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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

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ISSN (Print) 0168-583X
Published by Elsevier

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Finite Sum Expressions for Elastic and Reaction Cross Sections
- Abstract: Publication date: Available online 16 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Charles M. Werneth , Khin Maung Maung , Lawrence R. Mead , Steve R. Blattnig
  Nuclear cross section calculations are often performed by using the partial wave method or the Eikonal method through Glauber theory. The expressions for the total cross section, total elastic cross section, and total reaction cross section in the partial wave method involve infinite sums and do not utilize simplifying approximations. Conversely, the Eikonal method gives these expressions in terms of integrals but utilizes the high energy and small angle approximations. In this paper, by using the fact that the l th partial wave component of the T-matrix can be very accurately approximated by its Born term, the infinite sums in each of the expressions for the differential cross section, total elastic cross section, total cross section, and total reaction cross section are re-written in terms of finite sums plus closed form expressions. The differential cross sections are compared to the Eikonal results for 16 O + 16 O , 12 C + 12 C , and p + 12 C elastic scattering. Total cross sections, total reaction cross sections, and total elastic cross sections are compared to the Eikonal results for 12 C + 12 C scattering.
  
  PubDate: 2013-05-19T08:04:19Z
Stopping powers of LiF thin films deposited onto self-supporting Al foils for swift protons
- Abstract: Publication date: Available online 16 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Smail Damache , Djamel Moussa , Saâd Ouichaoui
  The energy losses of ∼ (0.273_3.334) MeV protons in LiF thin films deposited by vacuum evaporation onto self-supporting Al foils have been measured using the transmission method. The thicknesses of selected and used LiF/Al target samples were accurately determined via systematic energy loss measurements for alpha particles from a very thin mixed 241Am/239Pu/233U radioactive source. The samples were investigated in detail for their stoichiometry and their impurity contents by backscattering Rutherford spectrometry and nuclear reaction analysis. Then, LiF stopping powers have been determined with overall relative uncertainty of less than 2.7% arising mainly from errors in the determination of target sample thicknesses. These S(E) data are reported and discussed in comparison to previous experimental data sets from the literature and to values calculated by the Sigmund-Schinner binary collision stopping theory both for molecular LiF, and for the LiF compound assuming Bragg-Kleeman’s additivity rule. Our S(E) data show to be in excellent agreement with the latter theory for molecular LiF over the whole proton energy range explored, which supports the use of modified electronic Hydrogen wave functions for evaluating atomic shell corrections in the case of low-Z2 target materials. In contrast, they exhibit a slightly increasing deviation from theoretical values derived for the LiF compound with assuming stopping force additivity as the proton energy decreases from E ≈ 400 keV towards lower proton velocities. This deviation in excess relative to experimental data, amounting only up to (at most) ∼2.5%, can be ascribed to strong effects of 2s-state valence electrons of Li atoms within the LiF compound. Besides, the comparison to values calculated by the SRIM-2008 computer code indicates that this program satisfactorily accounts for our S(E) data above E ≈ 1.30 MeV but underestimates them with substantially increasing deviations (up to ∼11%) towards lower proton velocities where the Bragg-Kleeman additivity rule therefore appears to be inapplicable.
  
  PubDate: 2013-05-19T08:04:19Z
Resonant Ionization Laser Ion Source (RILIS) Off-Line Developments on Ga, Al and Ca
- Abstract: Publication date: Available online 17 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): R. Li , J. Lassen , A. Teigelhöfer , J.P. Lavoie , P. Bricault , O. Chackakova , J. Meissner , Y. Zlateva
  The Resonant Ionization Laser Ion Source (RILIS) is an element selective, highly efficient and versatile tool for generation of radioactive ion beams at on-line mass separator facilities. Parallel to TRIUMF’s on-line RILIS at the Isotope Separator and ACcelerator (ISAC) facility, an off-line Laser Ion Source test stand (LIS STAND) is operated for systematic laser resonance ionization spectroscopy, ionization scheme and ion source development. Three titanium sapphire (Ti:Sa) lasers optionally equipped with harmonic frequency generation units are used to resonantly step-wise excite and ionize elements of interest. A grating tuned Ti:Sa laser allows continuous laser wavelength scans of up to Δ ≈ 200 nm. With this laser inventory and the LIS STAND, atomic Rydberg series and auto-ionizing levels can systematically be studied. The LIS STAND has been in use since 2009 and so far the spectroscopy on Ga, Al and Ca has been performed. The development of efficient laser resonant ionization schemes, their investigation and comparison using the LIS STAND are discussed.
  
  PubDate: 2013-05-19T08:04:19Z
Study of spatial resolution of YAG:Ce cathodoluminescent imaging screens
- Abstract: Publication date: Available online 18 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Petr Schauer , Jan Bok
  The aim of this paper is to find spatial resolution of YAG:Ce single crystal cathodoluminescent imaging screens at primary electron energies in the range from 20 to 100keV using theoretical simulation as well as the experimental method. Calculations have been based on the MC model for energy distribution of excited electrons. Measurement of the spatial resolution was realized using the sharp edge projection method. As the projection object, the silicon single crystal plate with the hole made by the anisotropic etching was prepared and used. The edge of this object was examined at the magnification of up to 125000x. For the edge projection method, the experimental system with the screen specimen cartridge and with the light-microscopic module using the magnifying objective and the CCD camera has been constructed and used. The simulated as well as experimental results have been processed and are presented in the form of line spread function (LSF). The resulted image qualities were quantified using modulation transfer function (MTF). Finally, the spatial resolutions of YAG:Ce single crystal imaging screens were determined as the number of lines per mm for the contrast of 50% and primary electron beam energies of 20, 60 and 100 keV.
  
  PubDate: 2013-05-19T08:04:19Z
Deceleration of Ar9+ ions within a tapered glass capillary
- Abstract: Publication date: 15 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 305
  Author(s): M. Kreller , G. Zschornack , U. Kentsch
  We report experimental studies of the deceleration of Ar9+ ions within a single tapered glass capillary with an inlet diameter of 1mm, an outlet diameter of 0.15mm and a length of 45mm. In the experiments we have chosen an incident ion energy of q ·8.5keV (q – ion charge state). The influence of the deceleration potential between entrance and exit of the glass capillary on the intensity of the transmitted ion beam was measured. We detected a transmission of the ion beam up to a deceleration potential of 7kV. Hence, the ion beam was decelerated and compressed to a diameter of 150μm without using any additional decelerating lens systems.
  
