Lifetimes of C-60(2-) and C-70(2-) dianions in a storage ring

C-60(2-) and C-70(2-) dianions have been produced by electrospray of the monoanions and subsequent electron pickup in a Na vapor cell. The dianions were stored in an electrostatic ring and their decay by electron emission was measured up to 1 s after injection. While C-70(2-) ions are stable on this time scale, except for a small fraction of the ions which have been excited by gas collisions, most of the C-60(2-) ions decay on a millisecond time scale, with a lifetime depending strongly on their internal temperature. The results can be modeled as decay by electron tunneling through a Coulomb barrier, mainly from thermally populated triplet states about 120 meV above a singlet ground state. At times longer than about 100 ms, the absorption of blackbody radiation plays an important role for the decay of initially cold ions. The tunneling rates obtained from the modeling, combined with WKB estimates of the barrier penetration, give a ground-state energy 200 +/- 30 meV above the energy of the monoanion plus a free electron and a ground-state lifetime of the order of 20 s. (c) 2006 American Institute of Physics

Measurement of the charged pion mass using X-ray spectroscopy of exotic atoms

The $5g-4f$ transitions in pionic nitrogen and muonic oxygen were measured simultaneously by using a gaseous nitrogen-oxygen mixture at 1.4\,bar. Due to the precise knowledge of the muon mass the muonic line provides the energy calibration for the pionic transition. A value of (139.57077\,$\pm$\,0.00018)\,MeV/c$^{2}$ ($\pm$\,1.3ppm) is derived for the mass of the negatively charged pion, which is 4.2ppm larger than the present world average

Hadronic shift in pionic hydrogen

The hadronic shift in pionic hydrogen has been redetermined to be $\epsilon_{1s}=7.086\,\pm\,0.007(stat)\,\pm\,0.006(sys)$\,eV by X-ray spectroscopy of ground state transitions applying various energy calibration schemes. The experiment was performed at the high-intensity low-energy pion beam of the Paul Scherrer Institut by using the cyclotron trap and an ultimate-resolution Bragg spectrometer with bent crystals.Comment: 10 pages, 6 figure

Ion induced fragmentation of biomolecular systems at low collision energies

In this paper, we present results of different collision experiments between multiply charged ions at low collision energies (in the keV-region) and biomolecular systems. This kind of interaction allows to remove electrons form the biomolecule without transferring a large amount of vibrational excitation energy. Nevertheless, following the ionization of the target, fragmentation of biomolecular species may occur. It is the main objective of this work to study the physical processes involved in the dissociation of highly electronically excited systems. In order to elucidate the intrinsic properties of certain biomolecules (porphyrins and amino acids) we have performed experiments in the gas phase with isolated systems. The obtained results demonstrate the high stability of porphyrins after electron removal. Furthermore, a dependence of the fragmentation pattern produced by multiply charged ions on the isomeric structure of the alanine molecule has been shown. By considering the presence of other surrounding biomolecules (clusters of nucleobases), a strong influence of the environment of the biomolecule on the fragmentation channels and their modification, has been clearly proven. This result is explained, in the thymine and uracil case, by the formation of hydrogen bonds between O and H atoms, which is known to favor planar cluster geometries.</p

Cryogenic Design of the 43 T LNCMI Grenoble Hybrid Magnet

AbstractThe association of two inner resistive coils (Polyhelix and Bitter) producing 34.5 T with an outer NbTi superconducting coil producing 8.5 T to obtain a 43 T hybrid magnet is a technical challenge. Accidental failure modes leading to complex electromagnetic behaviors and large transient dynamical forces should be anticipated. These considerations lead to a reinforced design and a thermo-hydraulic strategy to limit the overpressure. The cryostat has been designed with innovative thermo-mechanical supports sustaining the coil at 1.8 K-1200 hPa and the eddy current shield at 30 K, both being possibly overloaded by high dynamic forces in the worst accidental failure case

Fragmentation of α- and β-alanine molecules by ions at Bragg-peak energies

The interaction of keV He(+), He(2+), and O(5+) ions with isolated alpha and beta isomers of the amino acid alanine was studied by means of high resolution coincidence time-of-flight mass spectrometry. We observed a strong isomer dependence of characteristic fragmentation channels which manifests in strongly altered branching ratios. Despite the ultrashort initial perturbation by the incoming ion, evidence for molecular rearrangement leading to the formation of H(3)(+) was found. The measured kinetic energies of ionic alanine fragments can be sufficient to induce secondary damage to DNA in a biological environment. (C) 2008 American Institute of Physics

Study of ion emission from a germanium crystal surface under impact of fast Pb ions in channeling conditions

International audienceA thin germanium crystal has been irradiated at GANIL by Pb beams of 29 MeV/A (charge state Qin = 56 and 72) and of 5.6 MeV/A (Qin = 28). The induced ion emission from the sample entrance surface was studied, impact per impact, as a function of Qin, velocity vin and energy loss DE in the crystal. The Pb ions transmitted through the crystal were analyzed in charge (Qout) and energy using the SPEG spectrometer. The emitted ionized species were detected and analyzed in mass by a Time of Flight multianode detector (LAG). Channeling was used to select peculiar DE in Ge and hence peculiar Pb ion trajectories close to the emitting surface. The experiment was performed in standard vacuum. No Ge emission was found. The dominating emitted species are H+ and hydrocarbon ions originating from the contamination layer on top of the crystal. The mean value of the number of detected species per incoming Pb ion (multiplicity) varies as (Qin/vin)^p, with p values in agreement with previous results. We have clearly observed an influence of the energy deposition DE in Ge on the emission from the top contamination layer. When selecting increasing values of DE, we observed a rather slow increase of . On the contrary, the probabilities of high multiplicity values, that are essentially connected to fragmentation after emission, strongly increase with DE

Parâmetros produtivos de rebanhos leiteiros na regional Tarauacá/Envira - Acre.

O objetivo deste estudo foi estimar os parâmetros produtivos de propriedades leiteiras da regional Tarauacá/Envira