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Intense laser–plasma interactions produce high brightness beams of gamma rays, neutrons and ions and have the potential to deliver accelerating gradients more than 1000 times higher than conventional accelerator technology, and on a tabletop scale. This paper demonstrates one of the exciting applications of this technology, namely for transmutation studies of long-lived radioactive waste. We report the laser-driven photo-transmutation of long-lived 129 I with a half-life of 15.7 million years to 128 I with a half-life of 25 min. In addition, an integrated cross-section of 97±40 mbarns for the reaction 129 I(γ ,n) 128 I is determined from the measured ratio of the (γ ,n) induced 128 I and 126 I activities. The potential for affordable, easy to shield, tabletop laser technology for nuclear transmutation studies is highlighted.

A mathematical simulation approach based on the general purpose Monte Carlo N-particle transport code MCNP was developed to predict the response of the XRF branch of the hybrid K-edge/K-XRF densitometer (HKED). The respective MCNP models for two different versions of HKED instruments currently in use were set up and experimentally validated. The setting up of the models involved comprehensive simulations of a bremsstrahlung photon source, the examination of different particle transport models, as well as the examination of different photon attenuation and X-ray fluorescence data libraries. The computation speed was significantly increased through the extensive use of the variance reduction techniques. The models were validated through the series of benchmarking experiments performed with a representative set of uranium, plutonium and mixed U/Pu reference solutions. The models and simulation approach developed are intended for: (i) establishing a consistent mathematical calibration approach for the XRF branch of the HKED instruments, which will require minimum calibration effort and time, (ii) extending the applicability of the HKED method to non-standard samples (e.g. U/Pu mixtures with unusual element ratios) and non-standard sample matrices (e.g. HM matrices from the pyro-processing of irradiated nuclear fuel) without investing a great deal of extra calibration work, and (iii) improving the accuracy of the measurements through the modelling of special measurement effects (e.g. the secondary excitation effect, the interference with X-ray escape peaks, the inconsistent unfolding of the overlapping peaks and peak background delineation in the measured XRF spectrum), which are difficult or sometimes impossible to account for experimentally.

In the last decade or so, an evolution in experimental relativistic laser-plasma physics has led to highly sophisticated lasers which are now capable of generating ultra-short pulses and can be focused to intensities in excess of 1021 W cm-2. The laser interaction with solid or gas targets can generate collimated beams of highly energetic electrons, protons and ions. These high-intensity laser systems, therefore, turn out to be versatile and powerful sources of radiation and high-energy particles, without recourse to large-scale facilities such as nuclear reactors or particle accelerators. The potential to induce various kinds of nuclear reactions with laser-induced radiation fields has been demonstrated at several laboratories in recent years. The present paper lays out a comprehensive overview of nuclear reactions induced by high-intensity laser matter interactions. Mechanisms for electron, proton and ion acceleration, in addition to secondary bremsstrahlung, positron and neutron production, are addressed, with a focus on the types of nuclear reactions that are possible and potential applications. Discussion of the extrapolation of these processes and applications to the next generation of table-top lasers under construction is also presented.

tau-Ag{sub 1/2}Cu{sub 1/2}V{sub 2}O{sub 5} compound crystallises in the monoclinic system space group C2/m with cell parameters a=11.757(4) A, b=3.6942(5) A, c=9.463(2) A, and beta=114.62(2){sup o}. The structure is build up with V{sub 4}O{sub 10} D4 double layer. The silver and copper ions are located in two different oxygenated tunnels. Examination of electronic density maps shows that while the silver ions are located in defined crystallographic sites, the copper ones are fully delocalised over the whole tunnel. Comparison with delta-Ag{sub x}V{sub 2}O{sub 5} and epsilon-Cu{sub x}V{sub 2}O{sub 5} refined structure allows to define crystal chemistry parameters governing the ionic delocalisation and give clues to predict from structural consideration the expected electrical behaviour with the aim to make possible a structural design to enhance guest species reactivity. - Graphical abstract: The role of nature and amount of guest species on their respective localisation Evidence for full delocalisation of copper ions and diffusion pathways visualisation Display Omitted

International audience; Hole-doped Ca 3 Co 4 O 9 (Co349) ceramics were prepared using solid-state reaction. Two processing strategies have been used to produce the thermoelectric oxide ceramics, Conventional and Spark Plasma (SPS) Sintering to control the grains consolidation, texturation and sample densification. Thermoelectric properties were measured and the influence of the processing conditions on the properties was evidenced. SPS favours shorter elaboration times and produces samples with larger thermoelectric properties due to better densification and alignment. The effect of the free deformation and texturation using the SPS technique is discussed. Seebeck coefficient values of 180 μV/K at 873 K are obtained.

