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[en] The U, Th, and 4He contents of meliphanite correspond to an age of metamorphism (1800 Ma) indicating good preservation of radiogenic 4He in mineral but contradicting the experience of U–Th–4He dating. For the analysis of this result, we studied preservation of 3He, which was found to be very low (~2%). The 3,4He isotopes occur in radiation tracks, the intersection of which with cleavage planes provide for their migration from the mineral. Thus, 4He originated from U and Th decay should be completely lost. Meliphanite entraps He, which probably occurs in specific volumes of its crystal structure. Extraction of He isotopes from meliphanite upon vacuum heating supports this conclusion. Application of only one U–Th–4He system for dating (as often applied in thermochronology) may yield erroneous results. Identification of the origin of He in minerals requires using both isotopes (3He and 4He).
[en] This thesis covers the isotopic analysis of carbon-rich interplanetary dust (ultra-carbonaceous micro-meteorites), in order to better understand the isotopic fractionation process of light elements (hydrogen and nitrogen) observed in the organic phases of primitive extraterrestrial matter. It is possible, within a collection of micro-meteorites coming from the central regions of the Antarctic continent, to identify ultra-carbonaceous micro-meteorites (UCAMMs - for Ultra-Carbonaceous Antarctic Micro-Meteorites) which contain about ten times more carbon than the primitive meteorites. These particles are extremely rare and open the possibility to study in laboratory cometary particles of large sizes (100-200 microns). This thesis focuses on the isotopic analyses of UCAMMs, in order to understand the isotopic fractionation processes of light elements (hydrogen and nitrogen) observed in the organic matter of the primitive solar system. Mineralogical, chemical and structural analyses on two fragments of ultra-carbonaceous micro-meteorites were performed in the framework of collaborations using techniques of scanning electron microscopy, electron microprobe, infrared microspectroscopy (SOLEIL synchrotron). The main work of this thesis concerns the isotopic analysis of two UCAMMs by Secondary Ion Mass Spectrometry (SIMS) using the NanoSIMS ion microprobe. The instrumental developments performed in collaboration between the CSNSM and the Curie Institute teams allow to resolve molecular interferences with a mass resolving power higher than 20 000 retaining a sensibility compatible with the measurements considered here. So, it has been possible to measure for the first time the hydrogen isotopic composition with the polyatomic ions 12C2D- and 12C2H- and to compare its spatial distribution with that of the nitrogen (12C15N-/12C14N-) obtained on the same surface with the same magnetic field. A protocol for producing a series of standard samples was developed from polymers isotopically enriched in deuterium in order to determine the instrumental fractionation of the NanoSIMS showing the possibility to perform precise measurements of the hydrogen isotopic composition in the organic matter (OM) with polyatomic ions (12CD-/12CH- and 12C2D- /12C2H- ratios). The isotopic maps at high spatial resolution (200 nm) in 12C2D-/12C2H- and 12C15N-/12C14N- show a very heterogeneous distribution in deuterium with extreme values going up to 20 times the terrestrial ocean value, whereas the 15N/14N ratios remain globally close (within 20%) to the terrestrial atmosphere value. Measurements of N/C ratios in ion imaging performed at the NanoSIMS confirm the values measured by electron microprobe and show that the OM of UCAMMs is rich in nitrogen. Comparisons between isotopic images with each other and with the images obtained by the other techniques show that the OM of UCAMMs is constituted of different components. The main component does not exhibit a clear correlation between the D and 15N excesses. A minor component of the analyzed surface exhibits correlated excesses in D and in 15N, without neither the elemental or structural composition of this component significantly differs from the rest of the grain. A minor component showing moderate enrichments in D and 15N/14N ratios lower than the terrestrial atmosphere value is identified. The data can be explained assuming that the ultra-carbonaceous micro-meteorites come from the surface of trans-neptunian icy objects. The isotopic characteristics observed in the OM of UCAMMs might result from the mixing of different precursors induced by the irradiation of the parent body by the galactic cosmic radiation at large heliocentric distances. (author)
[fr]Cette these porte sur l'analyse isotopique de poussieres interplanetaires riches en carbone (des micrometeorites ultracarbonees), pour mieux comprendre les processus de fractionnement isotopique des elements legers (hydrogene et azote) observes dans les phases organiques de la matiere extraterrestre primitive. Il est possible, au sein d'une collection de micrometeorites provenant des regions centrales du continent Antarctique, d'identifier des micrometeorites ultracarbonees (UCAMMs - pour Ultra-Carbonaceous Antarctic Micro-Meteorites) qui contiennent environ dix fois plus de carbone que les meteorites primitives. Ces particules rares (environ 1% des particules collectees) ouvrent la possibilite d'etudier en laboratoire des particules cometaires de grandes tailles (100-200 microns). Des analyses mineralogiques, chimiques et structurales sur deux fragments de micrometeorites ultracarbonees ont ete realisees dans le cadre de collaborations a l'aide de techniques de