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Journal Articles

Investigations of relativistic laser plasma from micron-sized Ar clusters

Fukuda, Yuji; Yamakawa, Koichi

Progress in Ultrafast Intense Laser Science II, p.231 - 251, 2007/00

To better understand a fundamental aspect of the laser cluster interaction, we have carried out systematic investigations of X-ray radiation properties of high-density and high-temperature cluster plasma, created by the action of superintense laser irradiation. The interrelationship between the X-ray radiation properties and ion kinetic energies has been for the first time examined by the simultaneous measurements of X-ray radiation spectra and ion energy spectra. Time scale and mechanism of X-ray emission process have been discussed based on a time-dependent plasma kinetics model. Moreover, in order to demonstrate the practical capability of X-rays thus produced, the pulse X-ray diffraction has been examined from Si crystal with this source.

Journal Articles

Yields of strand breaks and base lesions induced by soft X-rays in plasmid DNA

Yokoya, Akinari; Fujii, Kentaro; Ushigome, Takeshi; Shikazono, Naoya; Urushibara, Ayumi; Watanabe, Ritsuko

Radiation Protection Dosimetry, 122(1-4), p.86 - 88, 2006/12

 Times Cited Count:10 Percentile:38.25(Environmental Sciences)

We have studied yields of DNA damages induced by soft X-rays obtained from a conventional soft X-ray machine in a LET region between $$gamma$$-rays and ultrasoft X-rays. Practically soft X-rays with a broad energy spectrum emitted from a target of heavy metal, such as tungsten, have been widely used not only for radiobiological experiments but also for medical application such as mammography. Radiation weighting factors for these soft X-rays have been assigned to be 1 by ICRP. However, the fraction of a large number of low energy photons in the spectrum (below several tens keV) provided by bremsstrahlung is expected to be more effective for DNA damage induction than $$gamma$$-rays since low energy photo- and Auger electrons predominantly ejected in consequence of a photoelectric effect can produce dense clusters of ionization/excitation on DNA molecules. We have examined the yield of DNA strand breaks induced by white soft X-rays (150 kVp, tungsten target). Yields of base lesions revealed by base excision repair enzymes will be also presented.

Journal Articles

Replica symmetry breaking for the Ising spin glass within cluster approximations

Yokota, Terufumi

Physica A, 363(2), p.161 - 170, 2006/03

 Times Cited Count:6 Percentile:55.94(Physics, Multidisciplinary)

Within a class of cluster approximations, the Ising spin glass model on a d-dimensional hypercubic lattice is solved near the spin glass transition temperature. Spin glass order parameter function and Almeida-Thouless line are obtained.

Journal Articles

Structure and dynamics of cluster plasmas created by ultrashort intense laser fields

Fukuda, Yuji; Kishimoto, Yasuaki; Masaki, Tomohiro*; Yamakawa, Koichi

Physical Review A, 73(3), p.031201_1 - 031201_4, 2006/03

 Times Cited Count:31 Percentile:20.26(Optics)

An ultrashort, intense laser-cluster interaction and a resultant structure formation are investigated in detail by employing a particle code including relaxation and ionization processes. In addition to a laser-induced polarization field, we have found that an ambipolar radial electric field and an internal/external sheath field play a key role in a disassembling dynamics of the cluster. Electrons and ions show a complex behavior leading to a prominent dip structure in electron energy distribution and a double structure in ion density and energy distributions for higher charge states.

Journal Articles

Structure analysis of carbon cluster ion using coulomb explosion

Chiba, Atsuya; Saito, Yuichi; Narumi, Kazumasa

JAEA-Review 2005-001, TIARA Annual Report 2004, p.343 - 345, 2006/01

Recently, we have gained interesting results on the interaction between a swift cluster ion and a solid in TIARA. For the elucidation of these interactions and the physical effects, it is very important to grasp the structure of the cluster. For this purpose, a measurement system based on Coulomb explosion imaging (ECI) for analyzing the structure of small carbon clusters has been developed. The ECI technique involves the foil-induced dissociation of a swift cluster by electron stripping. As our first step of the investigation on the carbon cluster structure, the preliminary experiment was carried out on the structure dependence on the average charge state of atoms that composed a cluster passing through a thin foil.The result shows the same tendency as a calculated theoretical value.