The β--decay of 147Cs to 147Ba has been studied by means of γ- and X-ray spectroscopy. A new level scheme of 147Ba is significantly modified and extended in comparison to the one previously reported. The Advanced Time-Delayed βγγ(t) method has been applied to measure half-lives of the 46.2 and 85.4 keV levels in 147Ba yielding T 1/2 of 510(80) ps and 370(100) ps, respectively. The lifetime results combined with the deduced internal conversion coefficients allowed to assign M1 multipolarity to three γ transitions. The B(M1) values obtained for the 39.2, 46.2 and 85.4 keV transitions range from 0.017 to 0.043 W.u. and represent typical B(M1) strength in the Ba-Er region. Model calculations using a shell correction approach with the axially deformed Woods-Saxon potential predict for 147Ba an octupole deformed ground state with β3 = 0.11.

A relativistic electron beam, generated by relativistic self-focusing of an ultra-high-intensity laser pulse in a He gas jet, was targeted onto high-Z materials for conversion to high-energy bremsstrahlung. Nuclear reactions in the primary converter materials as well as in secondary and tertiary targets placed directly behind the converter were analyzed with time-resolved γ-spectroscopy. The electron-jet temperature of more than 35 MeV, matching the giant dipole resonances of heavy nuclei, enabled us to efficiently generate photo-induced nuclear reactions. The measured temperatures are significantly higher than suggested by ponderomotive scaling. We supplemented our earlier measurement of the (γ, n) reaction cross section of 129I with a method solely based on nuclear reactions. The photo-induced transmutation yields were increased by two orders of magnitude compared to earlier experiments. Simulations with the Monte Carlo code MCNPX confirm the experimental results .

Tabletop Ti : sapphire lasers, such as the Jena multi-Terawatt laser, can nowadays reach focused intensities of up to 1020 W cm−2. The interaction of this intense light field with a solid target—in our case tantalum—leads to the production of energetic bremsstrahlung x-rays. These are used to induce (γ,n)- and (γ,f)-reactions in 181Ta, 129I, 232Th, 238U and 9Be. The results are discussed in the context of laser plasma diagnostics and photo transmutation studies on radioactive material.We also report on fusion experiments in low-Z targets where the fusion neutrons are utilized to characterize ion acceleration processes.

We report the first successful laser-induced transmutation of 129I, one of the key radionuclides in the nuclear fuel cycle. 129I with a half-life of 15.7 million years is transmuted into 128I with a half-life of 25 min through a (γ, n) reaction using laser-generated Bremsstrahlung. The integral cross-section value for the (γ, n) reaction is determined. These experiments offer a new approach to studying transmutation reactions with neutral and charged particles without resource to nuclear reactors or particle accelerators.

We report the first laser induced fission of actinide nuclei with high intensity tabletop lasers. The results are discussed in the context of laser plasma diagnostics and nuclear waste handling.