microscopie electronique a balayage, microsonde electronique, microspectroscopie infrarouge (synchrotron SOLEIL). Le travail principal de cette these concerne l'analyse isotopique de deux UCAMMs par spectrometrie de masse a emission ionique secondaire (SIMS) a l'aide de la microsonde ionique NanoSIMS. Les developpements instrumentaux effectues en collaboration entre les equipes du CSNSM et de l'Institut Curie permettent de resoudre les interferences moleculaires avec un pouvoir de separation en masse superieur a 20 000 en conservant une sensibilite compatible avec les mesures envisagees. Ainsi, il a ete possible de mesurer pour la premiere fois la composition isotopique de l'hydrogene avec les ions polyatomiques 12C2D- et 12C2H- et de comparer sa distribution spatiale avec celle de l'azote (12C15N-/12C14N-) obtenue sur la meme surface avec le meme champ magnetique. Un protocole de fabrication d'une serie d'echantillons standards a ete developpe a partir de polymeres isotopiquement marques en deuterium afin de determiner le fractionnement instrumental du NanoSIMS demontrant la possibilite d'effectuer des mesures precises de la composition isotopique de l'hydrogene dans la matiere organique (MO) avec des ions polyatomiques (rapports 12CD-/12CH- et 12C2D- /12C2H-). Les cartographies isotopiques a haute resolution spatiale (200 nm) en 12C2D-/12C2H- et 12C15N-/12C14N- montrent une distribution tres heterogene du deuterium avec des valeurs extremes allant jusqu'a 20 fois la valeur des oceans terrestres, alors que les rapports 15N/14N restent globalement proches (a 20% pres) de la valeur de l'atmosphere terrestre. Les mesures des rapports N/C effectuees en imagerie ionique au NanoSIMS confirment les valeurs mesurees par microsonde electronique et montrent que la MO des UCAMMs est riche en azote. Les comparaisons des images isotopiques entre elles et avec les images obtenues par les autres techniques montrent que la MO des UCAMMs est constituee de differents composants. Le composant principal ne montre pas de correlation marquee entre les exces en D et ceux en 15N. Une fraction mineure de la surface analysee montre des exces correles en D et en 15N, sans que la composition elementaire ni la structure de cette composante ne different significativement du reste de la particule. Une seconde composante mineure presente des enrichissements moderes en D et des rapports 15N/14N inferieurs a la valeur de l'atmosphere terrestre. L'ensemble des donnees peut etre explique en supposant que les micrometeorites ultracarbonees proviennent de la surface d'objets glaces transneptuniens. Les caracteristiques isotopiques observees dans la MO des UCAMMs pourraient resulter du melange de differents precurseurs synthetises a la surface du corps parent lors de son irradiation par le rayonnement cosmique galactique a grandes distances heliocentriques. (auteur)
[en] Full text: A main task in the study of nuclear reactions is to understand the nucleus-nucleus interaction. A phenomenological interaction potential, i.e. the optical potential, is universally adopted to describe the interaction of nuclear collisions. For tightly-bound nuclear systems, optical potentials show a threshold anomaly behavior at energies around the Coulomb barrier, which can be explained well by the dispersion relation. For weakly-bound nuclear systems, however, optical potentials show a different behavior, the so-called breakup threshold anomaly, which is not yet understood both experimentally and theoretically. To this end, angular distributions of elastic scattering and one-proton stripping reaction for the 7Li+208Pb systems have been measure at energies around the Coulomb barrier as well as well-below the barrier by using the Q3D magnet spectrograph and silicon-strip detector array, respectively. Optical potentials for the 7Li+208Pb system were extracted by fitting angular distributions of the incoming channel. After that, Optical potentials for the outgoing channel of 6He+209Bi were extracted with good precision by fitting angular distributions of 208Pb(7Li, 6He) reaction. The imaginary potentials increase when energies decrease below the barrier, and quickly drop down to zero at extremely low energy. The threshold energy was determined to about 13.7 MeV, which is corresponding to about 0.73 VB. This is the first time to determine the threshold energy for the weakly-bound system. Moreover, the traditional dispersion relation cannot describe the behavior of imaginary and real potentials. Some possible underlying physical reasons are pointed out. A new type of dispersion relation is strongly called for. Details of the experiment and analysis as well as discussions will be presented in the conference. (author)
[en] We investigate qualitative and quantitative projectile resonance effects on breakup and total fusion cross sections of the breakup of 6Li on 144Sm target. We show that these resonances exhibit opposite and slightly pronounced effects on the integrated breakup cross sections than on total fusion cross sections. It is obtained that, for energies above the Coulomb barrier, breakup cross sections are increased by the inclusion of these resonances, while fusion cross sections are reduced. We deduced that, on average, above the barrier, breakup cross sections are increased by , whereas fusion cross sections are suppressed by in the presence of the resonances.
[en] Due to technical constraints this article was published in volume 240:1 with erroneous article citation ID number 5 whereas this should have been 75 which is corrected as such. Springer Nature sincerely apologizes towards the author(s) for the inconvenience caused.
