831 research outputs found
Investigation of slow collisions for (quasi) symmetric heavy systems: what can be extracted from high resolution X-ray spectra
We present a new experiment on (quasi) symmetric collision systems at
low-velocity, namely Ar ions ( a.u.) on gaseous Ar and N
targets, using low- and high-resolution X-ray spectroscopy. Thanks to an
accurate efficiency calibration of the spectrometers, we extract absolute X-ray
emission cross sections combining low-resolution X-ray spectroscopy and a
complete determination of the ion beam - gas jet target overlap. Values with
improved uncertainty are found in agreement with previous results
\cite{Tawara2001}. Resolving the whole He-like Ar Lyman series from
to 10 with our crystal spectrometer enables to determine precisely the
distribution of the electron capture probability and the
preferential level of the selective single-electron capture.
Evaluation of cross sections for this process as well as for the contribution
of multiple-capture is carried out. Their sensitivity to the
-distribution of levels populated by single-electron capture is
clearly demonstrated, providing a stringent benchmark for theories. In
addition, the hardness ratio is extracted and the influence of the decay of the
metastable state on this ratio is discussed
PHYSICAL PARAMETER DEPENDENCE OF THE X-RAY GENERATION IN INTENSE LASER – CLUSTER INTERACTION
International audienceStudies on laser – cluster interaction performed on the LUCA facility (French acronym for Ultra Short Tunable Laser, CEA Saclay) allow to observe the production of hard x-rays in the 1 to 5 keV range when rare gas clusters of nanometer sizes are heated by strong optical fields (F > 10^9 V/cm). First complete quantitative measurements of absolute photon emission yields, as well as of charge state distributions of ionic species with inner shell vacancies have been performed as a function of several physical parameters governing the interaction. Our measurements give rise to fundamental results like an optimum heating time and an intensity threshold in the x-ray production. These data provide direct insight into the interaction dynamics and into the heating processes involved
Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions
Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet, Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996)10.1016/0168-583X(95)00800-4], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by 28.9MeVu-1Pb56+ ions, and laser-generated carbon ion beams of 0.045 to 0.5MeVu-1, passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the "next-generation" accelerators or laser facilities.Fil: Lamour, E.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Fainstein, Pablo Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. ComisiĂłn Nacional de EnergĂa AtĂłmica. Centro AtĂłmico Bariloche; ArgentinaFil: Galassi, Mariel Elisa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de FĂsica de Rosario. Universidad Nacional de Rosario. Instituto de FĂsica de Rosario; ArgentinaFil: Prigent, C.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Ramirez, C. A.. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de FĂsica de Rosario. Universidad Nacional de Rosario. Instituto de FĂsica de Rosario; ArgentinaFil: Rivarola, Roberto Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de FĂsica de Rosario. Universidad Nacional de Rosario. Instituto de FĂsica de Rosario; ArgentinaFil: Rozet, J. P.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Trassinelli, M.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Vernhet, D.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; Franci
KHT cold stabilization: A scanning electron microscopy study of the formation of surface deposits on stainless steel in model wines
The incidence of yeast cells and wine polysaccharides and polyphenols in the formation of adherent KHT crystals on stainless steel surfaces during cold stabilization was investigated by scanning electron microscopy. Additives were responsible for differences in the deposit configuration, the crystal shape and size as well as in the KHT crystallization kinetics. Yeast cells act as heterogeneous primary nucleation germs for KHT crystal formation. Colloids from wines interacted with KHT crystal faces and affected growth. It was confirmed that polyphenols strongly inhibit the crystallization and result in small crystals with a unidimensional growth. In contrast, with polyphenols, cubic crystals were obtained when wine polysaccharides were associated with yeast cells
Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation
Magnetic refrigeration based on the magnetocaloric effect at room temperature
is one of the most attractive alternative to the current gas
compression/expansion method routinely employed. Nevertheless, in giant
magnetocaloric materials, optimal refrigeration is restricted to the narrow
temperature window of the phase transition (Tc). In this work, we present the
possibility of varying this transition temperature into a same giant
magnetocaloric material by ion irradiation. We demonstrate that the transition
temperature of iron rhodium thin films can be tuned by the bombardment of ions
of Ne 5+ with varying fluences up to 10 14 ions cm --2 , leading to optimal
refrigeration over a large 270--380 K temperature window. The Tc modification
is found to be due to the ion-induced disorder and to the density of new
point-like defects. The variation of the phase transition temperature with the
number of incident ions opens new perspectives in the conception of devices
using giant magnetocaloric materials
Suppression of the thermal hysteresis in magnetocaloric MnAs thin film by highly charged ion bombardment
We present the investigation on the modifications of structural and magnetic
properties of MnAs thin film epitaxially grown on GaAs induced by slow highly
charged ions bombardment under well-controlled conditions. The ion-induced
defects facilitate the nucleation of one phase with respect to the other in the
first-order magneto-structural MnAs transition with a consequent suppression of
thermal hysteresis without any significant perturbation on the other structural
and magnetic properties. In particular, the irradiated film keeps the giant
magnetocaloric effect at room temperature opening new perspective on magnetic
refrigeration technology for everyday use
A linear polar molecule in a two-color laser field: a symmetry analysis
We describe the field-dressed rotational dynamics of a linear polar molecule in a a non-resonant
two-color cw laser field, and analyze the orientation and alignment as the field parameters are varied
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