41 resultados para SYNCHROTRON RADIATION SOURCES
Resumo:
γ-Ray sources are among the most fundamental experimental tools currently available to modern physics. As well as the obvious benefits to fundamental research, an ultra-bright source of γ-rays could form the foundation of scanning of shipping containers for special nuclear materials and provide the bases for new types of cancer therapy.
However, for these applications to prove viable, γ-ray sources must become compact and relatively cheap to manufacture. In recent years, advances in laser technology have formed the cornerstone of optical sources of high energy electrons which already have been used to generate synchrotron radiation on a compact scale. Exploiting the scattering induced by a second laser, one can further enhance the energy and number of photons produced provided the problems of synchronisation and compact γ-ray detection are solved.
Here, we report on the work that has been done in developing an all-optical and hence, compact non-linear Thomson scattering source, including the new methods of synchronisation and compact γ-ray detection. We present evidence of the generation of multi-MeV (maximum 16–18 MeV) and ultra-high brilliance (exceeding 1020 photons s−1mm−2mrad−2 0.1% BW at 15 MeV) γ-ray beams. These characteristics are appealing for the paramount practical applications mentioned above.
Resumo:
This work combines microscopy, synchrotron radiation X-ray diffraction, differential scanning calorimetry and thermodynamic calculations in the characterisation of phase transformation behaviour of a Ti–46Al–1.9Cr–3Nb alloy upon continuous heating at constant rates. It has been found that the Ti–46Al–1.9Cr–3Nb alloy after being forged at 1200 °C without further treatment has a duplex microstructure consisting of fine equiaxed and lamellar ? grains with a small amount of a2 plates and particles and about 1 wt.% B2 phase. Differential scanning calorimetry revealed reproducibly several thermal effects upon heating of the as-forged alloy. These thermal effects are related to the equilibration and homogenisation of the sample, change of phase ratios between a2, ? and B2 phases in particular the increase of B2 in respect to a2 and ?, and the following five phase transformations: a2 + ? + B2 a + ? + B2, a + ? + B2 a + ?, ? + a a, a a + ß, a + ß a + ß + L. The observation of these transformations by differential scanning calorimetry is largely in agreement with literature phase diagrams and thermodynamic calculations, though care is needed to consider the different alloy compositions. Kinetics of the ? + a a phase transformation in the Ti–46Al–1.9Cr–3Nb alloy has been quantitatively derived from the calorimetry data, giving phase compositions at any point during the transformation upon continuous heating.
Resumo:
Modern intense ultrafast pulsed lasers generate an electric field of sufficient strength to permit tunnel ionization of the valence electrons in atoms(1). This process is usually treated as a rapid succession of isolated events, in which the states of the remaining electrons are neglected(2). Such electronic interactions are predicted to be weak, the exception being recollision excitation and ionization caused by linearly polarized radiation(3). In contrast, it has recently been suggested that intense field ionization may be accompanied by a two-stage 'shake-up' reaction(4). Here we report a unique combination of experimental techniques(5-8) that allows us to accurately measure the tunnel ionization probability for argon exposed to 50-fs laser pulses. Most significantly for the current study, this measurement is independent of the optical focal geometry(7,8), equivalent to a homogenous electric field. Furthermore, circularly polarized radiation negates recollision. The present measurements indicate that tunnel ionization results in simultaneous excitation of one or more remaining electrons through shake-up(9). From an atomic physics standpoint, it may be possible to induce ionization from specific states, and will influence the development of coherent attosecond extreme-ultraviolet-radiation sources(10). Such pulses have vital scientific and economic potential in areas such as high-resolution imaging of in vivo cells and nanoscale extreme-ultraviolet lithography.
Resumo:
Polar photodissociation of CFnCl4-n (n=0-2) has been studied using synchrotron radiation within the energy range 195-217 eV. The first observations of negative photoion fragments from these molecules after core excitation are reported. In addition to observing a number of previously known resonances two additional resonant states, just above the Cl 2p ionization limit, are observed and play an important role in the polar photodissociation process. The difficulties in identifying these above threshold spin-split features using negative photoion spectroscopy are discussed.
Resumo:
Imidazo[4,5-f]-1,10-phenanthroline and pyrazino[2,3-f]-1,10-phenanthroline substituted with long alkyl chains are versatile ligands for the design of metallomesogens because of the ease of ligand substitution. Whereas the ligands and the corresponding rhenium(I) complexes were not liquid-crystalline, mesomorphism was observed for the corresponding ionic ruthenium(II) complexes with chloride, hexafluorophosphate, and bistriflimide counterions. The mesophases were identified as smectic A phases by high-temperature small-angle X-ray scattering (SAXS) using synchrotron radiation. The transition temperatures depend on the anion, the highest temperatures being observed for the chloride salts and the lowest for the bistriflimide salts. The ruthenium(II) complexes are examples of luminescent ionic liquid crystals.
Resumo:
Particle-in-cell (PIC) simulations of relativistic shocks are in principle capable of predicting the spectra of photons that are radiated incoherently by the accelerated particles. The most direct method evaluates the spectrum using the fields given by the Lienard-Wiechart potentials. However, for relativistic particles this procedure is computationally expensive. Here we present an alternative method that uses the concept of the photon formation length. The algorithm is suitable for evaluating spectra both from particles moving in a specific realization of a turbulent electromagnetic field or from trajectories given as a finite, discrete time series by a PIC simulation. The main advantage of the method is that it identifies the intrinsic spectral features and filters out those that are artifacts of the limited time resolution and finite duration of input trajectories.