  PubDate: 2013-05-19T08:04:19Z
Electronic stopping power of H and He in Al and LiF from first principles
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): M. Ahsan Zeb , J. Kohanoff , D. Sánchez-Portal , Emilio Artacho
  Non-linearities in the electronic stopping power of light projectiles in bulk Al and LiF are addressed from first principles using time-evolving time-dependent density functional theory. In the case of Al, the agreement of the calculations with experiments for H and He projectiles is fair, but a recently observed transition for He from one value of the electronic friction coefficient to a higher value at v ∼ 0.3 a.u. is not reproduced by the calculations. For LiF, better accuracy is obtained as compared with previously published simulations, albeit the threshold remains overestimated.
  
  PubDate: 2013-05-19T08:04:19Z
Phase-field simulations of intragranular fission gas bubble evolution in UO2 under post-irradiation thermal annealing
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Yulan Li , Shenyang Hu , Robert Montgomery , Fei Gao , Xin Sun
  Fission gas bubbles are one of the evolving microstructures that affect thermal mechanical properties, such as thermal conductivity, gas release, volume swelling, and cracking, in operating nuclear fuels. Therefore, fundamental understanding of gas bubble evolution kinetics is essential to predict the thermodynamic property and performance changes of fuels. In this work, a generic phase-field model was developed to describe the evolution kinetics of intragranular fission gas bubbles in UO2 fuels under post-irradiation thermal annealing conditions. Free energy functional and model parameters are evaluated from atomistic simulations and experiments. Critical nucleus size of gas bubbles and gas bubble evolution were simulated. A linear relationship between logarithmic bubble number density and logarithmic mean bubble diameter was predicted, which is in good agreement with experimental data.
  
  PubDate: 2013-05-19T08:04:19Z
Computer simulation of internal electron emission in ion-bombarded metals
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): S. Hanke , A. Duvenbeck , C. Heuser , B. Weidtmann , D. Diesing , M. Marpe , A. Wucher
  We present a computer simulation study of internal electron emission in ion-bombarded metal–insulator–metal (MIM) junctions. The computational approach consists of (i) a molecular dynamics part describing the particle kinetics upon projectile impact, (ii) the computation of kinetic electronic excitation as well as its transport and (iii) a thermionic model to calculate the flux of electrons from the top electrode to the bottom electrode of the MIM. The results are compared to recent experiments and discussed in terms of different transport models for the description of hot electron propagation in metals.
  
  PubDate: 2013-05-19T08:04:19Z
Computer simulation of cluster impact induced electronic excitation of solids
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): B. Weidtmann , S. Hanke , A. Duvenbeck , A. Wucher
  We present a computational study of electronic excitation upon bombardment of a metal surface with cluster projectiles. Our model employs a molecular dynamics (MD) simulation to calculate the particle dynamics following the projectile impact. Kinetic excitation is implemented via two mechanisms describing the electronic energy loss of moving particles: autoionization in close binary collisions and a velocity proportional friction force resulting from direct atom–electron collisions. Two different friction models are compared with respect to the predicted sputter yields after single atom and cluster bombardment. We find that a density dependent friction coefficient leads to a significant reduction of the total energy transferred to the electronic sub-system as compared to the Lindhard friction model, thereby strongly enhancing the predicted sputter yield under cluster bombardment conditions. In contrast, the yield predicted for monoatomic projectile bombardment remains practically unchanged.
  
  PubDate: 2013-05-19T08:04:19Z
Stability of vacancy clusters in FeCr alloys: A study of the Cr concentration dependence
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Jesús M. Sampedro , Emma del Rio , María J. Caturla , Alfredo Caro , Magdalena Caro , J. Manuel Perlado
  Fe–Cr based alloys are the leading structural material candidates in the design of next generation reactors due to their high resistance to swelling and corrosion. Despite these good properties there are others, such as embrittlement, which require a higher level of understanding in order to improve aspects such as safety or lifetime of the reactors. The addition of Cr improves the behavior of the steels under irradiation, but not in a monotonic way. Therefore, understanding the changes in the Fe–Cr based alloys microstructure induced by irradiation and the role played by the alloying element (Cr) is needed in order to predict the response of these materials under the extreme conditions they are going to support. In this work we perform a study of the effect of Cr concentration in a bcc Fe–Cr matrix on formation and binding energies of vacancy clusters up to 5 units. The dependence of the calculated formation and binding energy is investigated with two empirical interatomic potentials specially developed to study radiation damage in Fe–Cr alloys. Results are very similar for both potentials showing an increase of the defect stability with the cluster size and no real dependence on Cr concentration for the binding energy.
  
  PubDate: 2013-05-19T08:04:19Z
Stress dependence of oxygen diffusion in ZrO2 film
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Yasunori Yamamoto , Kazunori Morishita , Hirotomo Iwakiri , Yasunori Kaneta
  First principles calculations were performed to evaluate the effect of stress on the diffusion process of oxygen atoms in monoclinic and tetragonal ZrO2. The formation and migration energies of an oxygen vacancy were obtained as a function of applied stress. Our results show that the formation and migration energies increase when the compressive stress is applied, which causes a reduction in the diffusion coefficient of an oxygen atom in ZrO2. This may explain the experimental observation that the oxide film grows in proportion to the cubic root of time.
  
  PubDate: 2013-05-19T08:04:19Z
Reaction kinetic analysis of damage rate effects on defect structural evolution in Fe–Cu
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): T. Yoshiie , Q. Xu , K. Sato
  In Fe–Cu alloys, Cu precipitates are formed during high-energy particle irradiation. If there exists energetic binding between vacancies and Cu atoms, vacancy clusters (voids) are formed in precipitates at an initial stage of irradiation, separate from voids in the matrix, because of the migration of Cu atoms with vacancies. In this paper, the damage rate dependence on the formation and annihilation of voids in the precipitates and in the matrix is simulated by reaction kinetic analysis. The initial formation of voids at precipitates, the annihilation of them with an increased dosage and new formation of voids in the matrix are simulated, and the results are compared with the experiments. In a high damage rate of 3.3×10−7 dpa/s, the formation of voids in Cu precipitates is not significant, but the formation of voids in the matrix is dominant, different from those in a low damage rate of 1.5×10−10 dpa/s.
  