One can design a critical system with fissile material in the form of a thin layer on the inner surface of a cylindrical neutron moderator such as graphite or beryllium. Recently, we have investigated the properties of critical and near critical systems based on the use of thin actinide layers of uranium, plutonium and americium. The thickness of the required fissile layer depends on the type of fissile material, its concentration in the layer and on the geometrical arrangement, but is typically in the μm–mm range. The resulting total mass of fissile material can be as low as 100 g. Thin fissile layers have a variety of applications in nuclear technology—for example in the design neutron amplifiers for medical applications and “fast” islands in thermal reactors for waste incineration. In the present paper, we investigate the properties of a neutron booster unit for spallation sources and isotope production. In those applications a layer of fissile material surrounds the spallation source. Such a module could be developed for spallation targets foreseen in the MYRRHA (L. Van Den Durpel, H. Ait Abderrahim, P. D’hondt, G. Minsart, J.L. Bellefontaine, S. Bodart, B. Ponsard, F. Vermeersch, W. Wacquier. A prototype accelerator driven system in Belgium: the Myrrha project, Technical Committee Meeting on Feasibility and Motivation for Hybrid concepts for Nuclear Energy generation and Transmutation, Madrid, Spain, September 17–19, 1997 [1]). or MEGAPIE (M. Salvatores, G.S. Bauer, G. Heusener. The MEGAPIE initiative: executive outline and status as per November 1999, MPO-1-GB-6/0_GB, 1999 [2]) projects. With a neutron multiplication factor of the booster unit in the range 10–20 (i.e. with a k eff of 0.9–0.95), considerably less powerful accelerators would be required to obtain the desired neutron flux. Instead of the powerful accelerators with proton energies of 1 GeV and currents of 10 mA foreseen for accelerator driven systems, similar neutron fluxes can be obtained with a medical cyclotron with proton energies of 350 MeV and currents of 2 mA. A basic limitation of such booster units is of course the limited lifetime of the thin fissile layer due to burn up and fission product poisoning. Nevertheless, for initial investigations of full power ADS systems, such units would allow the generation of the full neutron flux without the use of ADS class accelerators. The properties of the neutron booster have been intensively studied through systematic investigations of the different parameters (thickness, Hohlraum, reflector, etc.) of the concept. The calculations were performed with deterministic codes solving the neutron transport equation, and those results have been partially verified with the probabilistic code MCNP (Monte Carlo N-Particle Transport Code System). Layer of pure 235 U and 242m Am fuel have been initially investigated, but non-proliferation concerns led to the use of more conventional fuel layer. A specific geometry of a booster spallation source is presented. The effects of layer-burn up and lifetime are discussed.

This paper presents structural studies on crystalline and liquid AsCl(3), performed using X-ray diffraction (XRD) and wide-angle X-ray scattering (WAXS) in the 176-250 K temperature range and at 295 K for the crystalline and liquid samples, respectively. The XRD results, collected using a single-crystal diffractometer, show that AsCl(3) crystallizes in the orthorhombic system with P2(1)2(1)2(1) space group and the unit cell parameters a = 9.475(3) A, b = 11.331(2) A, and c = 4.2964(8) A at 221 K. This structure is stable in the temperature range 176-243 K. Above the melting point, at 257 K, transition to the liquid state is observed. The WAXS data were recorded up to a maximum scattering vector K(max) = 16 A(-1) and then converted to real space by the sine Fourier transform, yielding to the reduced radial distribution function (RRDF). For a series of models, based on the crystalline AsCl(3) structure, the intensity and RRDF functions have been computed and compared with the experimental data. These simulations indicate that the model consisting of six AsCl(3) molecules, arranged along the y axis, accounts satisfactorily for the experimental observation. The results of the structure analysis in both crystalline and liquid states are discussed in relation to the influence of the As lone electron pair.

We report the electronic and vibrational properties of Na2V3O7 nanotubes and compare the response with other layered and nonlayered vanadates. The electronic structure of Na2V3O7 displays a strong similarity to that of nontubular vanadates. We assign the 1.2-eV band as a V d → d excitation and the 3.3- and 3.9-eV bands as O 2p → V 3d charge-transfer structures. Although band structure calculations predict additional fine structure in the density of states because of the tubular morphology, such features are not observed in the absorption spectrum. The vibrational spectrum displays triplet mode splitting as a result of reduced site symmetry, consistent with the three sightly different vanadium atoms that form the basic structural unit. A low-frequency rattling mode is observed in Na2V3O7 at 88 cm-1. This unique characteristic of the Na+-ion intercalated tubes might be connected with the ionic conductivity.

A comprehensive study has been carried out of the yield pattern of fission products formed in fast neutron-induced fission of 233U. The isotope separator on-line facility at Studsvik to the R2-0 nuclear reactor was used for rapid separation of the fission products. At a target temperature of 2250°C fission products of the elements from zinc (Z = 30) to barium (Z = 56) are released, with the exception of yttrium, zirconium, niobium, molybdenum, technetium, ruthenium and rhodium. The individual isotopes are then available for study, implying that an almost complete mapping of the yield distribution can be made. In the analysis, the delay between production and measurement and the overall separator efficiency for three consecutive elements (the one under study and its parent and grand parent) are taken into account. Independent and/or cumulative yields have been obtained for 203 nuclear species, among them 59 isomeric states.

