| 1. |
- Assie, M., et al.
(författare)
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Neutron correlations in 6He viewed through nuclear break-up
- 2010
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Ingår i: Modern Physics Letters A. - 0217-7323 .- 1793-6632. ; 25:21-23, s. 1846-1849
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear break-up as a tool to study neutron correlations is investigated both theoretically and experimentally. First a time dependent theory going beyond mean field has been developed and shows that correlations between nucleons can be probed through nuclear break-up. Secondly, nuclear break-up of He-6 on Pb-208 target was studied at 20 A.MeV using a secondary beam of He-6 produced by the SPIRAL facility at GANIL. From the correlation function, a strong contribution of the di-neutron configuration of He-6 is found.
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| 2. |
- Lemasson, A., et al.
(författare)
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Pair and single neutron transfer with Borromean He-8
- 2011
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 697:5, s. 454-458
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Tidskriftsartikel (refereegranskat)abstract
- Direct observation of the survival of Au-199 residues after 2n transfer in the He-8 + Au-197 system and the absence of the corresponding Cu-67 in the He-8 + Cu-65 system at various energies are reported. The measurements of the surprisingly large cross sections for Au-199, coupled with the integral cross sections for the various Au residues, is used to obtain the first model-independent lower limits on the ratio of 2n to in transfer cross sections from He-8 to a heavy target. A comparison of the transfer cross sections for He-6.8 on these targets highlights the differences in the interactions of these Borromean nuclei. These measurements for the most neutron-rich nuclei on different targets highlight the need to probe the reaction mechanism with various targets and represent an experimental advance towards understanding specific features of pairing in the dynamics of dilute nuclear systems.
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| 3. |
- Lemasson, A., et al.
(författare)
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Reactions with the double-Borromean nucleus 8He
- 2010
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 82:4, s. 044617-
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Tidskriftsartikel (refereegranskat)abstract
- Differential cross sections for elastic-scattering and neutron-transfer reactions along with cross sections for fusion in the He-8+Cu-65 system are reported at energies above the Coulomb barrier (E-lab = 19.9 and 30.6 MeV). The present work demonstrates the feasibility of using inclusive measurements of characteristic in-beam gamma rays with low-intensity (similar to 10(5) pps) radioactive ion beams to obtain the residue cross sections for fusion and neutron transfer. Exclusive measurements of gamma rays in coincidence with light charged particles have been used to further characterize the direct reactions induced by this double-Borromean nucleus. Coupled reaction channels calculations are used to illustrate the important role played by the transfer channels and to help in understanding the influence of the structure of He-8 on the reaction mechanism.
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| 4. |
- Aramburo, Luis R., et al.
(författare)
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The Porosity, Acidity, and Reactivity of Dealuminated Zeolite ZSM-5 at the Single Particle Level : The Influence of the Zeolite Architecture
- 2011
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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 17:49, s. 13773-13781
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Tidskriftsartikel (refereegranskat)abstract
- A combination of atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), focused-ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron-based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM-5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol-to-olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM-5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM-5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 550 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Bronsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.
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| 5. |
- Charity, R. J., et al.
(författare)
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Two-proton decay of the 6Be ground state and the double isobaric analog of 11Li
- 2013
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 420:1
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Konferensbidrag (refereegranskat)abstract
- Two-proton decay is discussed in a number of light isobaric multiplets. For the lightest two-proton emitter, 6Be, the momentum correlations between the three decay products were measured and found to be consistent with quantum-mechanical three-cluster-model calculations. Two-proton decay was also found for two members of the A=8 and A=11 quintets. Finally, a third member of the A=11 sextet, the double isobaric analog of the halo nucleus 11Li in 11B was observed by its two-proton decay.
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| 6. |
- Vigren, E., et al.
(författare)
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On the thermal electron balance in Titan's sunlit upper atmosphere
- 2013
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 223:1, s. 234-251
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Tidskriftsartikel (refereegranskat)abstract
- The Cassini mission has investigated Titan's upper atmosphere in detail and found that, under solar irradiation, it has a well-developed ionosphere, which peaks between 1000 and 1200km. In this paper we focus on the T40, T41, T42 and T48 Titan flybys by the Cassini spacecraft and use in situ measurements of N2 and CH4 densities by the Ion Neutral Mass Spectrometer (INMS) as input into a solar energy deposition model to determine electron production rates. We combine these electron production rates with estimates of the effective recombination coefficient based on available laboratory data for Titan ions' dissociative recombination rates and electron temperatures derived from the Langmuir probe (LP) to predict electron number densities in Titan's upper atmosphere, assuming photochemical equilibrium and loss of electrons exclusively through dissociative recombination with molecular ions. We then compare these predicted electron number densities with those observed in Titan's upper atmosphere by the LP. The assumption of photochemical equilibrium is supported by a reasonable agreement between the altitudes where the electron densities are observed to peak and where the electron production rates are calculated to peak (roughly corresponding to the unit optical depth for HeII photons at 30.38nm). We find, however, that the predicted electron number densities are nearly a factor of two higher than those observed throughout the altitude range between 1050 and 1200km (where we have made estimates of the effective recombination coefficient). There are different possible reasons for this discrepancy; one possibility is that there may be important loss processes of free electrons other than dissociative recombination in Titan's upper atmosphere.
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