Damage to plasmid DNA induced by low energy carbon ions

The damage induced in supercoiled plasmid DNA molecules by 1-6 keV carbon ions has been investigated as a function of ion exposure, energy and charge state. The production of short linear fragments through multiple double strand breaks has been demonstrated and exponential exposure responses for each of the topoisomers have been found. The cross section for the loss of supercoiling was calculated to be (2.2 +/- 0.5) x 10(-14) cm(2) for 2 keVC(+) ions. For singly charged carbon ions, increased damage was observed with increasing ion energy. In the case of 2 keV doubly charged ions, the damage was greater than for singly charged ions of the same energy. These observations demonstrate that ion induced damage is a function of both the kinetic and potential energies of the ion.

Random walk of magnetic field lines for different values of the energy range spectral index

An analytical nonlinear description of field-line wandering in partially statistically magnetic systems was proposed recently. In this article the influence of the wave spectrum in the energy range onto field-line random walk is investigated by applying this formulation. It is demonstrated that in all considered cases we clearly obtain a superdiffusive behavior of the field-lines. If the energy range spectral index exceeds unity a free-streaming behavior of the field-lines can be found for all relevant length-scales of turbulence. Since the superdiffusive results obtained for the slab model are exact, it seems that superdiffusion is the normal behavior of field-line wandering.

Energy analysis of hyperthermal hydrogen atoms generated through surface neutralisation of ions

Hydrogen ions (H+, H-2(+) and H-3(+)) are produced in a magnetically confined inductively coupled radio frequency plasma. Ions are accelerated in the plasma boundary sheath potential, of several hundred volts, in front of a biased metal electrode immersed in the plasma. Backscattered hyperthermal hydrogen atoms are investigated by optical emission spectroscopy and an energy-resolved mass spectrometer. Ionisation of fast neutrals through electron stripping of atoms in the plasma allows energy analysis of the resulting ions. Thereby, the energy distribution function of the hyperthermal atoms can be deduced. The energy spectra can be explained as a superposition of individual spectra of the various ion species. The measured spectra also shows contributions of negative ions created at the electrode surface. In addition to experimental measurements, simulations of the neutral flux of backscattered atoms are carried out.

Two-electron QED contributions to the ground-state binding energy in He-like Kr34+ ions

The two-electron QED contributions to the ground-state binding energy of Kr34+ ions have been determined in two independent experiments performed with electron beam ion traps (EBIT) in Heidelberg (HD) and Tokyo (BT, Belfast-Tokyo collaboration). X rays arising from radiative recombination (RR) of free electrons to the ground state of initially bare Kr36+ and hydrogenlike Kr35+ ions were observed as a function of the interacting electron energy. The K edge absorption by thin Eu and W foils provided fixed photon energy references used to measure the difference in binding energy Delta E-2e between the H- and He-like Kr ions (Kr35+ and Kr34+, respectively). The two values agree well, yielding a final result of Delta E-2e=641.8 +/- 1.7 eV, confirming recent results of rigorous QED calculations. This accuracy is just of the order required to access screened radiative QED contributions.

Energy levels, radiative rates, and excitation rates for transitions in OIV

Aims. In this paper we report calculations for energy levels, radiative rates, and excitation rates for transitions in O IV. Methods. The grasp (general-purpose relativistic atomic structure package) and FAC (flexible atomic code) were adopted for calculating energy levels and radiative rates, and the Dirac atomic R-matrix code (DARC) used to determine the excitation rates. Results. Oscillator strengths and radiative rates are reported for all E1, E2, M1, and M2 transitions among the lowest 75 levels of O IV. Additionally, lifetimes are reported for all levels and comparisons made with those available in the literature. Finally, effective collision strengths are reported for all transitions over a wide temperature range below 106 K. Comparisons are made with earlier results and the accuracy of the data is assessed.

Energy levels, radiative rates and excitation rates for transitions in Ni XI

Aims. In this paper we report calculations for energy levels, radiative rates and excitation rates for transitions in Ni xi.
Methods. The grasp (General-purpose Relativistic Atomic Structure Package) and fac (Flexible Atomic Code) have been adopted
for calculating energy levels and radiative rates, and the Dirac Atomic R-matrix Code (darc) has been used to determine the excitation
rates.
Results. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest
250 levels of Ni xi. Additionally, lifetimes are also reported for all levels. However, results for excitation rates are presented only for
transitions among the lowest 17 levels.