  PubDate: 2013-05-19T08:04:19Z
Energetics of radiation defects in Fe-based austenitic alloys: Atomic scale study
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): A. Bakaev , D. Terentyev , X. He , E.E. Zhurkin
  Energetics of typical radiation defects observed in austenitic stainless steel of 304L type has been characterized in the model FeNi10Cr20 alloy by means of atomistic simulations employing a set of interatomic potentials specially derived to reproduce main features of 304L steel. The following defects have been considered: dislocation loops of both interstitial and vacancy nature, stacking fault tetrahedron, perfect loops and voids. The formation energy of these defects has been calculated at 0K and the obtained results have been compared with the prediction of the elasticity theory. A good agreement has been found in all the cases except for the hexagonal Frank loop, whose sides have splitted into 1/6〈112〉 partial dislocations, thus lowering the total formation energy. High temperature annealing, performed using molecular dynamics simulations, has proven that the considered defects are thermally stable in the temperature range 300–1200K.
  
  PubDate: 2013-05-19T08:04:19Z
Molecular dynamics study of polystyrene bond-breaking and crosslinking under C60 and Arn cluster bombardment
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Bartlomiej Czerwinski , Zbigniew Postawa , Barbara J. Garrison , Arnaud Delcorte
  Molecular dynamics computer simulations are used to elucidate the bond-breaking and crosslinking processes induced by 2.5keV C60 and Arn cluster bombardment in an amorphous sec-butyl-terminated polystyrene sample. The obtained results indicate that replacement of C60 by Ar18 or Ar60 projectiles leads to the decrease of the number of broken bonds and, hence, to the decrease of formation of new intra- and intermolecular (crosslinking) bonds. When the number of atoms in the Arn cluster is increased from 60 to 250 or more, the total number of broken bonds and the total number of newly created bonds reach a zero value. Additional comparison to the case of a fullerite crystal reveals that the change of material properties leads to almost 7.5-fold reduction of the efficiency of the crosslinking process.
  
  PubDate: 2013-05-19T08:04:19Z
Ab initio modelling of vacancy–solute dragging in dilute irradiated iron-based alloys
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Luca Messina , Zhongwen Chang , Pär Olsson
  The formation of solute–defect nanoclusters in RPV steels is the main cause of radiation induced embrittlement. Solute atoms may diffuse in the alloy by a vacancy drag mechanism, depending on the strength of interaction with point defects. A multifrequency model based on ab initio computed migration barriers was applied in order to investigate the possibility of solute drag in iron-based bcc binary alloys containing Ni, Cr, Cu or Mn, and the obtained solute diffusion coefficients were compared with previous experiments. The results show that Ni is expected to be dragged at temperatures below approximately 900K, while Cr and Mn are not involved in the dragging mechanism. As for Cu, the results are controversial because the computed migration barriers are strongly affected by the particular choice of the ab initio method.
  
  PubDate: 2013-05-19T08:04:19Z
First-principles calculations of (Y, Ti, O) cluster formation in body centred cubic iron-chromium
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Antoine Claisse , Pär Olsson
  In the present work, the ab initio parametrization necessary for a Monte Carlo study of the (Y, Ti, O) clusters in a FeCr matrix is done. The cohesive, binding and migration energies of all the solutes have been calculated in the dilute limit in the framework of density functional theory. The special case of the strong interaction between an Y atom and a vacancy has been considered. In the dilute limit, Cr is transparent with respect to Y, Ti, O or vacancies. On the contrary, Y binds O strongly in 2NN configuration while not in 1NN. Ti binds O in 1NN and 2NN configurations. A vacancy binds strongly with Y and O in 1NN position which is resulting in a low diffusion coefficient for Y. The peculiar case of the binding attraction between two interstitial oxygen atoms has been studied and is believed to be the main reason for the planar (2D) symmetry of the cluster nuclei. A preferential cluster shape is determined for the early nucleation stage, up to 12 atoms.
  
  PubDate: 2013-05-19T08:04:19Z
Editorial board
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  
  PubDate: 2013-05-19T08:04:19Z
Swift heavy ions irradiation acts as a size filter to Ag nanoparticles embedded in silica glass
- Abstract: Publication date: Available online 18 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Yitao Yang , Chonghong Zhang , Yin Song , Jie Gou , Liqing Zhang , Yancheng Meng , Hengqing Zhang , Yizhun Ma
  The swift heavy ions (SHI) irradiation using as a tool for the ion-beam-shaping technique has attracted much attention in recently years, which can transform spherical metal nanoparticles (Nps) to prolate spheroids, nanorods or nanowires, with the elongation along the beam direction. In the present paper, we show that SHI irradiation can also act as a size filter to Ag Nps embedded in silica glass. In experiment, Ag Nps were introduced into silica glass by Ag ions implantation. Subsequently, 73 MeV Ca ions were used to irradiate the samples contained Ag Nps to different fluences. The direction of incident ions is perpendicular to sample surface. The surface plasmon resonance (SPR) absorbance peak of Ag Nps shifts to short wavelength with increase of irradiation fluence, meanwhile, the full width at half maximum (FWHM) of SPR peak decreases with increase of irradiation fluence. The decrease of FWHM indicates the reduction of Ag Nps size dispersion. TEM results show that Ag Nps smaller than 2.0 nm dissolved during irradiation, only Ag Nps larger than 2.0 nm survive and distribute in a narrow region. High energy Ca ions irradiation seems to act as a size filter. From TEM micrographs the size dispersion of Ag Nps is reduced comparing with that before irradiation, which is consistent with optical results.
  
