks as well as the electronic energy loss threshold value for their creation, assuming that they result from the quenching of the appearance of a boiling phase along the ion path. Using these parameters for Si in the case of a Ni/Si multilayer, the mixing observed experimentally can be well simulated by the inelastic thermal spike model extended to multilayers, assuming that this occurs in the molten phase created at the Ni interface by energy transfer from Si. (C) 2009 Elsevier B. V. All rights reserved.

Experimental study on heavy ion single event effects in SOI SRAMs

Silicon-on-insulator (SOI) technologies have been developed for radiation-hardened military and space applications. The use of SOI has been motivated by the full dielectric isolation of individual transistors, which prevents latch-up. The sensitive region for charge collection in SOI technologies is much smaller than for bulk-silicon devices potentially making SOI devices much harder to single event upset (SEU). In this study, 64 kB SOI SRAMs were exposed to different heavy ions, such as Cu, Br, I, Kr. Experimental results show that the heavy ion SEU threshold linear energy transfer (LET) in the 64 kB SOI SRAMs is about 71.8 MeV cm(2)/mg. Accorded to the experimental results, the single event upset rate (SEUR) in space orbits were calculated and they are at the order of 10(-13) upset/(day bit).

An outlook of heavy ion driven plasma research at IMP-Lanzhou

Since the successful completion of the cooling storage ring (CSR) project in China at the end of 2007, high qualitative heavy ion beams with energy ranging from keV to GeV/u have been available at the Heavy Ion Research Facility at Lanzhou (HIRFL). More than 10(9) 1 GeVlu C6+ particles or 10(8) 235 MeV/u Xe particles can be stored in the CSR main-ring and extracted within hundred nano-seconds during the test running, the beam parameters will be improved in the coming years so that high energy density (HED) conditions could be achieved and investigated there. Recent scientific results from the experiments relevant to plasma research on HIRFL are summarized. Dense plasma research with intense heavy ion beams of CSR is proposed here.

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 Sn-132+Sn-124 reactions at beam energies of 200, 400, 600 and 800MeV 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.

Systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses

A systematic study of the pi(-)/pi(+) ratio in heavy-ion collisions with the same neutron/proton ratio but different masses can help single out effects of the nuclear mean field on pion production. Based on simulations using the IBUU04 transport model, it is found that the pi(-)/pi(+) ratio in head-on collisions of Ca-48 + Ca-48, Sn-124 + Sn-124, and Au-197 + Au-197 at beam energies from 0.25 to 0.6 GeV/nucleon increases with increasing the system size or decreasing the beam energies. A comprehensive analysis of the dynamical isospin fractionation and the pi(-)/pi(+) ratio as well as their time evolution and spatial distributions demonstrates clearly that the pi(-)/pi(+) ratio is an effective probe of the high-density behavior of the nuclear symmetry energy.

Cell cycle and apoptosis alteration of human hepatocarcinoma cells by subclinical-dose C-12(6+)-beam irradiation

Objective The purpose of this study is to investigate the effect of subdinical-dose C-12(6+)-beam irradiation on cell cycle and cell apoptosis in hepatocarcinoma cells. Materials and methods The HepG(2) cells were exposed to 0-2.0 Gy of either the C-12(6+) beam or a gamma-ray. Cell survival was detected by clonogenic assay. Cell cycle was determined by flow-cytometry analysis. The apoptosis was monitored by fluorescence microscope with DAPI staining. p53 and p21 expression were detected by Western blot. Results The G(0)/G(1) cells in the irradiated groups were significantly more than those in the control (P<0.05). The C-12(6+)-ion irradiation had a greater effect on the cell cycle of HepG(2) cells (including promoting G(1)-phase and G(2)-phase arrest) than gamma-ray irradiation. The apoptotic cells induced by C-12(6+) beam were significantly more numerous than those induced by gamma-ray (P<0.05). The carbon ions had a stronger effect on p53 and p21 expression than the gamma-ray irradiation. The survival fractions for cells irradiated by C-12(6+) beam were significantly smaller than those irradiated by gamma-ray (P<0.05).