Journal Articles

Desorption of cluster ions from frozen gases following high-density electronic excitation

Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao

Surface Science, 593(1-3), p.324 - 330, 2005/11

 Times Cited Count:6 Percentile:67.87(Chemistry, Physical)

no abstracts in English

Journal Articles

Clustered DNA damage induced by ionizing radiaton

Yokoya, Akinari; Shikazono, Naoya; Urushibara, Ayumi; Fujii, Kentaro; Akamatsu, Ken; Watanabe, Ritsuko

Hoshasen Seibutsu Kenkyu, 40(2), p.168 - 184, 2005/06

Ionizing radiation causes modifications in a DNA molecule depending on the characteristic tack-structure in which two or more isolated lesions arise in a few nm scale (1 or 2 helical turn of DNA), known as "clustered DNA damage". These clustered DNA damages could be distinct from those by reactive oxygen species (ROS) endogenously induced on their severity of induction of biological effects such as mutation. However, the studies on the nature and repair mechanism of clustered DNA damage have still been behind because of the technical difficulties on determination of the chemical structure and yield. This article reviews some experimental evidences of the clustered DNA damages in this research field, as well as our recent progress on the studies on the clustered DNA damages using both molecular biological techniques and synchrotron spectroscopic method.

Journal Articles

Measurement of carbon cluster charge state passing through thin foils using a luminance plate

Chiba, Atsuya; Saito, Yuichi; Tajima, Satoshi

Nuclear Instruments and Methods in Physics Research B, 232(1-4), p.32 - 36, 2005/05

 Times Cited Count:9 Percentile:44.77(Instruments & Instrumentation)

The structure of cluster ion may be important parameter for resolution of physical effect and interaction with cluster ion and solid. In this paper, we report a Coulomb explosion imaging of the constituent atoms of a swift carbon cluster (Cn, n=2, 3 and 6) passing through a thin foil and their average charge state that related with the structure of the cluster. The experimental setup is based on the 3MV TANDEM accelerator at the JAERI Takasaki. The cluster ion beam is pulsed by electrical deflection plates and an aperture. A few clusters pass trough the thin foil during 1 second, and the resulting are collected by the luminance plate detector. The average charge state was shown an almost same tendency as calculate theoretical value.

Journal Articles

Endohedral clusterization of ten water molecules into a "molecular ice" within the hydrophobic pocket of a self-assembled cage

Yoshizawa, Michito*; Kusukawa, Takahiro*; Kawano, Masaki*; Ohara, Takashi; Tanaka, Ichiro*; Kurihara, Kazuo; Niimura, Nobuo*; Fujita, Makoto*

Journal of the American Chemical Society, 127(9), p.2798 - 2799, 2005/03

 Times Cited Count:245 Percentile:2.61(Chemistry, Multidisciplinary)

An adamantanoid (H$$_{2}$$O)10 cluster is formed within the hydrophobic cavity of a self-assembled coordination cage. This cluster is termed "molecular ice" because it is the smallest unit of naturally occurring Ic-type ice. X-ray structural analysis, coupled with neutron diffraction study, reveals that the molecular ice is formed not by a simple space-filling effect but by efficient molecular recognition within the cage via H$$_{2}$$O:...pi interaction.

Journal Articles

Hardening of Fe-Cu model alloys induced by electron irradiation and neutron irradiation

Tobita, Toru; Aizawa, Kazuya; Suzuki, Masahide; Iwase, Akihiro*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 3(4), p.331 - 339, 2004/12

Nevertheless, there is a possibility that $$gamma$$-ray induces embrittlement more efficiently than fast neutron, the irradiation effect of $$gamma$$-ray has not been fully clarified. Comparative experiments on irradiation hardening by 2.5MeV electron irradiation for the purpose of $$gamma$$-ray irradiation and neutron irradiation were performed to the Fe-Cu model alloys. We obtained the dose dependence and the temperature dependence on irradiation induced hardening. The growth of Cu clusters with increase in irradiation dose was confirmed by the small angle neutron scattering measurements. Although the differences in hardening between electron and neutron irradiations were very small on a displacement-per-atom (dpa) basis, the electron irradiation hardening initiated slightly earlier than the neutron. The growth of Cu clusters with increase in irradiation dose was the principal cause of hardening. The present results suggested that, from an engineering point of view, both the $$gamma$$-ray induced and neutron induced hardening can be well scaled by using dpa.