  PubDate: 2013-05-19T08:04:19Z
Effect of voids on the tensile properties of vanadium nanowires
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Liang Wang , Huiqiu Deng , Shifang Xiao , Wangyu Hu
  Vanadium alloys are one of the candidates for first-wall materials. Due to the impact of high energy neutrons and transmutation helium during a fusion reaction, voids will be formed and the mechanical properties of the first-wall materials will be degraded. It is necessary to investigate the effect of voids on the mechanical behavior of the material. In the present paper, the tensile properties of vanadium nanowires with a void have been studied with molecular dynamics simulations. During a deformation process, the generation of 〈111〉/{112} stacking faults to form twinnings in vanadium nanowires. The void facilitates the nanowire’s rupture and alters the deformation behavior of nanowires. For the nanowire with a void, the twin initiates near the vicinity of the void rather than a random location as in a nanowire without void. Twinning boundaries propagate towards the ends of nanowire until the whole wire transforms from the initial orientation (z-〈001〉) to a new configuration (z-〈110〉) with a rotation of 90° under a tensile stress. The nucleation and growth of the twin is inhibited as void size increases, and the nanowires crack is mainly induced by the disordering of vanadium atoms near the void rather than twinning deformation for large size void. A critical effective cross sectional width is determined for different deformation mechanisms. © 2012 Elsevier Science. All rights reserved
  
  PubDate: 2013-05-19T08:04:19Z
Modelling radiation damage at grain boundaries in fcc Nickel and Ni-based alloy using Long Time Scale Dynamics Techniques
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Zainab Al Tooq , Steven D. Kenny
  The long timescale evolution of radiation damage near grain boundaries (GB) in fcc Ni and a Ni–Cr alloy has been investigated. Molecular dynamics (MD) combined with the on-the-fly kinetic Monte Carlo (otf-KMC) has been used to study the evolution of defects in bulk, Σ3 and Σ5 GB systems resulting from 1keV collision cascades. Results show that both interstitials and vacancies are attracted to GBs, that vacancy and interstitial clustering is observed in the bulk and vacancy clustering in the GB systems.
  
  PubDate: 2013-05-19T08:04:19Z
Conference Photo – COSIRES2012
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  
  PubDate: 2013-05-19T08:04:19Z
Effect of grain boundary on lattice thermal conduction of tungsten revealed by molecular dynamics simulations
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  Author(s): Baoqin Fu , Wensheng Lai , Yue Yuan , Haiyan Xu , Wei Liu
  Tungsten (W) and tungsten-based materials are being considered to be used in the divertor and the first wall as plasma facing materials (PFMs) in the fusion reactor, which requires them to withstand the heat loads. The influence of grain boundaries on the heat flux has been studied by the molecular dynamics (MD) simulations in this paper. Various grain boundaries have been constructed in simulation cells and their lattice thermal conductivities (LTCs) and thermal resistances have been calculated. It turns out that there exist sharp temperature drops across these grain boundaries, indicating that the LTCs near grain boundaries are much smaller than those inside the bulk tungsten. The grain boundary effect on the LTCs of polycrystalline W samples has been analyzed by the combination of MD and finite element results. The results may be potentially helpful for the design of the international thermonuclear experimental reactor (ITER) and the choice of PFMs.
  
  PubDate: 2013-05-19T08:04:19Z
Editorial board
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  
  PubDate: 2013-05-19T08:04:19Z
Special Issue Title Page
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  
  PubDate: 2013-05-19T08:04:19Z
Contents
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  
  PubDate: 2013-05-19T08:04:19Z
Editorial – The 2012 Computer Simulation of Radiation Effects in Solids (COSIRES 2012) international conference
- Abstract: Publication date: 15 May 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 303
  
  PubDate: 2013-05-19T08:04:19Z
Kinetics of post-treatment structural transformations of nitrogen plasma ion immersion implanted polystyrene
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): E. Kosobrodova , A. Kondyurin , D.R. McKenzie , M.M.M. Bilek
  The surface chemistry of a synthetic material in contact with a biological system has a strong influence on the adhesion of proteins to the surface of the material and requires careful consideration in biomedical applications. The structure of plasma immersion ion implantation (PIII) treated polymer and its surface free energy depend on the ion fluence delivered during the treatment and on the time after the PIII treatment. These dependences have been investigated using the example of nitrogen plasma implanted polystyrene (PS). Contact angle measurements, FTIR–ATR spectra and X-ray photoelectron (XPS) spectra were acquired as a function of ion fluence and time after treatment. The results showed a close relationship to the kinetics of free radicals that had been examined in a previous study. The kinetics of oxidation and surface free energy had two stages, one with a characteristic time of several hours and the other with a characteristic time of several days. The concentration of nitrogen-containing groups decreased with time after PIII treatment, partly, due to their release from the PS surface.
  
  PubDate: 2013-05-15T08:05:33Z
Effect of γ-rays irradiation on Mn–Ni ferrites: Structure, magnetic properties and positron annihilation studies
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): H.E. Hassan , T. Sharshar , M.M. Hessien , O.M. Hemeda
  Manganese–nickel ferrites powder with general formula Mn x Ni1− x Fe2O4 (x =0.0, 0.2, 0.4) were synthesized through oxalate precursor route and sintered at 1000°C. The X-ray diffraction (XRD) patterns were measured for the prepared samples to confirm the existence of single-phase structure. The crystallite size was estimated and found to be within the range 125–170nm. To study the radiation effect on the structure and magnetic properties, a representative group of the investigated samples were irradiated by γ-rays of 60Co source with a dose of 310kGy. The XRD spectra were performed for the irradiated samples and compared with that of the pristine samples to estimate changes in the structure. The obtained results showed that the crystallite size increased by a factor of 10–16% after gamma irradiation. The lattice parameter also was increased due to the conversion of Fe3+ (0.64Å) to Fe2+ (0.76Å). The formula of the cation distribution of the ferrites samples was suggested at x =0, 0.2, 0.4 before and after irradiation. The theoretical lattice parameter, sample density and porosity were calculated and compared with that obtained from the experimental data. Good agreement was found between theoretical and experimental structural data which confirms the proposed formula of cations distribution. The hysteresis curves were measured using vibrating sample magnetometer (VSM) for the unirradiated and irradiated samples and the saturation magnetization was estimated. The obtained results showed increase in saturation magnetizations (M s) for all the samples by irradiation due to redistribution of the cations between A and B sites and changing the net magnetic moments. Theoretical calculation of magnetic moments and saturation magnetization using the proposed cations distribution of A and B sites confirmed the experimental results. The positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density after irradiation. The PAL parameters (τ 1, I 1, τ 2, I 2 and mean lifetime) show that the irradiation affects the size and concentration of the vacant type defects. The results reveal that there are some large voids (with radius ranged from 0.28 to 0.38nm and mean value of 0.34±0.04nm in the studied samples). The obtained results indicate the high sensitivity of PALS technique to the enhanced structure changes due to gamma rays irradiation.
  