This study deals with the bubbling phenomenon which appears in some drying conditions on paint films applied as thin layers on SMC substrates. The bubbles and craters origin can be due either to reactions which may occur at the interface paint / SMC either to inadequate drying conditions which affect the polymerization reaction (gelation, viscosity) and the solvent vaporization. Firstly, we reported data describing the solvent interaction with the SMC substrate - namely the contact angle, the interfacial tension, the absorption kinetics and the sorption isotherms - and the relationship between the bubbling defects and the numerous process variable (operating conditions, paint formulation and support properties). Then, we gathered experimental data concerning the influence of different parameters (state and type of substrate, temperature, heating mode, film thickness. paint formulation, etc.) on the bubbling phenomenon and we tried to establish some quantitative interpretation. It proved that this...

(M2) and (M3) VO2 high pressure phases have been obtained at 65kbars by Chamberland. Both phases crystallize in the monoclinic system, (M2) with the space group C2/m and unit cell dimensions a = 9.083A, b = 5.763A, c = 4.532A, β = 90.3 ° whereas (M3) belongs to P2/m with a = 4.506A, b = 2.899A, c = 4.617A and β = 91.79 °. Based on this data ab initio structures have been elaborated and adjusted to fit their experimental powder patterns. (M2) structure exhibits two crystallographically different infinite parallel [VO4]n4n− strings of VO6 edge shared octahedra interconnected by apices alike in the rutile structure but the oxygens are hexagonally close packed. The (M3) variety shows also two different [VO4]n4n− strings but the general network now is rutile like slightly distorted. Vanadium atoms are situated in distorted oxygen octahedra, the V O bond lengths ranging from 1.66A to 2.15A with the V4+-V4+ pairing, V1-V1 = 2.70A and V2-V2 = 2.89A in (M2). In (M3) the V O distances range from 1.75A to 2.10A and V1-V1 = V2-V2 = 2.90A. The homopolar V4+ pairs evidenced in the (M2) form and the general unsymmetrical arrangement of oxygen about V4+ are in excellent agreement with the unusual physical properties of these two high pressure varieties.

The structural change occurring in between the paraelectric and the ferroelectric phases is investigated by means of X-ray diffraction. Details of the structure in both phases are obtained and the role of the lone pair is discussed in the light of structural data. In agreement with the 2/ m to m symmetry lowering, polar displacements are found within the m plane away from a particular crystallographic direction but antiparallel displacements occur also. These results are discussed in the frame of the phenomenological theory which predicts a particular temperature dependence of the dielectric polarization in this crystal.

The VUV spectroscopic study of -particle-excited neon-krypton mixtures showed the occurrence of intense energy transfers from neon to krypton. The spectra of mixtures containing a few per cent krypton are similar to those of pure krypton. They are dominated by krypton's second continuum centred at 148 nm, its intensity increasing with the krypton concentration and the total pressure. Furthermore, a low-intensity emission due to the heteronuclear ion situated at 166.5 nm was also observed. The kinetic study of the second continuum of krypton revealed that heteronuclear reactions play an important role in the formation of at low krypton partial pressures. Their reaction constants were found to be for the state and for . Under high krypton pressures, homonuclear reactions were dominant, the reaction constant being for the state and for .

In this study the kinetics and phase changes which occurred during the convective drying of a model car paint based on the polyurethane chemistry is described. The competition between the kinetics of the solvent removal and the phase changes, such as the gelation and/or the vitrification of the polyurethane, needs to be taken into account to avoid the defects in the resulting dried coating. The kinetics of polycondensation of a two-component polyurethane based on polyester triol and triisocyanate in a mixture of various solvents was studied as a 100 µm thick layer on sheet molding compound (SMC) and zinc plated steel plates. Differential scanning calorimetry (DSC) and Fourier-Transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA) during isothermal curings allowed us to determine the rate constants and the activation energies by using second and third order autocatalytic models.

Measurements are made for variations of the effective secondary emission coefficient γ with reduced field E/p. Plane-parallel copper electrodes (5 cm diameter) are sustained with a dc voltage (0

Single crystals of diantimony molybdenum hexaoxide have been grown by solid-state reaction. This oxide crystallizes as a layered structure, as in the case of the previously reported Sb 2 WO 6 . Mo atoms are located in severely distorted O-atom octahedra while each Sb atom is bonded to five O atoms, three at short distances and two at longer distances, retaining the three-dimensional array.