Average property of fragmentation reaction and momentum dissipation induced by halo-nuclei in heavy ion collisions

We study systematically the average property of fragmentation reaction and momentum dissipation induced by halo-nuclei in intermediate energy heavy ion collisions for different colliding systems and different beam energies within the isospin dependent quantum molecular dynamics model (IQMD). This study is based on the extended halo-nucleus density distributions, which indicates the average property of loosely inner halo nucleus structure, because the interaction potential and in-medium nucleon-nucleon cross section in IQMD model depend on the density distribution. In order to study the average properties of fragmentation reaction and momentum dissipation induced by halo-nuclei we also compare the results for the halo-nuclear colliding systems with those for corresponding stable colliding systems with same mass under the same incident channel condition. We find that the effect of extended halo density distribution on the fragment multiplicity and nuclear stopping (momentum dissipation) are important for the different beam energies and different colliding systems. For example the extended halo density distributions increase the fragment multiplicity but decrease the nuclear stopping for all of incident channel conditions in this paper.

Photoluminescence character of Xe ion irradiated sapphire

In the present work the photoluminescence (PL) character of sapphire implanted with 180 keV Xe and irradiated with 308 MeV Xe ions was studied. The virgin, implanted and irradiated samples were investigated by PL and Fourier transform infrared (FTIR) spectra measurements. The obtained PL spectra showed the maximum emission bands at 2.75, 3.0 and 3.26 eV for the implanted fluence of 1.0 x 10(15) ions/cm(2) and at 2.4 and 3.47 eV for the irradiated fluence of 1.0 x 10(13) ions/cm(2). The FTIR spectra showed a broaden absorption band between 460 and 630 cm(-1), indicating that strong damaged region formed in Al2O3.

Cross sections for transfer ionization in ion-helium collisions

A simple model has been developed within the independent-particle model (IPM) based on the Bohr-Lindhard model and classical statistical model. Cross sections for transfer ionization of helium by ions A(q+) (q = 1-3) are calculated for impact energies between 10 and 6000 keV/u. The calculated cross sections are in good agreement with the experimental data of helium by He(1-2)+ and Li(1-3)+.

Modification of ZnO films under high energy Xe-ion irradiations

ZnO films were deposited on (100) Si substrate by radio frequency magnetron sputtering. These films were irradiated at room temperature with 308 MeV Xe-ions to a fluence of 1.0 x 10(12), 1.0 x 10(13) or 1.0 x 10(14) Xe/cm(2). Then the samples were investigated using RBS, XRD, FESEM and PL analyses. The obtained experimental results showed that the deposited ZnO films were highly c-axis orientated and of high purity, 308 MeV Xe-ion irradiations could not change the c-axis oriented. The topography and PL properties of the ZnO films varied with increasing the Xe-ion irradiation fluence. For 1.0 x 10(13) or 1.0 x 10(14) Xe/cm(2) irradiated samples, surface cracks were observed. Furthermore, it was found that the 1.0 x 10(14) Xe/cm(2) irradiated sample exhibiting the strongest PL ability. The modification of structure and PL properties induced by 308 MeV Xe-ion irradiations were briefly discussed. (C) 2008 Elsevier B.V. All rights reserved.

Beam dynamics design of an RFQ for a planned accelerator, which uses a direct plasma injection scheme

To meet the requirements of providing high-intensity heavy ion beams the direct plasma injection scheme (DPIS) was proposed by a RIKEN-CNS-TIT collaboration. In this scheme a radio frequency quadrupole (RFQ) was joined directly with the laser ion source (LIS) without a low-energy beam transport (LEBT) line. To find the best design of the RFQ that will have short length, high transmission efficiency and small emittance growth, beam dynamics designs with equipartitioning design strategy and with matched-only design strategy have been performed, and a comparison of their results has also been done. Impacts of the input beam parameters on transmission efficiency are presented, too. (C) 2008 Elsevier B.V. All rights reserved.

Neutron-proton bremsstrahlung from intermediate energy heavy-ion reactions as a probe of the nuclear symmetry energy?

Hard photons from neutron-proton bremsstrahlung in intermediate energy heavy-ion reactions are examined as a potential probe of the nuclear symmetry energy within a transport model. Effects of the symmetry energy on the yields and spectra of hard photons are found to be generally smaller than those due to the currently existing uncertainties of both the in-medium nucleon-nucleon cross sections and the photon production probability in the elementary process pn -> pn gamma. Very interestingly, nevertheless, the ratio of hard photon spectra R-1/2(gamma) from two reactions using isotopes of the same element is not only approximately independent of these uncertainties but also quite sensitive to the symmetry energy. For the head-on reactions of Sn-132 + Sn-124 and Sn-112 + Sn-112 at E-beam/A = 50 MeV, for example, the R-1/2(gamma) displays a rise up to 15% when the symmetry energy is reduced by about 20% at rho = 1.3 rho(0) which is the maximum density reached in these reactions. (C) 2008 Elsevier B.V. All rights reserved.