  PubDate: 2013-05-15T08:05:33Z
Understanding of CO2 interaction with thermally grown SiO2 on Si using IBA depth profiling techniques
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): Geetanjali Deokar , Marie D’Angelo , Emrick Briand , Catherine Deville Cavellin
  Interactions between CO2 and SiO2 films thermally grown on Si have been studied using 18O and 13C as isotopic tracers associated with ion beam analysis (IBA) depth profiling techniques. From secondary ion mass spectrometry (SIMS) measurements no carbon from CO2 is detected in the silica while it is found in Si. These results suggest that CO2 diffuses through the silica. Exchanges of oxygen between CO2 and silica can be observed from 18O to 16O SIMS signals variation. The oxygen concentration depth profiles were determined quantitatively using the narrow resonance near 151keV in the 18O(p,α)15N nuclear reaction (Narrow Resonance Profiling, NRP). We demonstrate that two distinct oxygen exchanges processes co-exist and we determine the diffusion coefficient of the CO2 molecule in the silica at 1100°C.
  
  PubDate: 2013-05-15T08:05:33Z
L-subshell X-ray intensity ratio of Xenon for 6MeV Xe20+ impact on selected targets
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): Xianming Zhou , Yongtao Zhao , Rui Cheng , Xing Wang , Jieru Ren , Yu Lei , Yuanbo Sun , Ge Xu , Yuyu Wang , Guoqing Xiao
  The L-shell X-ray emission of Xenon was measured for 6MeV Xe20+ ions impacting on V, Fe, Ni, Cu and Zn targets. The distinct L-subshell X-rays and the energy shift were observed. The L-shell ionization and the multiple ionization of the outer-shell were investigated. In addition, the relative intensity ratios of Lα1,2 to Lβ1,3,4 and Lβ2,15 were obtained, which approximately decrease linearly with the increasing target atomic number. That was interpreted by considering multiple ionization of the outer-shell electron.
  
  PubDate: 2013-05-11T08:05:36Z
Activation cross-sections of longer lived products of deuteron induced nuclear reactions on ytterbium up to 40MeV
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): F. Tárkányi , F. Ditrói , S. Takács , A. Hermanne , H. Yamazaki , M. Baba , A. Mohammadi , A.V. Ignatyuk
  In the frame of a systematic study of the activation cross-sections of the deuteron induced nuclear reactions, excitation functions of the natYb(d,xn)177,173,172mg,171mg,170,169Lu, natYb(d,x)175,169Yb and natYb(d,x)173,172,168,167,165Tm reactions are studied up to 40MeV, a few of them for the first time. Cross-sections were measured with the activation method using a stacked foil irradiation technique and high resolution γ-ray spectrometry. The experimental data are analyzed and compared to the results of the theoretical model codes ALICE-IPPE, EMPIRE-II and TALYS. From the measured cross-section data integral production yields were calculated. Applications of the new cross-sections are discussed.
  
  PubDate: 2013-05-11T08:05:36Z
Radiation damage induced by swift heavy ions in TiO2 sol–gel films nanocrystallines
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): R. Hazem , M. Izerrouken , A. Sari , S. Kermadi , M. Msimanga , A. Benyagoub , M. Maaza , M. Belgaid , M. Boumaour
  TiO2 films prepared by sol–gel were irradiated with 25.8MeV Cu and 90MeV Xe ions at room temperature under normal incidence. The irradiation with Cu and Xe ions were performed respectively at iThemba labs, South Africa and GANIL, Caen, France. The properties of radiation defects induced in TiO2 nanostructures were investigated using grazing angle X-ray diffraction (GAXRD), atomic force microscopy (AFM) and UV–visible spectrophotometry. From GAXRD analysis, it is found that anatase (101) peak intensity decrease with increasing the fluence and disappear completely above a threshold ion fluence of 5×1012 ion/cm2. This indicates that the crystallinity of the TiO2 film is destroyed upon irradiation due to the amorphous track formation. The track radius estimated from the Poisson’s law is about 2 and 4nm after irradiation with 25.8MeV Cu and 90MeV Xe ions, respectively. According to the AFM analysis, the elaborated TiO2 films are composed of particles with a triangular shape of a size in the range of 200–500nm. It is found that the particle size increases after irradiation with both Cu and Xe ions. In addition, the root-mean-square (RMS) surface roughness for 780nm×780nm area scans decreases exponentially with increasing fluence up to 1013 ions/cm2 in the case of Xe irradiation, but increases drastically above 2.68×1011 ions/cm2 in the case of Cu ion irradiation and reaches a mean value of ∼3nm. The absorption measurements reveal that the optical band gap is not affected by both Xe and Cu ions irradiation.
  
  PubDate: 2013-05-11T08:05:36Z
Distinguishing fissions of 232Th, 237Np and 238U with beta-delayed gamma rays
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): A. Iyengar , E.B. Norman , C. Howard , C. Angell , A. Kaplan , J.J. Ressler , P. Chodash , E. Swanberg , A. Czeszumska , B. Wang , R. Yee , H.A. Shugart
  Measurements of beta-delayed gamma-ray spectra following 14-MeV neutron-induced fissions of 232Th, 238U, and 237Np were conducted at Lawrence Berkeley National Laboratory’s 88-Inch Cyclotron. Spectra were collected for times ranging from 1min to 14h after irradiation. Intensity ratios of gamma-ray lines were extracted from the data that allow identification of the fissioning isotope.
  
  PubDate: 2013-05-11T08:05:36Z
Mechanical stresses and amorphization of ion-implanted diamond
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): R.A. Khmelnitsky , V.A. Dravin , A.A. Tal , M.I. Latushko , A.A. Khomich , A.V. Khomich , A.S. Trushin , A.A. Alekseev , S.A. Terentiev
  Scanning white light interferometry and Raman spectroscopy were used to investigate the mechanical stresses and structural changes in ion-implanted natural diamonds with different impurity content. The uniform distribution of radiation defects in implanted area was obtained by the regime of multiple-energy implantation of keV He+ ions. A modification of Bosia’s et al. (Nucl. Instrum. Meth. B 268 (2010) 2991) method for determining the internal stresses and the density variation in an ion-implanted diamond layer was proposed that suggests measuring, in addition to the surface swelling of a diamond plate, the radius of curvature of the plate. It is shown that, under multiple-energy implantation of He+, mechanical stresses in the implanted layer may be as high as 12GPa. It is shown that radiation damage reaches saturation for the implantation fluence characteristic of amorphization of diamond but is appreciably lower than the graphitization threshold.
  
