Photon-avalanche upconversion of red light into blue light in a thulium-doped fluorozirconate fibre

We report the investigation of the photon-avalanche effect in heavily thulium-doped fluorozirconate fibre. Pumping at red wavelengths, which are not resonant with the ground-state absorption, gives blue emission at 450nm and 480nm

Blue avalanche upconversion in Tm:ZBLAN fibre

We report the investigation of the photon avalanche effect in heavily doped Tm:ZBLAN fibre at room temperature. Pumping at 630nm to 650nm, which is not resonant with the ground state absorption, gives intense blue emissions at 450nm and 480nm. The time evolution of the absorption and emission show a slow decaying oscillation before steady state is reached

Consistency checks of results from a Monte Carlo code intercomparison for emitted electron spectra and energy deposition around a single gold nanoparticle irradiated by X-rays

Organized by the European Radiation Dosimetry Group (EURADOS), a Monte Carlo code intercomparison exercise was conducted where participants simulated the emitted electron spectra and energy deposition around a single gold nanoparticle (GNP) irradiated by X-rays. In the exercise, the participants scored energy imparted in concentric spherical shells around a spherical volume filled with gold or water as well as the spectral distribution of electrons leaving the GNP. Initially, only the ratio of energy deposition with and without GNP was to be reported. During the evaluation of the exercise, however, the data for energy deposition in the presence and absence of the GNP were also requested. A GNP size of 50 nm and 100 nm diameter was considered as well as two different X-ray spectra (50 kVp and 100 kVp). This introduced a redundancy that can be used to cross-validate the internal consistency of the simulation results. In this work, evaluation of the reported results is presented in terms of integral quantities that can be benchmarked against values obtained from physical properties of the radiation spectra and materials involved. The impact of different interaction cross-section datasets and their implementation in the different Monte Carlo codes is also discussed

Palaeontological data about the climatic trends from Chattian to present along the Northeastern Atlantic frontage

Climatic changes that affected the Northeastern Atlantic frontage are analyzed on the basis of the evolution of faunas and floras from the late Oligocene onwards. The study deals with calcareous nannoplankton, marine micro- and macrofaunas, some terrestrial vertebrates and vegetal assemblages. The climate, first tropical, underwent a progressive cooling (North-South thermic gradient). Notable climatic deteriorations (withdrawal towards the South or disappearance of taxa indicative of warm climate and appearance of "cold" taxa) are evidenced mainly during the Middle Miocene and the late Pliocene. Faunas and floras of modern pattern have regained, after the Pleistocene glaciations, a new climatic ranging of a temperate type in the northern part

Photon avalanche upconversion in heavily thulium-doped ZBLAN fibre

Photon avalanche mechanism results from a cross relaxation energy transfer induced build up of population in an intermediate metastable level without resonant Ground State Absorption (GSA). From this level a resonant absorption occurs to populate a higher level The main characteristics of such process is a power threshold which corresponds to a sudden increase of the fluorescence arising from the upper excited state as well as a slowing and a change of the rise shape of the transient signals

Theoretical study of W-values for particle impact on water

The W-values and the differential values w, were calculated by electron, proton and antiproton impact on liquid and vapor water. Two different theoretical approximations were used: the Fowler Equation (based on the Continuous Slowing Down Approximation), and the Monte Carlo code MDM, which does an event-by-event tracking of all generated particles in the media. The dependence on the type and charge of the projectiles and the relevance on the appropriate inelastic cross sections employed in the calculations were studied. For electron impact, results obtained with both models are in good agreement with experimental data and with other theoretical calculations. However, the MDM results are more representative of the stochastic nature of radiation-media interactions. The w-values for swift proton and antiproton impact on vapor water, calculated using the Fowler Equation, are in very good agreement with the results obtained by electron impact in the same velocity regime.Fil: Tessaro, Veronica Belen. Universite Claude Bernard Lyon 1. Institut de Physique Nucléaire de Lyon.; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Poignant, F.. Universite Claude Bernard Lyon 1. Institut de Physique Nucléaire de Lyon.; FranciaFil: Gervais, B.. Universite de Caen Basse Normandie; FranciaFil: Beuve, M.. Universite Claude Bernard Lyon 1. Institut de Physique Nucléaire de Lyon.; FranciaFil: Galassi, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

Theoretical derivation and benchmarking of cross sections for low-energy electron transport in gold

International audienceSimulation of transport of electrons through matter is used in many applications. Some of them need models that are both efficient in terms of computing time and accurate over a wide range of electron energy. For certain applications such as radiochemistry and radiotherapy enhanced by metallic nanoparticles, it is desirable to consider relatively low-energy electrons. We have implemented a physical model for electron transport down to low energy in solid metallic media that meets both of the aforementioned requirements. The main goal of this paper is to present the theoretical framework of our Monte Carlo simulation, its application to gold metal and an extensive comparison with available data for gold foils irradiated by electron beams, for projectile energies ranging from a few eV to 90 keV. In particular, we calculated secondary electron emission to assess the accuracy of our code at energies below 50 eV. A close agreement with experiment is obtained for a large range of energy, even though the backward emission yields of low-energy electron are systematically underestimated. Nevertheless, the quality and numerical efficiency of the simulation are encouraging for nanoscale applications such as nanodosimetry or radiochemistry in presence of gold nanoparticles