Cet article presente une synthese des travaux d'un groupe de laboratoires qui, sous l'egide de la DRET, a pendant cinq ans conduit des etudes visant a eclaircir differents aspects de la physico-chimie de resines thermodurcissables a base d'arylcyanates. Les resultats obtenus sur les structures de reseaux ont ete correles avec le comportement et les proprietes d'usage des materiaux, et en particulier pour les composites structuraux destines a des applications dans l'industrie aerospatiale qui en derivent. En ce qui concerne la polymerisation des resines cyanate pures, un des principaux resultats des recherches menees a ete la mise en evidence d'une sensibilite non negligeable a l'environnement, en particulier a l'eau, susceptible de provoquer des modifications de la reactivite des monomeres ou des oligomeres, conduisant a des imperfections de la structure du reseau entrainant des modifications des caracteristiques du polymere reticule (transitions vitreuse et sous-vitreuse, reprise d'eau, proprietes mecaniques). L'addition de prepolymeres epoxy, qui apporte des avantages au niveau de la mise en oeuvre et surtout du prix, se traduit egalement par une forte complication des mecanismes de reticulation et, partant, des structures de reseau obtenues rendant leur controle plus difficile sans que ne se degagent des ameliorations de performances evidentes. L'utilisation d'additifs elastomeres ou thermoplastiques entraine des modifications de comportement, dont il a ete possible de degager un certain nombre de traits caracteristiques, tant du point de vue des regles de melange et du controle des morphologies de systemes biphasiques obtenus, que des ameliorations de performances qu'on peut en attendre.

Le but de ce travail est de decrire et analyser le comportement viscoelastique et les proprietes a rupture de reseaux thermodurcissables epoxy/amine en liaison avec la structure. Deux parametres essentiels sont etudies : la flexibilite des chaines et la densite de reticulation dans une meme serie structurale de reseaux modeles.

The light pulses of two emissions of the molecule XeCl, centered at 308 and 345 nm, both have decay time constants that behave in a very similar way with respect to variations in the partial pressures of xenon and HCl; this is explained by collisional coupling between the states B and C of XeCl which are at the origin of the two emissions. The identification of the different collision processes and the determination of the reaction rate constants particularly underline the occurrence of a three‐body collision process between XeCl (B,C), Xe, and HCl; the rate constant is kM=(5.85±2.70)×10−5 Torr−2 ns−1. Measurements were also made of the coupling constants B→C and C→B which were found to be kBC=(2.56±1.05)×10−4 Torr−1 ns−1 and kCB=(1.45±1.05)×10−4 Torr−1 ns−1. The deduced energy gap between the two states (EB−EC=119 cm−1) is in very good agreement with the values in the literature.

Measurements of ion-induced nuclear reactions have been used to diagnose ion acceleration from the interaction of high-intensity (>1019 W cm−2) laser light with solid targets. Nuclear activation of catcher materials surrounding the interaction region has been studied using a high-resolution germanium detector. It was found that, when a 100 μm thick Al target foil was preheated, the proton flux produced from the laser–foil interaction was considerably reduced. Observed heavy-ion-induced reactions are used with calculated reaction cross sections to quantify ion acceleration.

In the scope of providing new chemical insight of the oxidation states of copper and vanadium, crystal structures of VOB's β′-Cu x V2O5 with x = 0.29, 0.47 and 0.59, have been carefully investigated. The structures are monoclinic, space group C2/m, with a = 15.233(3) Å, 15.218(1) Å, 15.2007(7) Å, b = 3.6133(9) Å, 3.6271(6) Å, 3.6375(3) Å, c = 10.0927(9) Å, 10.087(8) Å, 10.0925(4) Å, β = 107.30(1) Å, 106.55(4) Å, 106.13(2)°, R = 0.0467, 0.0290, 0.0315. A thorough examination of bond distances and angles allows to give a precise description of the structural evolution versus increasing values of copper insertion x in the tunnels of the [V2O5] n framework. The three independent vanadium atoms exhibit distorted oxygen coordination polyhedra, octahedra for V(1) and V(2), square pyramid for V(3). The copper, as revealed by successive Fourier map differences, is spreaded over a sort of toroidal section inserted in a huge oxygen trigonal bipyramid; more precisely the copper coordination changes, in its asymmetric site, from CN4 for Cu(1) (in the mirror plane) to CN3 for Cu(2) (apart the mirror plane, Δy ∼± 0.12) which rarely occurs in sulphides but, up to now never in oxides. The multiplication of Cu sites as well as their various coordination let us think that copper oxidation states could be not unique; such hypothesis is confirmed by ESCA measurements, which clearly indicate that simultaneously Cu(I) and Cu(II) are present. Such results establish that β′′-CuxV2O5 phases are doubly mixed valence vanadium oxide bronzes and can be formally written: Cu xt +Cu x(1−t) 2+V2−x(2−t) 5+V x(2−t) 4+O5 (t stands for Cu(I) rate).