Analysis procedure for calculation of electron energy distribution functions from incoherent Thomson scattering spectra

Incoherent Thomson scattering (ITS) provides a nonintrusive diagnostic for the determination of one-dimensional (1D) electron velocity distribution in plasmas. When the ITS spectrum is Gaussian its interpretation as a three-dimensional (3D) Maxwellian velocity distribution is straightforward. For more complex ITS line shapes derivation of the corresponding 3D velocity distribution and electron energy probability distribution function is more difficult. This article reviews current techniques and proposes an approach to making the transformation between a 1D velocity distribution and the corresponding 3D energy distribution. Previous approaches have either transformed the ITS spectra directly from a 1D distribution to a 3D or fitted two Gaussians assuming a Maxwellian or bi-Maxwellian distribution. Here, the measured ITS spectrum transformed into a 1D velocity distribution and the probability of finding a particle with speed within 0 and given value v is calculated. The differentiation of this probability function is shown to be the normalized electron velocity distribution function. (C) 2003 American Institute of Physics.

Energy levels and radiative rates for transitions in Co XI

Aims.In this paper we report calculations for energy levels and radiative rates for transitions in Co XI.

The Dissociative Recombination of Protonated Acrylonitrile, CH2CHCNH+, with Implications for Nitrile Chemistry in Dark Molecular Clouds and the Upper Atmosphere of Titan

Measurements on the dissociative recombination (DR) of protonated acrylonitrile, CH2CHCNH+, have been performed at the heavy ion storage ring CRYRING located in the Manne Siegbahn Laboratory in Stockholm, Sweden. It has been found that at~2meV relative kinetic energy about 50% of the DR events involve only ruptures of X–H bonds (where X=C or N)while the rest leads to the production of a pair of fragments each containing two heavy atoms (alongside H and/or H2). The absolute DR cross section has been investigated for relative kinetic energies ranging from ~1 meV to 1 eV. The thermal rate coefficient has been determined to follow the expression k(T) = 1.78 × 10-6 (T/300)-0.80 cm3 s-1 for electron temperatures ranging from ~10 to 1000 K. Gas-phase models of the nitrile chemistry in the dark molecular cloud TMC-1 have been run and results are compared with observations. Also, implications of the present results for the nitrile chemistry of Titan’s upper atmosphere are discussed.

Application to argon ions of a new technique to measure the two-electron contribution to the ground state energy of helium-like ions

We have measured the two-electron contribution of the ground state energy of helium-like argon ions using an electron beam ion trap (EBIT). A two-dimensional map was measured showing the intensity of x-rays from the trap passing through a krypton-filled absorption cell. The independent axes of this map were electron beam energy and x-ray energy. From this map, we deduced the two-electron contribution of the ground state of helium-like argon. This experimentally determined Value (312.4 +/- 9.5 eV) was found to be in good agreement with our calculated values (about 303.35 eV) and previous calculations of the same quantity. Based on these measurements, we have shown that a ten-day absorption spectroscopy run with a super-EBIT should be sufficient to provide a new benchmark value for the two-electron contribution to the ground state of helium-like krypton. Such a measurement would then constitute a test of quantum electrodynamics to second order.

Turbulent diffusion and mixing in interstellar dark clouds with adsorption onto grains

This paper reports the results of models of dark cloud chemistry incorporating a depth dependent density distribution with diffusive mixing and adsorption onto grains. The model is based on the approach taken by Xie et al. (1995), with the addition of grain accretion effects. Without diffusion, the central regions of the cloud freeze out in less than 10(7) years. Freeze-out time is dependent on density, so the diffuse outer region of the cloud remains abundant in gas for about an order of magnitude longer. We find that fairly small amounts of diffusive mixing can delay freeze-out at the centre of the model cloud for a time up to an order of magnitude greater than without diffusion, due to material diffusing inward from the edges of the cloud. The gas-phase lifetime of the cloud core can thus be increased by up to an order of magnitude or more by this process. We have run three different grain models with various diffusion coefficients to investigate the effects of changing the sticking parameters.