Etudes expérimentales de l'accélération de particules avec des lasers ultra-intenses (applications à des expériences de physique nucléaire dans les plasmas lasers)

Les lasers de puissance permettent depuis une dizaine d'années de produire des faisceaux de particules accélérées dans lesquels quelques 1012 électrons, protons sont accélérés en quelques ps. Nous avons simulé et développé des diagnostiques, utilisant l'activation nucléaire, pour qualifier les distributions angulaire et en énergie des faisceaux de particules générés. Les techniques de caractérisation sont présentées et illustrées à l'aide des résultats obtenus dans différentes expériences réalisées auprès des lasers de puissance. Nous envisageons d'utiliser ces faisceaux pour exciter des états nucléaires dans des environnements plasma. Celui-ci peut en effet influencer des caractéristiques intrinsèques du noyau comme la durée de vie de certains états isomériques. Dans le cadre de la préparation de telles expériences, nous avons mesuré la section efficace de la réaction (g,n) permettant de produire l'état isomérique du 84Rb à 463 keV d'énergie d'excitation, à l'aide de l'accélérateur ELSA du CEA/DIF de Bruyères-le-Châtel.Since the laser tens years, the Ultra High Intensity Laser offer the opportunities to produce accelerated particle beams with contain more than 1012 electrons, protons accelerated into few ps. We have simulated and developed some diagnostics based on the nuclear activation to characterize both the angular and the energy distribution of the particle beams produced with intense lasers. The characterization methods which are presented and illustrated by the means of results obtained in different experiments. We would use the particle beams produced to excite nuclear state in a plasma environment. It can modify intrinsic characteristics of the nuclei such as the half-life of some isomeric state. To prepare this kind of experiments, we have measured the nuclear reaction cross section (g,n) to produce the isomeric state of the 84Rb, which has an excitation energy around 463 keV, with the electron accelerator ELSA of CEA/DIF in Bruyères-le-Châtel.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Caractérisation de faisceaux de protons produits par laser via une analyse optique et nucléaire de films RCF

Generation of particle beams with high intensity lasers opens new domains of investigation both for fundamental and applied research. These beams are often characterized by means of radiochromic films (RCF) 1,2,3 which provide information both on their energy and spatial distributions. However the optical response function of these films for protons depends on their precise composition and is not well known making it difficult to extract absolute information on the number of particles contained in the beam. Proton induced nuclear reactions in RCF produce radioactive elements. The analysis of these activities allows to determine in a completely independent way the energy distribution of the proton beams 4,5. With the Monte Carlo simulation code Geant4, we have established the nuclear activation response function for different stacks of RCF films or RCF films and copper foils. We will present our method making use of the optical and nuclear activation responses of RCF and discuss the results obtained in the analysis of proton beams generated with the LULI 100 TW laser

NATALIE: A 32 detector integrated acquisition system to characterize laser produced energetic particles with nuclear techniques

We present a stand-alone system to characterize the high-energy particles emitted in the interaction of ultrahigh intensity laser pulses with matter. According to the laser and target characteristics, electrons or protons are produced with energies higher than a few mega electron volts. Selected material samples can, therefore, be activated via nuclear reactions. A multidetector, named NATALIE, has been developed to count the β+ activity of these irradiated samples. The coincidence technique used, designed in an integrated system, results in very low background in the data, which is required for low activity measurements. It, therefore, allows a good precision on the nuclear activation yields of the produced radionuclides. The system allows high counting rates and online correction of the dead time. It also provides, online, a quick control of the experiment. Geant4 simulations are used at different steps of the data analysis to deduce, from the measured activities, the energy and angular distributions of the laser-induced particle beams. Two applications are presented to illustrate the characterization of electrons and protons

Characterization of laser induced proton beams with radiochromic films: comparison between optical densitometry and nuclear activation analyses.

The generation of particle beams with high intensity lasers opens new domains of investigation both for fundamental and applied research. These beams are often characterised with radiochromic films (RCF) which provide information both on their energy and spatial distributions. However the optical response function of these films for protons depends on their precise composition and is not well known making it difficult to extract absolute information on the number of particles in the beam. Proton induced nuclear reactions in RCF produce radioactive elements. The analysis of these activities allows to determine in a completely independent way the energy distribution of the proton beams. Using the Monte Carlo simulation code Geant4, we have established the nuclear activation response functions for different stacks of RCF films and stacks of RCF films and copper foils. We will present our method based on the optical and nuclear activation responses of RCF and discuss the results obtained in the analysis of proton beams generated with the LULI 100 TW laser