Resumo:
A new efficient type of gadolinium-based theranostic agent (AGuIX®) has recently been developed for MRI-guided radiotherapy (RT). These new particles consist of a polysiloxane network surrounded by a number of gadolinium chelates, usually 10. Owing to their small size (<5 nm), AGuIX typically exhibit biodistributions that are almost ideal for diagnostic and therapeutic purposes. For example, although a significant proportion of these particles accumulate in tumours, the remainder is rapidly eliminated by the renal route. In addition, in the absence of irradiation, the nanoparticles are well tolerated even at very high dose (10 times more than the dose used for mouse treatment). AGuIX particles have been proven to act as efficient radiosensitizers in a large variety of experimental in vitro scenarios, including different radioresistant cell lines, irradiation energies and radiation sources (sensitizing enhancement ratio ranging from 1.1 to 2.5). Pre-clinical studies have also demonstrated the impact of these particles on different heterotopic and orthotopic tumours, with both intratumoural or intravenous injection routes. A significant therapeutical effect has been observed in all contexts. Furthermore, MRI monitoring was proven to efficiently aid in determining a RT protocol and assessing tumour evolution following treatment. The usual theoretical models, based on energy attenuation and macroscopic dose enhancement, cannot account for all the results that have been obtained. Only theoretical models, which take into account the Auger electron cascades that occur between the different atoms constituting the particle and the related high radical concentrations in the vicinity of the particle, provide an explanation for the complex cell damage and death observed.
Resumo:
Gold nanoparticles (GNPs), have been demonstrated as effective preclinical radiosensitising agents in a range of cell models and radiation sources. These studies have also highlighted difficulty in predicted cellular radiobiological responses mediated by GNPs, based on physical assumptions alone, and therefore suggest a significant underlying biological component of response. This study aimed to determine the role of mitochondrial function in GNP radiosensitisation. Using assays of DNA damage and mitochondrial function through levels of oxidation and loss of membrane potential, we demonstrate a potential role of mitochondria as a central biological mechanism of GNP mediated radiosensitisation.
Resumo:
High resolution synchrotron radiation core level photoemission measurements have been used to undertake a comparative study of the high temperature stability of ultrathin Al2O3 layers deposited by atomic layer deposition (ALD) on both sulphur passivated and native oxide covered InGaAs. The residual interfacial oxides between sulphur passivated InGaAs and the ultrathin Al2O3 layer can be substantially removed at high temperature (up to 700 °C) without impacting on the InGaAs stoichiometry while significant loss of indium was recorded at this temperature on the native oxide InGaAs surface.
Resumo:
We study synchrotron radiation emission from laser interaction with near critical density (NCD) plasmas at intensities of 1021 W∕cm2 using three-dimensional particle-in-cell simulations. It is found that the electron dynamics depend on the laser shaping process in NCD plasmas, and thus the angular distribution of the emitted photons changes as the laser pulse evolves in space and time. The final properties of the resulting synchrotron radiation, such as its overall energy, the critical photon energy, and the radiation angular distribution, are strongly affected by the laser polarization and plasma density. By using a 420 TW∕50 fs laser pulse at the optimal plasma density (∼1nc ), about 108 photons/0.1% bandwidth are produced at multi-MeV photon energies, providing a route to ultraintense, femtosecond gamma ray pulses.
Resumo:
The collective response of charged particles to intense fields is intrinsic to plasma accelerators and radiation sources, relativistic optics and many astrophysical phenomena. Here we show that a relativistic plasma aperture is generated in thin foils by intense laser light, resulting in the fundamental optical process of diffraction. The plasma electrons collectively respond to the resulting laser near-field diffraction pattern, producing a beam of energetic electrons with a spatial structure that can be controlled by variation of the laser pulse parameters. It is shown that static electron-beam and induced-magnetic-field structures can be made to rotate at fixed or variable angular frequencies depending on the degree of ellipticity in the laser polarization. The concept is demonstrated numerically and verified experimentally, and is an important step towards optical control of charged particle dynamics in laser-driven dense plasma sources.
Resumo:
Photoionization cross section calculations on the halogen-like ions; Kr + and Xe + have been performed for a photon energy range from each ion threshold to 15 eV, using large-scale close-coupling calculations within the Dirac--Coulomb R -matrix approximation. The results from our theoretical work are compared with recent measurements made at the ASTRID merged-beam set-up at the University of Aarhus in Denmark and from the Fourier transform ion cyclotron resonance trap method at the SOLEIL synchrotron radiation facility in Saint-Aubin, France Bizau et al (2011 J. Phys. B: At. Mol. Opt. Phys. 44 055205) and the advanced light source M{ü}ller (2012 private communication), Aguliar et al (2012 J. Phys.: Conf. Ser . at press). For each of these complex ions our theoretical cross section results over the photon energy range investigated are seen to be in excellent agreement with experiment. Resonance energy positions and quantum defects of the prominent Rydberg resonances series identified in the spectra are compared with experiment for these complex halogen-like ions.