| 1. |
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| 2. |
- De Oliveira Santos, F., et al.
(författare)
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Study of 19Na at SPIRAL
- 2005
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 24:2, s. 237-247
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Tidskriftsartikel (refereegranskat)abstract
- The excitation function for the elastic-scattering reaction p( 18 Ne, p) 18 Ne was measured with the first radioactive beam from the SPIRAL facility at the GANIL laboratory and with a solid cryogenic hydrogen target. Several broad resonances have been observed, corresponding to new excited states in the unbound nucleus 19 Na. In addition, two-proton emission events have been identified and are discussed.
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| 3. |
- de Walle, J. V., et al.
(författare)
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Coulomb excitation of the N=50 nucleus Zn-80
- 2008
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Ingår i: AIP Conference Proceedings. - 1551-7616 .- 0094-243X. ; 1012, s. 291-295 453
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Konferensbidrag (refereegranskat)abstract
- Neutron rich Zinc isotopes, including the N=50 nucleus Zn-80, were produced and post-accelerated at the Radioactive Ion Beam (RIB) facility REX-ISOLDE (CERN). Low-energy Coulomb excitation was induced on these isotopes after post-acceleration, yielding B(E2) strengths to the first excited 2(+) states. For the first time, an excited state in Zn-80 was observed and the 2(1)(+) state in Zn-78 was established. The measured B(E2,2(1)(+) -> 0(1)(+)) values are compared to two sets of large scale shell model calculations. Both calculations reproduce the observed B(E2) systematics for the full Zinc isotopic chain. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni-78.
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| 4. |
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| 5. |
- Mach, Henryk, et al.
(författare)
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Ultrafast-timing lifetime measurements in Ru-94 and Pd-96 : Breakdown of the seniority scheme in N=50 isotones
- 2017
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Ingår i: PHYSICAL REVIEW C. - : American Physical Society. - 2469-9985. ; 95:1
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Tidskriftsartikel (refereegranskat)abstract
- The advanced time-delayed gamma gamma(t) method has been applied to determine half-lives of low-lying states in the N = 50 isotones Ru-94 and Pd-96. The inferred experimental E2 strengths for the 4(+) -> 2(+) transitions in the two nuclei show a dramatic deviation with respect to the shell model predictions in the (f(5/2), p, g(9/2)) proton hole space in Sn-100. The anomalous behavior can be ascribed to a breakdown of the seniority quantum number in the pi g(9/2)(n) configuration due to particle-hole excitations across the N = Z = 50 shell as confirmed by large-scale shell model calculations.
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| 6. |
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| 7. |
- Van de Walle, J., et al.
(författare)
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Coulomb excitation of neutron-rich Zn isotopes: First observation of the 2(1)(+) state in Zn-80
- 2007
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Ingår i: Physical Review Letters. - 1079-7114. ; 99:14
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)(+) state in Zn-78 could be firmly established and for the first time the 2(+)-> 0(1)(+) transition in Zn-80 was observed at 1492(1) keV. B(E2,2(1)(+)-> 0(1)(+)) values were extracted for Zn-74,Zn-76,Zn-78,Zn-80 and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, Zn-80 is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus Ni-78.
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| 8. |
- Van de Walle, J., et al.
(författare)
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Low-energy Coulomb excitation of neutron-rich zinc isotopes
- 2009
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 79:1
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Tidskriftsartikel (refereegranskat)abstract
- At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2, 2(1)(+)-> 0(1)(+)) values in Zn74-80, B(E2, 4(1)(+)-> 2(1)(+)) values in Zn-74,Zn-76 and the determination of the energy of the first excited 2(1)(+) states in Zn-78,Zn-80. The zinc isotopes were produced by high-energy proton- (A = 74, 76, 80) and neutron-(A = 78) induced fission of U-238, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondary target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N = 50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.
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| 9. |
- Walle, J. Van de, et al.
(författare)
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Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the 2[sub 1][sup +] State in [sup 80]Zn
- 2007
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Ingår i: Physical Review Letters. ; 99:14, s. 142501-
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 21+ state in 78Zn could be firmly established and for the first time the 2+-->01+ transition in 80Zn was observed at 1492(1) keV. B(E2,21+-->01+) values were extracted for 74,76,78,80Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization. The new results serve as benchmarks to establish theoretical models, predicting the nuclear properties of the doubly magic nucleus 78Ni.
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| 10. |
- Brüchert, Volker, et al.