A laboratory spectrometer designed for routine extended x‐ray absorption fine structure (EXAFS) measurements in dispersive mode is described. Factors determining energy range and resolution are detailed. An empirical energy calibration procedure is proposed. EXAFS spectra obtained for copper and zirconium metal foil and molecular complex ZrOCl2 compare favorably with data obtained using a conventional synchrotron facility.

The thermal decomposition of sodium oxalate in the presence of vanadium pentoxide in 1:2 molar ratio affords the vanadium bronze α'-NaV 2 O 5 . Complementary techniques such as thermogravimetry (TG), differential thermal analysis (DTA), gas analysis (GC), X-ray powder diffraction (XRD) and infrared spectroscopy (IR) were applied to provide information on the operative mechanism. A promotive effect of vanadium pentoxide on the decomposition of sodium oxalate takes place. Carbonate species and carbon monoxide could not be detected as intermediates during the decomposition which occurs over a wide range of temperatures, typically between 200 and 525°C. The progressive formation of Na x V 2 O 5 bronzes with x increasing up to unity with temperature leads us to propose that the carbon-carbon bond cleavage of the oxalate is promoted by electron transfer between the oxalate anion and the vanadium pentoxide matrix. Such behaviour is dependent on the redox potential of the metal ion initially present in the oxalate and of vanadium pentoxide.

In two-component Xe/HCl mixtures irradiated with alpha -particles, emissions centred at 308, 345 and 470 nm are observed; they correspond to the (B to X) and (C to A) transitions of XeCl* and to the transition (42 Gamma to 12 Gamma ) of Xe2Cl*, respectively. The Xe2Cl* emission was only seen when HCl was present as traces and Xe was at a pressure of over 200 Torr. The experiments showed the simultaneous presence of the emissions of the third continuum of xenon (290 and 390 mm) which compete with those of XeCl*. This implies that the Xe2+* ions and their precursors, which participate in the reactions of XeCl (B, C) formation are also at the origin of the third continuum. By means of intensity measurements, the energy gap between states B and C of XeCl was estimated at 118+or-40 cm-1.

For pt.I see ibid., vol.25, no.23, p.5141-8 (1992). In Ne-Xe mixtures molecular states responsible for the second continuum of xenon ( lambda =170 nm) are shown to be created by homonuclear and heteronuclear reactions from the 3P1 and 3P2 states of xenon. In Ar-Xe mixtures, at lambda =826 nm, two lines of argon and xenon are superimposed; it is observed that the atomic states responsible for the two transitions undergo decay (for argon) or creation (for xenon). The creation of the 2p10 xenon state is measured from the transition at lambda =980 nm which it produces. In the Ne-Xe mixture, at lambda =882 nm, it is the decay, through homonuclear and heteronuclear mechanisms, of the precursor 2p8 state of xenon which is demonstrated. In each case, the rate constants of the corresponding reactions are reported.

The thermal decomposition of sodium oxalate in the presence of vanadium pentoxide in 1:2 molar ratio affords the vanadium bronze α'-NaV 2 O 5 . Complementary techniques such as thermogravimetry (TG), differential thermal analysis (DTA), gas analysis (GC), X-ray powder diffraction (XRD) and infrared spectroscopy (IR) were applied to provide information on the operative mechanism. A promotive effect of vanadium pentoxide on the decomposition of sodium oxalate takes place. Carbonate species and carbon monoxide could not be detected as intermediates during the decomposition which occurs over a wide range of temperatures, typically between 200 and 525°C. The progressive formation of Na x V 2 O 5 bronzes with x increasing up to unity with temperature leads us to propose that the carbon-carbon bond cleavage of the oxalate is promoted by electron transfer between the oxalate anion and the vanadium pentoxide matrix. Such behaviour is dependent on the redox potential of the metal ion initially present in the oxalate and of vanadium pentoxide.