  PubDate: 2013-05-11T08:05:36Z
Molecular dynamics and Monte Carlo simulations of the sputtering of a nanoporous solid
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): J.F. Rodriguez-Nieva , E.M. Bringa
  We calculate the sputtering induced on a nanoporous material by fast penetrating ions, such as those used for track formation and surface modification, in order to better understand and quantify the ejection and redeposition of atoms in open cell nanofoams. We model the ion-induced sputtering yield from a porous solid using a Monte Carlo approach and compare the results for the sputtering yields, angular and depth distributions of the ejecta, with Molecular dynamics simulations and find good agreement. For certain foam geometries, our simulations predict enhanced sputtering yields compared to the yields from a fully dense solid.
  
  PubDate: 2013-05-07T08:06:55Z
Theoretical investigation on helium incorporation in Ti3AlC2
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): Jingren Xiao , Chenxu Wang , Tengfei Yang , Shuyan Kong , Jianming Xue , Yugang Wang
  Ti3AlC2 known as representing material in MAX phases, has been suggested for next generation nuclear reactor applications for their advantages of thermal/mechanical properties in high temperature and radiation damage resistance. In this paper the helium incorporation properties in Ti3AlC2 are investigated via ab initio methods. The energetically preferred interstitial sites of helium atom in Ti3AlC2 are identified with respect to the chemical potential of each component element. The formation energies of interstitial and substitutional helium atoms are compared to decide the most favorable sites for He in Ti3AlC2 lattice. The calculations show that in most situations helium atom favors the interstitial sites in aluminum layer, whereas it is more likely to substitute on Al sites in the (Ti- and C-rich) environment. Furthermore, the energetics of vacancies were calculated because the presence of single vacancies and bivacancies in the early stage of irradiation damage is thought to modify He behavior in materials to a great extent. These preliminary results lay a solid foundation for further understanding of the underlying mechanisms of helium bubble nucleation and formation in Ti3AlC2.
  
  PubDate: 2013-05-07T08:06:55Z
Measurements of the 11B(d,nγ15.1)12C Differential Cross-Section on Thick and Thin Targets
- Abstract: Publication date: Available online 29 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Kevin W. Cooper , Thomas N. Massey , D.E. Carter , David C. Ingram
  The differential cross-section for the 15.1 MeV gamma ray produced by the 11 B ( d , n γ ) 12 C reaction in a thick natural boron target has been measured for incident deuteron energies ranging from reaction threshold to 5 MeV. Measurements for a thin natural boron target have been carried out over a similar incident deuteron energy range. These results are compared to previous measurements made by Kavanagh (1958) and Kuan (1964). Measurements of the combined thick target yield for the 6.129 , 6.917 , and 7.116 MeV gamma rays from the 19 F ( p , α γ ) 16 O reaction have been carried out on a stopping thickness sulfur hexafluoride gas cell for effective incident proton energies ranging from 1 to 4 MeV as a consistency check on the procedure used for normalization of the detector response function. The results for the 11 B ( d , n γ 15.1 ) 12 C yield a significantly lower cross-section than that previously reported, while the measurements of the 19 F ( p , α γ ) reaction are consistent with previous measurements made by Fessler (2000) and Micklich (2003).
  
  PubDate: 2013-05-03T08:05:20Z
Annealing behavior of impurities and defects in keV Er-implanted ZnO bulk single crystals
- Abstract: Publication date: 1 June 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, Volume 304
  Author(s): Chuan-Lei Jia , Tong Zhang
  We have investigated the effect of implantation and annealing temperatures on crystalline quality, disorder recovery and dopant distribution in ZnO bombarded with Er ions using Rutherford backscattering/channeling spectrometry. The channeling results indicate that the damage retains a low level in as-implanted samples due to the dynamic annealing effect during implantation at 600°C. It is also found that the implantation disorder is well recovered when the samples are annealed at 1000°C for 30min. The results also demonstrate that many Er ions diffuse towards the surface during the whole annealing program. In particular, Er is distributed almost randomly after annealing at 1000°C for 30min.
  
  PubDate: 2013-05-03T08:05:20Z
Beam characterization of a lab bench cold cathode ultra-soft x-ray generator
- Abstract: Publication date: Available online 25 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): N. Ounoughi , C. Mavon , A. Belafrites , J.-E. Groetz , M. Fromm
  The aim of this work is to characterize the Ultra Soft X-ray (USX, 1.5 keV, Al K α ) photon beam of a customized lab bench cold cathode generator. Within this generator, the electron beam is slowed down in a thin aluminium foil (16 μ m) supported by an easily exchangeable anode. It is shown that the thickness of the foil and the anode configuration determine the spatial distribution and the fluence rate of the photon beam, whereas accelerating voltage determines both fluence rate and energy spectrum feature. It is shown also that under specific operation parameters (i.e. accelerating voltage), a Gaussian energy distribution of the beam can be generated which is centred on the energy of the Al K α line (1.5 keV). Dosimetric films of GAFCHROMIC® HD-810 were used to estimate the photon fluence rate distribution of the beam. Its variation, when the generator acts as a monoenergetic source, was characterized with the two different configurations of the anode assembly. Finally, it is verified that the anode assembly consisting in a flat washer, on which the aluminium foil is set, acts as a simple point-source.
  
  PubDate: 2013-04-29T08:06:59Z
Modifications induced in the structural and optical properties of bismuth sodium borosilicate glass thin films by 120 MeV Ag7+ ions
- Abstract: Publication date: Available online 28 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Ravneet Kaur , Surinder Singh , O.P. Pandey
  Glass of the composition Bi2O3 (20%)–Na2O (15%)-B2O3 (50%)-SiO2 (15%) was prepared by conventional melt quench method. To study the effect of heavy ion irradiation on the glass network and structural units, thin films of the glass have been prepared by electron beam gun evaporation. The prepared films are irradiated using 120 MeV Ag7+ ions in the fluence range of 1×1012 to 3×1013 ions cm-2. The optical and structural properties were investigated using UV-visible absorption spectroscopy and Fourier Transform Infrared (FTIR) spectroscopic techniques. A significant decrease in the band gap is observed after irradiation which is indicative of the fact that radiation has caused compaction in the glass structure.
  