(författare)
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Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment
- 2018
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 15:2, s. 471-490
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Tidskriftsartikel (refereegranskat)abstract
- The Siberian Arctic Sea shelf and slope is a key region for the degradation of terrestrial organic material transported from the organic carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O2 microelectrode profiling, intact sediment core incubations, 35 S-sulfate tracer experiments, porewater dissolved inorganic carbon (DIC), δ13 CDIC, and iron, manganese, and ammonium concentrations from 20 shelf and slope stations. This data set provides a spatial overview of sediment carbon mineralization rates and pathways over large parts of the outer Laptev and East Siberian Arctic shelf and slope, and allowed us to assess degradation rates and efficiency of carbon burial in these sediments. Rates of oxygen uptake and iron and manganese reduction were comparable to temperate shelf and slope environments, but bacterial sulfate reduction rates were comparatively low. In the topmost 20 to 50 cm of sediment, aerobic carbon mineralization dominated degradation and comprised on average 82% of the depthintegrated carbon mineralization. Oxygen uptake rates and 35 S-sulfate reduction rates were higher in the eastern East Siberian Sea shelf compared to the Laptev Sea shelf. DIC/NH4 + ratios in porewaters and the stable carbon isotope composition of remineralized DIC indicated that the degraded organic matter on the Siberian shelf and slope was a mixture of marine and terrestrial organic matter. Based on dual end member calculations, the terrestrial organic carbon contribution varied between 32% and 36%, with a higher contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation of the measured degradation rates using isotope end member apportionment over the outer shelf of the Laptev and East Siberian Sea suggests that about 16 Tg C per year are respired in the outer shelf sea floor sediment. Of the organic matter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C per year are degraded by anaerobic processes, with a terrestrial organic carbon contribution ranging between 0.3 and 0.5 Tg per year.
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| 11. |
- Grawe, H, et al.
(författare)
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Experimental approach towards shell structure at Sn-100 and Ni-78
- 2002
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Ingår i: Nuclear Physics, Section A. - 0375-9474. ; 704, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- The status of experimental approach to Sn-100 and Ni-78 is reviewed. Revised single particle energies for neutrons are deduced for the N=Z=50 shell closure and evidence for low lying I-pi=2(+) and 3(-) states is presented. Moderate E2 polarization charges of 0.1 e and 0.6 e are found to reproduce the experimental data when core excitation of Sn-100 is properly accounted for in the shell model. For the neutron rich Ni region no conclusive evidence for an N=40 subshell is found, whereas firm evidence for the persistence of the N=50 shell at Ni-78 is inferred from the existence of seniority isomers. The disappearance of this isomerism in the mid nug(9/2) shell is discussed.
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| 12. |
- Robador, Alberto, et al.
(författare)
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Activity and community structures of sulfate-reducing microorganisms in polar, temperate and tropical marine sediments
- 2016
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 10:4, s. 796-809
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Tidskriftsartikel (refereegranskat)abstract
- Temperature has a fundamental impact on the metabolic rates of microorganisms and strongly influences microbial ecology and biogeochemical cycling in the environment. In this study, we examined the catabolic temperature response of natural communities of sulfate-reducing microorganisms (SRM) in polar, temperate and tropical marine sediments. In short-term sediment incubation experiments with S-35-sulfate, we demonstrated how the cardinal temperatures for sulfate reduction correlate with mean annual sediment temperatures, indicating specific thermal adaptations of the dominant SRM in each of the investigated ecosystems. The community structure of putative SRM in the sediments, as revealed by pyrosequencing of bacterial 16S rRNA gene amplicons and phylogenetic assignment to known SRM taxa, consistently correlated with in situ temperatures, but not with sediment organic carbon concentrations or C:N ratios of organic matter. Additionally, several species-level SRM phylotypes of the class Deltaproteobacteria tended to co-occur at sites with similar mean annual temperatures, regardless of geographic distance. The observed temperature adaptations of SRM imply that environmental temperature is a major controlling variable for physiological selection and ecological and evolutionary differentiation of microbial communities.
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| 13. |
- Sawicka, Joanna E., et al.
(författare)
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Annual variability and regulation of methane and sulfate fluxes in Baltic Sea estuarine sediments
- 2017
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14:2, s. 325-339
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Tidskriftsartikel (refereegranskat)abstract
- Marine methane emissions originate largely from near-shore coastal systems, but emission estimates are often not based on temporally well-resolved data or sufficient understanding of the variability of methane consumption and production processes in the underlying sediment. The objectives of our investigation were to explore the effects of seasonal temperature, changes in benthic oxygen concentration, and historical eutrophication on sediment methane concentrations and benthic fluxes at two type localities for open-water coastal versus eutrophic, estuarine sediment in the Baltic Sea. Benthic fluxes of methane and oxygen and sediment pore-water concentrations of dissolved sulfate, methane, and S-35-sulfate reduction rates were obtained over a 12-month period from April 2012 to April 2013. Benthic methane fluxes varied by factors of 5 and 12 at the offshore coastal site and the eutrophic estuarine station, respectively, ranging from 0.1 mmol m(-2) d(-1) in winter at an open coastal site to 2.6 mmol m(-2) d(-1) in late summer in the inner eutrophic estuary. Total oxygen uptake (TOU) and S-35-sulfate reduction rates (SRRs) correlated with methane fluxes showing low rates in the winter and high rates in the summer. The highest pore-water methane concentrations also varied by factors of 6 and 10 over the sampling period with the lowest values in the winter and highest values in late summerearly autumn. The highest pore-water methane concentrations were 5.7 mM a few centimeters below the sediment surface, but they never exceeded the in situ saturation concentration. Of the total sulfate reduction, 21-24% was coupled to anaerobic methane oxidation, lowering methane concentrations below the sediment surface far below the saturation concentration. The data imply that bubble emission likely plays no or only a minor role in methane emissions in these sediments. The changes in pore-water methane concentrations over the observation period were too large to be explained by temporal changes in methane formation and methane oxidation rates due to temperature alone. Additional factors such as regional and local hydrostatic pressure changes and coastal submarine groundwater flow may also affect the vertical and lateral transport of methane.