Nuclear Security aims at the prevention and detection of and response to, theft, sabotage, unauthorized access, illegal transfer or other malicious acts involving nuclear material". Nuclear Forensics is a key element of nuclear security. Nuclear Forensics is defined as a methodology that aims at re-establishing the history of nuclear material of unknown origin. It is based on indicators that arise from known relationships between material characteristics and process history. Thus, nuclear forensics analysis includes the characterization of the material and correlation with production history. To this end, we can make use of parameters such as the isotopic composition of the nuclear material and accompanying elements, chemical impurities, macroscopic appearance and microstructure of the material. In the present paper, we discuss the opportunities for attribution of nuclear material offered by nuclear forensics as well as its limitations. Particular attention will be given to the role of nuclear reactions. Such reactions include the radioactive decay of the nuclear material, but also reactions with neutrons. When uranium (of natural composition) is exposed to neutrons, plutonium is formed, as well as 236U. We will illustrate the methodology using the example of a piece of uranium metal that dates back to the German nuclear program in the 1940's. A combination of different analytical techniques and model calculations enables a nuclear forensics interpretation, thus correlating the material characteristics with the production history., JRC.E.8-Nuclear Safeguards and Forensics

(M2) and (M3) VO2 high pressure phases have been obtained at 65kbars by Chamberland. Both phases crystallize in the monoclinic system, (M2) with the space group C2/m and unit cell dimensions a = 9.083A, b = 5.763A, c = 4.532A, β = 90.3 ° whereas (M3) belongs to P2/m with a = 4.506A, b = 2.899A, c = 4.617A and β = 91.79 °. Based on this data ab initio structures have been elaborated and adjusted to fit their experimental powder patterns. (M2) structure exhibits two crystallographically different infinite parallel [VO4]n4n− strings of VO6 edge shared octahedra interconnected by apices alike in the rutile structure but the oxygens are hexagonally close packed. The (M3) variety shows also two different [VO4]n4n− strings but the general network now is rutile like slightly distorted. Vanadium atoms are situated in distorted oxygen octahedra, the V O bond lengths ranging from 1.66A to 2.15A with the V4+-V4+ pairing, V1-V1 = 2.70A and V2-V2 = 2.89A in (M2). In (M3) the V O distances range from 1.75A to 2.10A and V1-V1 = V2-V2 = 2.90A. The homopolar V4+ pairs evidenced in the (M2) form and the general unsymmetrical arrangement of oxygen about V4+ are in excellent agreement with the unusual physical properties of these two high pressure varieties.

In a recent experiment [1] a high efficiency regime of stable electron acceleration to kinetic energies ranging from 10 to 40 MeV has been achieved. The main parameters of the electron bunches are comparable with those of bunches provided by commercial Radio‐Frequency based Linacs currently used in Hospitals for Intra‐Operative Radiation Therapy (IORT). IORT is an emerging technique applied in operating theaters during the surgical treatment of tumors. Performances and structure of a potential laser‐driven Hospital accelerator are compared in detail with the ones of several commercial devices. A number of possible advantages of the laser based technique are also discussed.

High-energy electrons can be produced in interactions of intense, ultra-short laser pulses with plasmas. Experiments conducted in the regime of moderate laser power (a few terawatts [TW]) are attracting increasing attention for their possibility of optimizing the acceleration process. Here we report the successful production of several-MeV electron bunches in interactions of femtosecond laser pulses from a 10 TW tabletop laser with supersonic gas-jets. The laser–plasma interaction and the obtained electron bunches have been characterized in detail, and conditions for stable and reproducible acceleration have been found. The accelerated electron bunches have been characterized by means of the measurement of the induced photo-activation of a gold sample via bremsstrahlung-generation of photons with suitable energy. The obtained result opens up a wide range of possible applications of the compact electron source for the concerns of nuclear physics studies. Some of them are briefly considered in this paper.