Journal Articles

CARS study of deuterium clusters stabilized in solid helium

Gordon, E. B.*; Kumada, Takayuki; Ishiguro, Masazumi; Aratono, Yasuyuki

Journal of Experimental and Theoretical Physics, 99(4), p.776 - 783, 2004/10

The solid Deuterium clusters for the first time isolated in a matrix of solid Helium have been investigated at T = 1.3K and P = 3 MPa by CARS (Coherent anti-Stokes Raman spectroscopy) technique. The Q1(J=0) and Q1(J=1) lines intensity, shape and positions have been studied as the functions of ortho- para content in the solid, as well as of clusters size. The strong effect of Raman scattering cross section sensitivity to the molecular environment nuclear spin state has been found in CARS; the ratio of probabilities for the scattering by para (J=1) and ortho (J=0) deuterium being equal to 1 in a gas is as high as 10,000 in nearly pure o-D2, whereas it is about 50 in spontaneous Raman scattering. This effect has been shown to give rise starting from cluster size corresponding to the phonon band onset.

Journal Articles

Study of the oxidation for Si nanostructures using synchrotron radiation photoemission spectroscopy

Nath, K. G.; Shimoyama, Iwao; Sekiguchi, Tetsuhiro; Baba, Yuji

Applied Surface Science, 234(1-4), p.234 - 239, 2004/07

 Times Cited Count:6 Percentile:64.23(Chemistry, Physical)

Here we report oxidization properties of Si nanostructures grown on graphite. Si 1s X-ray photoemission spectra using synchrotron radiation are used in order to understand the oxidization pathways. Several Si films, such as 0.4, 2, 5.5 & Aring; were grown on highly oriented pyrolitic graphite (HOPG). In the case of a 0.4 & Aring; Si on HOPG, where different types of Si nanostructures in the form of nanoclusters are present, oxygen reactivity is nearly zero. In contrast, the thick film (5.5 & Aring;), where a bulk-type phase is present, shows a higher degree of reactivity. The results are discussed on the basis of nanostructure geometry, number of constituting Si atoms and cluster size.

Journal Articles

Generation of X-rays and energetic ions from superintense laser irradiation of micron-sized Ar clusters

Fukuda, Yuji; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki; Kishimoto, Yasuaki; Yamakawa, Koichi; Faenov, A. Y.*; Magunov, A. I.*; Pikuz, T. A.*; et al.

Laser and Particle Beams, 22(3), p.215 - 220, 2004/07

High resolution K-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters have been measured with an intensity above 10$$^{19}$$ W/cm$$^2$$ and a pulse duration of 30 fs. The total photon flux of 2$$times$$10$$^8$$ photons/pulse was achieved for He$$_{alpha1}$$ resonant line of Ar ($$lambda$$=3.9491 AA , 3.14 keV). In parallel with X-ray measurements, energy distributions of emitted ions have been measured. The multiply-charged ions with kinetic energies up to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoric heating of clusters and shift the ion balance towards the higher charge states, which enhances both the X-ray line yield of the He-like argon ion and the ion kinetic energy.

Journal Articles

X-ray radiation of clusters irradiated by ultrafast, high-intensity laser pulses

Fukuda, Yuji; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki; Kishimoto, Yasuaki; Yamakawa, Koichi; Faenov, A. Y.*; Magunov, A. I.*; Pikuz, T. A.*; et al.

Laser-Generated & Other Lab. X-Ray & EUV Sources (Proceedings of SPIE Vol.5196), p.234 - 243, 2004/00

High resolution X-ray emission spectra of plasma created by laser irradiation of rare-gas (Ar, Kr, Xe) clusters have been measured at laser intensities over 10$$^{19}$$ W/cm$$^2$$ and 30-fs pulse duration. To make these measurements possible, in addition to the effort to decrease a prepulse intensity using Pockels cell switches, micron-size clusters were produced using a specially designed conical nozzle. The Boltzmann equation and a detailed collisional radiative model are solved simultaneously as a function of time to model the time integrated X-ray spectra of the transient plasma. The results are quantitatively in good agreement with the experimentally observed X-ray emission spectra of Ar clusters.