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| 14. |
- Sawicka, Joanna E., et al.
(författare)
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Effects of freeze-thaw cycles on anaerobic microbial processes in an Arctic intertidal mud flat
- 2010
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Ingår i: ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4:4, s. 585-594
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Tidskriftsartikel (refereegranskat)abstract
- Insight into the effects of repeated freezing and thawing on microbial processes in sediments and soils is important for understanding sediment carbon cycling at high latitudes acutely affected by global warming. Microbial responses to repeated freeze-thaw conditions were studied in three complementary experiments using arctic sediment collected from an intertidal flat that is exposed to seasonal freeze-thaw conditions (Ymerbukta, Svalbard, Arctic Ocean). The sediment was subjected to oscillating freeze-thaw incubations, either gradual, from -5 to 4 degrees C, or abrupt, from -20 to 10 degrees C. Concentrations of low-molecular weight carboxylic acids (volatile fatty acids) were measured and sulfate reduction was assessed by measuring S-35 sulfate reduction rates (SRRs). Gradual freeze-thaw incubation decreased microbial activity in the frozen state to 0.25 % of initial levels at 4 degrees C, but activity resumed rapidly reaching >60 % of initial activity in the thawed state. Exposure of sediments to successive large temperature changes (-20 versus 10 degrees C) decreased SRR by 80% of the initial activity, suggesting that a fraction of the bacterial community recovered rapidly from extreme temperature fluctuations. This is supported by 16S rRNA gene-based denaturing gradient gel electrophoresis profiles that revealed persistence of the dominant microbial taxa under repeated freeze-thaw cycles. The fast recovery of the SRRs suggests that carbon mineralization in thawing arctic sediment can resume without delay or substantial growth of microbial populations.
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| 15. |
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| 16. |
- Sawicka, Joanna E., et al.
(författare)
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Temperature characteristics of bacterial sulfate reduction in continental shelf and slope sediments
- 2012
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 9:8, s. 3425-3435
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Tidskriftsartikel (refereegranskat)abstract
- The temperature responses of sulfate-reducing microbial communities were used as community temperature characteristics for their in situ temperature adaptation, their origin, and dispersal in the deep sea. Sediments were collected from a suite of coastal, continental shelf, and slope sediments from the southwest and southeast Atlantic and permanently cold Arctic fjords from water depths ranging from the intertidal zone to 4327 m. In situ temperatures ranged from 8 A degrees C on the shelf to -1 A degrees C in the Arctic. Temperature characteristics of the active sulfate-reducing community were determined in short-term incubations with S-35-sulfate in a temperature gradient block spanning a temperature range from 0 to 40 A degrees C. An optimum temperature (T-opt) between 27 A degrees C and 30 A degrees C for the South Atlantic shelf sediments and for the intertidal flat sediment from Svalbard was indicative of a psychrotolerant/mesophilic sulfate-reducing community, whereas T-opt < 20 A degrees C in South Atlantic slope and Arctic shelf sediments suggested a predominantly psychrophilic community. High sulfate reduction rates (20-50%) at in situ temperatures compared to those at T-opt further support this interpretation and point to the importance of the ambient temperature regime for regulating the short-term temperature response of sulfate-reducing communities. A number of cold (< 4 A degrees C) continental slope sediments showed broad temperature optima reaching as high as 30 A degrees C, suggesting the additional presence of apparently mesophilic sulfate-reducing bacteria. Since the temperature characteristics of these mesophiles do not fit with the permanently cold deep-sea environment, we suggest that these mesophilic microorganisms are of allochthonous origin and transported to this site. It is likely that they were deposited along with the mass-flow movement of warmer shelf-derived sediment. These data therefore suggest that temperature response profiles of bacterial carbon mineralization processes can be used as community temperature characteristics, and that mixing of bacterial communities originating from diverse locations carrying different temperature characteristics needs to be taken into account to explain temperature response profiles of bacterial carbon mineralization processes in sediments.
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| 17. |
- Schlegel, C, et al.
(författare)
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K-isomers in very neutron-rich nuclei around mass 180
- 2000
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Ingår i: Physica Scripta. Topical Issues. - 0281-1847. ; T88, s. 72-76
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Tidskriftsartikel (refereegranskat)abstract
- gamma-spectroscopy methods have been used to search for microsecond isomers among the fragmentation products of a 1 GeV/nucleon Pb-208 beam. In particular the population of the known K-pi = 35/2(-) isomer in W-179 has been investigated and several new isomeric decays have been found for neutron rich nuclei in the A approximate to 180-200 mass region. The ground state band of the neutron rich N = 116 system of W-190 has been identified for the first time and we discuss its structure in comparison to neighboring systems.
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