  PubDate: 2013-04-29T08:06:59Z
Characteristic of the carbon-tungsten co-deposition layers prepared by RF magnetron sputtering in a D2/Ar plasma
- Abstract: Publication date: Available online 27 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): X.H. Tang , W.Z. Zhang , L.Q. Shi , Q. Qi , B. Zhang , W.Y. Zhang , K. Wang , J.S. Hu
  A C-W co-deposition layer, formed by radio frequency magnetron sputtering, was investigated to identify the characteristics of C-W mixed layers in fusion experimental reactors. The layers were characterized by ion beam analysis, Raman spectroscopy, X-ray diffraction and scanning electron microscopy. It was found that D atoms in C-W layers were mainly trapped by the C atoms. The ratio of C/W and D concentrations in the C-W layers deposited at a pressure of 5.0 Pa and a fixed flow rate ratio were 54/31 and 5% respectively. They all increased significantly with increased flow rate of D2 but decreased with temperature at a relatively low level. The pressure dependence of the D concentration showed a maximum value around 5 Pa and it decreased with rising or decreasing pressure. Both Raman and X-ray analysis revealed that the structure of the C-W layers became more graphite-like with increasing temperature. Moreover, deuterium introduction made the tungsten carbide phase disappear in the deuterated C-W layers. Only erosion caves on the surface of the sample prepared at 300K were observed by SEM. When the temperature increased, they disappeared, and convex bodies appeared.
  
  PubDate: 2013-04-29T08:06:59Z
Study of radiation damage in InGaN and AlGaN films induced by 8.9 MeV Bi33+ ions
- Abstract: Publication date: Available online 22 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): L.M. Zhang , C.X. Li , J.T. Zhao , K.J. Yang , G.F. Zhang , T.S. Wang , C.H. Zhang
  Homogeneous radiation damage was induced in ∼250-nm-thick In0.18Ga0.82N and Al0.2Ga0.8N films by irradiation with 8.9 MeV Bi33+ ions at room temperature. The ion fluence was in the range from 5×1011 to 5×1013 cm-2. From the Rutherford backscattering/channeling (RBS/C) measurements, it is shown that Al0.2Ga0.8N had a radiation resistance at least one order of magnitude higher than In0.18Ga0.82N. When the ion fluence was increased from 1×1013 to 5×1013 cm-2, enhanced surface peaks were observed in the RBS/C spectra for both the In0.18Ga0.82N and Al0.2Ga0.8N films, which may be attributed to the high charge state of the incident ions. Moreover, from the Raman spectra measurements, the evolution of the disorder-related B1 bands and TO-like peaks with the fluence was observed for the In0.18Ga0.82N and Al0.2Ga0.8N films, respectively.
  
  PubDate: 2013-04-25T08:08:02Z
Synthesis of graphene by MEVVA source ion implantation
- Abstract: Publication date: Available online 22 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): J.J. Ying , X.H. Xiao , Z.G. Dai , W. Wu , W.Q. Li , F. Mei , G.X. Cai , F. Ren , C.Z. Jiang
  Ion implantation provides a new synthesis route for graphene, and few-layered graphene synthesis by ion implantation has been reported. Here we show the synthesis of a single layer of high-quality graphene by Metal Vapor Vacuum Arc (MEVVA) source ion implantation. Polycrystalline nickel and copper thin films are implanted with MEVVA source carbon ions at 40 kV, followed by high-temperature thermal annealing and quenching. A Raman spectrum is applied to probe the quality and thickness of the prepared graphene. A single layer of high-quality graphene is grown on the nickel films, but not on the copper films. The growth mechanisms on the nickel and copper films are explained. MEVVA source ion implantation has been widely applied in industrial applications, demonstrating that this synthesis method can be generalized for industrial production.
  
  PubDate: 2013-04-25T08:08:02Z
Influence of γ-irradiation on the optical properties of AgSbSe2 thin films
- Abstract: Publication date: Available online 22 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): A.M. Abdul-Kader , Y.A. El-Gendy
  Amorphous AgSbSe2 thin films were deposited onto glass substrates using electron beam evaporation. The effect of γ-irradiation on the optical properties of the deposited AgSbSe2 films was studied in the wavelength range 550-2500 nm. A red shift in the transmission spectra was observed with increasing γ-irradiation dose. The refractive index of the deposited films was determined as a function of γ-dose. It was established that exposure of the deposited films to γ-radiation leads to increased refractive index in the whole spectral region. The refractive index dispersion of the deposited films is adequately described by the single oscillator model, whereby, the values of the oscillator parameters were determined as a function of γ-dose. Analysis of the optical absorption coefficient revealed the presence of an indirect optical transition with band gap value decreases with increasing γ-dose.
  
  PubDate: 2013-04-25T08:08:02Z
Vibronic photoexcitation spectra of irradiated spinel MgO· nAl2O3(n=2) at low temperatures
- Abstract: Publication date: Available online 25 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Abu Zayed Mohammad Saliqur Rahman , Xingzhong Cao , Long Wei , Baoyi Wang , Ye Tao , Qiu Xu , Kozo Atobe
  A vibronic photoexcitation band at approximately 230 nm was found at 13 K in reactor neutron- and electron-irradiated magnesium aluminate spinel (MgO · nAl2O3). Vibronic structure was found to be temperature dependent and became obscure at over 120 K. Huang Rhys factor S and Debye Temperature Θ D were estimated from the temperature dependence of the 230 nm band by curve-fitting method using Debye approximation. Origin of the vibronic photoexcitation band was suggested as F center.
  