[en] We carry out investigations of inverted crossover resonances (ICRs) in π-driven four-level systems where can be zero. Through the use of sub-Doppler frequency modulation spectroscopy of the − transition in 171Yb the resonance becomes manifest. The centre frequency is inherently insensitive to first-order Zeeman shifts and equates to the two-level resonance frequency in the absence of a magnetic field. A rate equation model is used to help validate the nature of the resonance. Optical frequency measurements of the hyperfine line recorded over two months demonstrate a statistical uncertainty of 2 × 10−11. The ICR found with the line is used for 556 nm laser frequency stabilisation, which is an alternative means when applied to magneto-optical trapping of 171Yb. (paper)
[en] With the development of sophisticated pulsed field gradient- and phase cycling-approaches for suppressing certain coherence transfer pathways and selecting for others it is sometimes easy to forget that the process is not flawless. In some cases artifacts can emerge because unwanted transfers are immune to the phase cycle or the application of gradients. We consider here a simple 1H,13C HMQC pulse scheme and show that imperfections in the single 1H 180° refocusing pulse can give rise to small artifacts in methyl spectra that cannot be eliminated through extensive phase cycling or the use of gradients, but that are easily removed when the pulse is of the composite variety.
[en] Magnetic Feshbach resonances have allowed great success in the production of ultracold diatomic molecules from bi-alkali mixtures, but have so far eluded observation in mixtures of alkali and alkaline-earth-like atoms. Inelastic collisional properties of ultracold atomic systems exhibit resonant behavior in the vicinity of such resonances, providing a detection signature. We study magnetic field dependent inelastic effects via atom loss spectroscopy in an ultracold heteronuclear mixture of alkali 6Li in the ground state and alkaline-earth-like 174Yb in an excited electronic metastable state (3P2, ). We observe a variation of the interspecies inelastic two-body rate coefficient by nearly one order of magnitude over a 100–520 G magnetic field range. By comparing to ab initio calculations we link our observations to interspecies Feshbach resonances arising from anisotropic interactions in this novel collisional system. (paper)
[en] The behavior of COH fluids, their isotopes (hydrogen and carbon), and their interaction with magmatic liquids are at the core of understanding formation and evolution of the Earth. Experimental data are needed to aid our understanding of how COH volatiles affect rock-forming processes in the Earth’s interior. Here, I present a review of experimental data on structure of fluids and melts and an assessment of how structural factors govern hydrogen and carbon isotope partitioning within and between melts and fluids as a function of redox conditions, temperature, and pressure.The solubility of individual COH components in silicate melts can differ by several orders of magnitude and ranges from several hundred ppm to several wt%. Silicate solubility in fluid can reach several molecular at mantle temperatures and pressures. Different solubility of oxidized and reduced C-bearing species in melts reflects different solution equilibria. These equilibria are 2CH4 + Qn = 2CH3− + H2O + Qn + 1 and 2CO32− + H2O + 2Qn + 1 = HCO3− + 2Qn, under reducing and oxidizing conditions, respectively. In the Qn-notations, the superscript, n, denotes the number of bridging oxygen in the silicate species (Q-species).The structural changes of carbon and silicate in magmatic systems (melts and fluids) with variable redox conditions result in hydrogen and carbon isotope fractionation factors between melt, fluid, and crystalline materials that depend on redox conditions and can differ significantly from 1 even at magmatic temperatures. The ∆H of D/H fractionation between aqueous fluid and magma in silicate–COH systems is between − 5 and 25 kJ/mol depending on redox conditions. The ∆H values for 13C/12C fractionation factors are near − 3.2 and 1 kJ/mol under oxidizing and reducing conditions, respectively. These differences are because energetics of O–D, O–H, O–13C, and O–12C bonding environments are governed by different solution mechanisms in melts and fluids.From the above data, it is suggested that (COH)-saturated partial melts in the upper mantle can have δD values 100%, or more, lighter than coexisting silicate-saturated fluid. This effect is greater under oxidizing than under reducing conditions. Analogous relationships exist for 13C/12C. At magmatic temperatures in the Earth’s upper mantle, 13C/12C of melt in equilibrium with COH-bearing mantle in the − 7 to − 30‰ range increases with temperature from about 40 to > 100‰ and 80–120‰ under oxidizing and reducing conditions, respectively. .
[en] In this work we have studied the production of alpha particles emitted as a consequence of different reactions in the 7Li + 144Sm system at near-barrier energies. We have obtained absolute cross sections of the total yield at backward angles and at bombarding energies of 24 and 30 MeV. We have also performed complementary exclusive measurements of non-capture breakup processes at 30 MeV. In particular, the neutron transfer followed by non-capture breakup of the 6Li ejectile, which was found to be the dominant process in the studied region, could be accounted for by estimations of a classical dynamical model. This contribution, together with estimations for the incomplete fusion and alpha particle evaporation following compound-nucleus formation, are compared to the experimental inclusive angular distributions obtained in this work.