Kengo Moribayashi

Spherically symmetric models for x-ray damage and the movement of electrons produced in non-spherically symmetric targets such as bio-molecules

This paper develops spherically symmetric models as well as a more accurate model for the calculation of the damage and the movement of free and quasi-free electrons which are produced from the irradiation of x-ray free electron lasers (XFELs). The behaviour of free and quasi-free electrons is studied for targets with various shapes such as spheres and ellipsoids by treating the space distribution of free and quasi-free electrons. Furthermore, the limits of the application of spherically symmetric models to various shapes are discussed. The spherically symmetric model developed here is also applied to a bio-molecule. The results obtained are useful for the analysis of the three-dimensional structures of large bio-molecules in the experiments of XFELs.

Application of XFEL to the measurement of x-ray flux irradiating bio-molecules by using x-ray emission from hollow atoms produced from multiple x-ray absorption

We propose the measurement of x-ray flux irradiating bio-molecules by the theoretical treatment of atomic processes together with multiple x-ray absorption. This measurement is useful for the application of x-ray free electron lasers to the measurement of diffraction patterns of bio-molecules, which is indispensable for the study of their three-dimensional structure. The charge numbers of atoms such as C, N, O in bio-molecules, which appear in the fluorescent x-ray spectroscopy from singly inner-shell ionized atoms and hollow atoms, may inform us of the x-ray flux. Furthermore, it is found that the ratio of the number of fluorescent x-ray photons from the hollow atoms to that from the singly inner-shell ionized atoms is in proportion to the x-ray flux irradiating these atoms. This ratio may also be used for the measurement of the x-ray flux.

Incorporation of the effect of the composite electric fields of molecular ions as a simulation tool for biological damage due to heavy-ion irradiation

This paper presents a theoretical study of the DNA damage due to the effect of the composite electric fields of H{sub 2}O{sup +} ions produced from the irradiation of a heavy ion onto a cell. A model for atomic and molecular processes in strong electric fields is developed. It is found that the composite electric fields increase the number of events of electron-impact ionization processes. This may promote DNA damage.

Simulation and experiments of the laser induced breakdown of air for femtosecond to nanosecond order pulses

3D + 1 dimensional simulations and experimental results for the laser induced breakdown of air are presented. The simulations include the laser propagation, multi-photon and impact ionization and heating of the electrons using accurate atomic and molecular data. For laser pulses of duration from 100 fs to 1 ns mechanisms for the breakdown of air based on the pulse duration and intensity ranging from optical field ionization to electron impact ionization are found. The laser energies at which the breakdown occurs are found to be in good agreement with experimental results.

The gain distribution of the transient collisional excited X-ray lasers

Abstract An atomic kinetics model of an electron collisional excited X-ray laser is developed, and the spatial and temporal evolution of the soft X-ray gain is investigated. The calculation of the gain agrees with experiment for the transient collisional excited (TCE) Ni-like Ag laser ( λ=139 A ) pumped by two 100 ps laser pulses. The mechanism of producing gain in the ionizing plasma is discussed. The calculation is applied to the optimization of the gain. It is found that higher gain can be obtained by pumping a thin foil target with 2 ps laser pulses. The saturation intensity of the X-ray lasers is also investigated through the analysis of the detailed atomic processes of the upper laser level.

Development of the radial dose distribution function relevant to the treatment planning system for heavy particle cancer therapy

This paper presents a study of the radial dose due to the irradiation of a heavy ion, through simulations using a selection of types of atomic and molecular (AM) data. In order to widely spread our radial dose simulation results, a simple radial dose distribution function is proposed. This required a comparison of our results with the available conventional radial dose distributions. It is also shown that the treatment planning system for heavy particle cancer therapy is expected to become one of the most important applications of AM data to biological and medical science.

X-ray emission from inner-shell ionization of Ne-like ions

We study the X-ray emission from the inner-shell states of S and Fe ions excited by black-body radiation. At a low temperature, the X-ray intensities from inner-shell excited states are smaller than that of Heα. However, at high temperature, both are almost the same. From this trend, we may understand the temperature of the black-body radiation. This may be applied to the analysis of the X-ray emission from X-ray binary stars. Namely, the atomic data along with the inner-shell ionization processes may be useful for astrophysics as well as inner-shell ionization X-ray lasers.

Formation mechanisms of multi-charged Kr ions through 2p shell photoionization using a coincidence technique

Multiply charged Kr ions have been measured using monochromatized undulator radiation combined with a coincidence technique. Above the L3 ionization threshold, photoionization has yielded multi-charged ions in a variety of charge states, which range mainly 3+ through 7+. The charge state distribution obtained using a pulse field technique is close to the spectra previously measured with different techniques, and is slightly different from that obtained by calculation. The coincidence measurements between multi-charged ions and energy-selected Auger electrons have disentangled complex decay processes. The Auger final states formed through L3M45M45 decays turn significantly into Kr4+ and those through L3M23M45 decays generate Kr5+ mainly. The Auger decays of L3M23M23 types yield Kr6+ dominantly. These findings are consistent with the consideration of energy levels of Kr ions; higher energy states turn into more highly-charged ions.

Theoretical study of the application of hollow atom production to the intensity measurement of short-pulse high-intensity x-ray sources

We perform a theoretical study for the measurement of short-pulse high-intensity x-ray sources through the x-ray emission processes from multi-inner-shell excited states (1s22s22pk3s23p2, k = 1–4) and hollow atoms (1s22s23s23p2) of Si. We discuss the effect of weak-intensity long-pulse x-rays mixed with high-intensity short-pulse x-rays and the ratio of the x-ray emission from multi-inner-shell excited states with that from hollow atoms.

X-ray emission from hollow atoms produced by collisions of multiply charged ions with a solid

The X-ray emission from hollow atoms produced by collisions of multiply charged ions accelerated by a short pulse laser with a solid or foil is studied theoretically. The possibility of obtaining a high conversion efficiency X-ray source in an ultrafast atomic process (∼ 1 fs) is demonstrated using the multistep-capture-and-loss (MSCL) model. Such an X-ray source has a clear advantage for the spectral range around a few kiloelectron volts over the conventional K α X-ray source. Namely, the number of X-ray photons increases as the laser energy becomes larger and could reach 3 X 10 11 photons for a laser energy of about 10 J.