  PubDate: 2013-04-25T08:08:02Z
Light Element Quantification by Lithium Elastic Scattering
- Abstract: Publication date: Available online 23 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): F.E. Portillo , J.A. Liendo , A.C. González , D.D. Caussyn , N.R. Fletcher , O.A. Momotyuk , B.T. Roeder , I. Wiedenhoever , K.W. Kemper , P. Barber , L. Sajo-Bohus
  Accurate differential cross sections have been measured at specific beam energies and angles to be used in a method proposed previously for the simultaneous quantification of light elements ( Z < 11 ) present in evaporated liquid biological samples. Targets containing 1H, 7)Li, 12C, 16O, 19F,28Si and 197Au have been bombarded with 13 MeV 6Li3+ and 20 MeV 16O5+ beams. The 16O+1H, 16O+12C, 16O+16O, 16O+19F, 16O+28Si and 16O+197Au cross sections, shown to be consistent with the Rutherford formula predictions at 15° and 20°, have been used to determine cross sections for the 6Li+1H, 6Li+12C, 6Li+16O, 6Li+19F, 6Li+28Si and 6Li+197Au scatterings respectively at 17.5°, 24°, 25°, 26°, 28° and 30°. Although 6Li+7)Li cross sections have not been obtained from 16O+7)Li cross sections, they have been determined from measured 6Li+19F cross sections and, in addition, used to obtain 16O+7)Li cross sections at 15° and 20°. The reliability of the new cross sections determined in this investigation for the 6Li+1H, 6Li+7)Li and 6Li+19F scatterings is based on the Rutherford behavior of the measured 6Li+197Au scattering data as expected and the consistency observed between the 6Li+12C, 6Li+16O and 6Li+28Si cross sections obtained in this work and previously reported values. This research has important implications in applied physics.
  
  PubDate: 2013-04-25T08:08:02Z
Characterization of PuBe neutron sources by calorimetry and neutron assay
- Abstract: Publication date: Available online 24 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Janos Bagi , Bent Pedersen , Hamid Tagziria , László Lakosi , Cong Tam Nguyen
  In order to support and refine in-field NDA methods developed for the assay of PuBe sources the heat power of a set of such sources is measured by a heat-flow calorimeter. The Pu isotopic composition of the sources was determined by gamma spectrometry. By combining these two measurements the Pu mass of the sources was determined. In addition, the actual neutron output of the sources was also measured using a calibrated neutron coincidence counter. The measurement campaign resulted in a set of well-characterized PuBe sources, which can be used as secondary standard calibration sources.
  
  PubDate: 2013-04-25T08:08:02Z
Relationship between plant growth and cytological effect in root apical meristem after exposure of wheat dry seeds to carbon ion beams
- Abstract: Publication date: Available online 24 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Qingfang Liu , Zhuanzi Wang , Libin Zhou , Ying Qu , Dong Lu , Lixia Yu , Yan Du , Wenjie Jin , Wenjian Li
  In order to analyze the relationship between plant growth and cytological effects, wheat dry seeds were exposed to various doses of 12C6+ beams and the biological endpoints reflecting plant growth and root apical meristem (RAM) activities were investigated. The results showed that most of the seeds were able to germinate normally within all dose range, while the plant survival rate descended at higher doses. The seedling growth including root length and seedling height also decreased significantly at higher doses. Mitotic index (MI) in RAM had no changes at 10 Gy and 20 Gy and decreased obviously at higher doses, and the proportion of prophase cells had the same trend with MI. These data suggested that RAM cells experienced cell cycle arrest, which should be responsible for the inhibition of root growth after exposure to higher doses irradiation. Moreover, various types of chromosome aberrations (CAs) were observed in the mitotic cells. The frequencies of mitotic cells with lagging chromosomes and these with anaphase bridges peaked around 60 Gy, while the frequency of these with fragments increased as the irradiation doses increased up to 200 Gy. The total frequencies of mitotic cells with CAs induced by irradiation increased significantly with the increasing doses. The serious damage of mitotic chromosomes maybe caused cell cycle arrest or cell death. These findings suggested that the influences of 12C6+ beams irradiation on plant growth were related to the alternation of mitotic activities and the chromosomal damages in RAM.
  
  PubDate: 2013-04-25T08:08:02Z
The progress of X-ray fluorescence computed tomography at SSRF
- Abstract: Publication date: Available online 20 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): Biao Deng , Qun Yang , Guohao Du , Yajun Tong , Honglan Xie , Tiqiao Xiao
  X-ray fluorescence computed tomography is a stimulated emission tomography that allows nondestructive reconstruction of elements distribution in the sample and has been applied in many fields. Since 2007 we have developed X-Ray fluorescence tomography for microanalysis. In 2010, the system was established at the Shanghai Synchrotron Radiation Facility (SSRF) and preliminary experimental results were obtained at the X-ray imaging (BL13W1) and hard X-ray micro-focusing beamline (BL15U1). Recently, an ordered-subsets expectation maximization algorithm has been introduced to speed up the data acquisition process. We are now studying accelerating X-ray fluorescence computed tomography based fast scanning and the new algorithm.
  
  PubDate: 2013-04-21T08:05:26Z
Effects of X-ray irradiation on the structure and field electron emission properties of vertically aligned few-layer graphene
- Abstract: Publication date: Available online 20 April 2013
  Source:Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
  Author(s): J.Q. Wu , Y. Zhang , B. Wang , F.T. Yi , S.Z. Deng , N.S. Xu , Jun Chen
  Vertically aligned few-layer graphene is prepared using microwave plasma enhanced chemical vapor deposition. The vertically aligned few-layer graphene is irradiated by X-ray of different doses from synchrotron radiation. The main structure of vertically aligned few-layer graphene is found to remain unchanged after X-ray irradiation both in high and low vacuum. X-ray photoelectron spectroscopy results reveal that the oxygen content in pristine and irradiated few-layer graphene remain unchanged after X-ray irradiation in high vacuum. When irradiated in low vacuum, the oxygen content in few-layer graphene increases with X-ray dose. For the vertically aligned few-layer graphene irradiated in low vacuum, the work function first increases and then slightly decreases with further increase irradiation dose from 9.0×1014 phs/cm2 to 3.6×1015 phs/cm2. The field electron emission turn-on field is observed to increase from 4.0 to 9.1 MV/m after X-ray irradiation with the dose of 3.6×1015 phs/cm2. The mechanism of the changes in work function and field emission performance of vertically aligned few-layer graphene after X-ray irradiation in low vacuum are discussed.
  
  PubDate: 2013-04-21T08:05:26Z