At wavelengths lower than 550 nm, addition of argon or neon to xenon gives rise to the emission of continua produced by heteronuclear processes (ArXe, Ne+Xe and NeXe+) indicating large energy transfers from the preponderant and lighter gas. Above 550 nm the transitions observed were all produced by atomic processes. Addition of argon to xenon causes an enhancement of certain xenon emissions ( lambda =770 nm in particular): this does not occur in Ne-Xe mixtures. These processes involve, above all, high energy states of xenon (configuration 5d). The kinetic study of certain emissions is dealt with in paper II (Galy et al., 1993).

NUCLEONICA is a new nuclear science web portal from the European Commission's Joint Research Centre. The portal provides a customisable, integrated environment and collaboration platform for the nuclear sciences using the latest internet "Web 2.0" dynamic technology. NUCLEONICA is aimed at professionals, academics and students working with radionuclides in fields as diverse as the life sciences (e.g., biology, medicine, agriculture), the earth sciences (geology, meteorology, environmental science) and the more traditional disciplines such as nuclear power, health physics and radiation protection, nuclear and radio-chemistry, and astrophysics. It is also used as a knowledge management tool to preserve nuclear knowledge built up over many decades by creating modern web-based versions of so-called legacy computer codes., JRC.E.4-Nuclear fuels

At low pressures, excitation is due to the absorption of three photons and causes emission of the resonance line and the related first continuum ( lambda approximately 125 nm). At higher pressures, excitation mainly arises from a photon of the third harmonic of the laser wave and the second continuum ( lambda approximately 148 nm) is detected. Luminescence attenuations in the excitation spectra can be explained by the absorption of a fourth photon. The natural lifetime of the 3P1 is determined using Holstein's theory. The role of two and three-body collisions is demonstrated in the decay of the 3P1 state as in the role of three-body collisions for the 3P2 state. The corresponding rate constants are determined and the lifetime of the 1u(3P2) state evaluated.

A gamma-ray source with an intense component around the giant dipole resonance for photonuclear absorption has been obtained via bremsstrahlung of electron bunches driven by a 10-TW tabletop laser. 3D particle-in-cell simulation proves the achievement of a nonlinear regime leading to efficient acceleration of several sequential electron bunches per each laser pulse. The rate of the gamma-ray yield in the giant dipole resonance region (8

Neutron production rates using laser-accelerated protons from high-energy single-shot laser (giant pulse laser) and low-energy high-repetition tabletop laser systems are compared. With the VULCAN giant pulse laser, more than 10 9 neutrons per shot were produced in a nanosecond pulse through (p,m) reactions with lead. In contrast, a current state-of-the-art tabletop laser theoretically can produce 10 6 to 10 7 neutrons per second in repetitional nanosecond pulses. It is estimated that next-generation tabletop lasers currently under construction will be capable of producing nanosecond neutron pulses at a rate of 10 10 neutrons per second.

Several well-known phosphors compositions based on rare earth orthoborates, with the general formula LnBO 3 with Ln = [Y 0.95− y Gd y Eu 0.05 ] or [Y 0.95− y Gd y Tb 0.05 ], and the cubic oxide (Y 0.96 Eu 0.04 ) 2 O 3 have been synthesized by spray-pyrolysis (SP) and additional thermal treatments. Samples with the unique hexagonal YBO 3 type phase have been obtained. The particles are spherical, the average diameter is around 2 μm, with a relatively narrow spreading. The borate spheres are not dense: porosities are observed, but do not exhibit the core-shell aspect observed for Y 2 O 3 :Eu 3+ spheres. The emission spectra, the relative intensities, and the transient characteristics of phosphors under VUV excitation by a pure Xe gas discharge have been measured in a specially developed experimental set-up. The integrated Eu 3+ emission intensities are at least 50% higher for SP yttrium borates than for SP yttrium oxide; the decay times τ 10 are 13 ± 1 msec and 4.6 ± 0.4 msec, respectively. Up to 80% efficiency of a commercial green phosphor (Zn 2 SiO 4 :Mn 2+ ), and τ 10 = 15 ± 1 msec were easily achieved in spray pyrolysed Tb 3+ yttrium borates. The Gd/Y substitution and the annealing temperature have a very weak effect on the europium and the terbium luminescence efficiencies and decay times.