Journal Articles

Time-dependent Boltzmann kinetic model of X-rays produced by ultrashort-pulse laser irradiation of argon clusters

Abdallah, J. Jr.*; Csanak, G.*; Fukuda, Yuji; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki; Yamakawa, Koichi; Faenov, A. Y.*; Magunov, A. I.*; et al.

Physical Review A, 68(6), p.063201_1 - 063201_8, 2003/12

 Times Cited Count:52 Percentile:11.46(Optics)

The Boltzmann Equation and a detailed collisional radiative model are solved simultaneously as a function of time to model the time integrated X-ray spectra of the transient plasma produced by a high intensity ultrafast laser source. The results are in agreement with highly resolved F-like to He-like K-shell emission spectra recorded recently during ultrashort laser experiments with argon cluster targets in Japan.

Journal Articles

Chemical-state analysis for low-dimensional Si and Ge films on graphite

Nath, K. G.; Shimoyama, Iwao; Sekiguchi, Tetsuhiro; Baba, Yuji

Journal of Applied Physics, 94(7), p.4583 - 4588, 2003/10

 Times Cited Count:15 Percentile:45.62(Physics, Applied)

no abstracts in English

Journal Articles

X-ray study of microdroplet plasma formation under the action of superintense laser radiation

Fukuda, Yuji; Yamakawa, Koichi; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki; Abdallah, J. Jr.*; Csanak, G.*; Faenov, A. Y.*; Magunov, A. I.*; et al.

JETP Letters, 78(3), p.115 - 118, 2003/08

 Times Cited Count:28 Percentile:22.12(Physics, Multidisciplinary)

We have measured the X-ray emission spectra of a plasma generated by laser radiation with an intensity above 10$$^{19}$$ W/cm$$^2$$ and a pulse duration of 30 fs acting uon an argon jet target with a large aboundance of micron-sized clusters. The time variation of the X-ray yeild from various multiplicities, calculated within the framework of a nonstationary kinetic model, shows a good qualitative agreement with the experimental time-integrated spectrum.

Journal Articles

Optimized energetic particle emissions from Xe clusters in intense laser fields

Fukuda, Yuji; Yamakawa, Koichi; Akahane, Yutaka; Aoyama, Makoto; Inoue, Norihiro*; Ueda, Hideki; Kishimoto, Yasuaki

Physical Review A, 67(6), p.061201_1 - 061201_4, 2003/06

 Times Cited Count:55 Percentile:10.56(Optics)

We have probed the interaction of intense laser fields with Xe clusters by measuring the energy and charge state distributions of emitted ions and electrons using ultrafast 20 fs pulses. This work demonstrates that the energetic particle emissions from laser-cluster interactions can be optimized by manipulating the character of ultrafast laser pulses, i.e. pulse duration and sign of chirp.

Journal Articles

Effects of hydration on the induction of strand breaks, base lesions, and clustered damage in DNA films by $$alpha$$-radiation

Yokoya, Akinari; Cunniffe, S. M. T.*; Stevens, D. L.*; O'Neill, P.*

Journal of Physical Chemistry B, 107(3), p.832 - 837, 2003/01

 Times Cited Count:25 Percentile:41.64(Chemistry, Physical)

no abstracts in English

Journal Articles

Size-selective extended X-ray absorption fine structure spectroscopy of free selenium clusters

Nagaya, Kiyonobu*; Yao, Makoto*; Hayakawa, Tetsuichiro*; Omasa, Yoshinori*; Kajihara, Yukio*; Ishii, Masashi*; Katayama, Yoshinori

Physical Review Letters, 89(24), p.243401_1 - 243401_4, 2002/12

 Times Cited Count:15 Percentile:34.79(Physics, Multidisciplinary)

Recently, we proposed a new method for the size-selective EXAFS(Extended X-ray absorption fine structure) of neutral-free culsters, in which not only the X-ray absorption process but also the deexitation process are utilized as the structural information. In order to verify this method experimentally, we have developed the synchronous measurements of EXAFS and photoelectron photoion coincidence and carried them out for a Se cluster beam by utilizing the third-generation intense X-ray source. The EXAFS spectra for Se small clusters have been obtained and compared critically with theoretical predictions.

75 (Records 1-20 displayed on this page)