| 1. |
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| 2. |
- Bree, N, et al.
(författare)
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Shape Coexistence in the Neutron-Deficient Even-Even Hg182-188 Isotopes Studied via Coulomb Excitation.
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 112:16
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Tidskriftsartikel (refereegranskat)abstract
- Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85 MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0+ states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0+ state was noted in Hg182,184. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established.
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| 3. |
- Clément, E., et al.
(författare)
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Low-energy Coulomb excitation of Sr 96,98 beams
- 2016
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 94:5, s. 054326-
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Tidskriftsartikel (refereegranskat)abstract
- The structure of neutron-rich Sr96,98 nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N=60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in Sr98, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in Rb98 has been obtained.
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| 4. |
- Clément, E, et al.
(författare)
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Spectroscopic Quadrupole Moments in ^{96,98}Sr: Evidence for Shape Coexistence in Neutron-Rich Strontium Isotopes at N=60.
- 2016
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Ingår i: Physical Review Letters. - 1079-7114. ; 116:2
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Tidskriftsartikel (refereegranskat)abstract
- Neutron-rich ^{96,98}Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N=60.
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| 5. |
- Ekström, Andreas, et al.
(författare)
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Electric quadrupole moments of the 2(1)(+) states in Cd-100,Cd-102,Cd-104
- 2009
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 80:5
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Tidskriftsartikel (refereegranskat)abstract
- Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0(gs)(+)-> 2(1)(+) transition in the beta-unstable isotopes Cd-100,Cd-102,Cd-104 have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(2(1)(+)) in Cd-102,Cd-104. In addition to the B(E2) values in Cd-102,Cd-104, a first experimental limit for the B(E2) value in Cd-100 is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(2(1)(+)) values.
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| 6. |
- Wrzosek-Lipska, K., et al.
(författare)
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Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes : Coulomb excitation of 182Hg, 184Hg, 186Hg and 188Hg
- 2019
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 55:8
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of 01,2+, 21,2+ and 41+ states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions.
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| 7. |
- Ekström, Andreas, et al.
(författare)
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0(gs)+ -->2(1)+ transition strengths in 106Sn and 108Sn.
- 2008
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Ingår i: Physical Review Letters. - 1079-7114. ; 101:1
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Tidskriftsartikel (refereegranskat)abstract
- The reduced transition probabilities, B(E2; 0(gs)+ -->2(1)+), have been measured in the radioactive isotopes (108,106)Sn using subbarrier Coulomb excitation at the REX-ISOLDE facility at CERN. Deexcitation gamma rays were detected by the highly segmented MINIBALL Ge-detector array. The results, B(E2;0(gs)+ -->2(1)+)=0.222(19)e2b2 for 108Sn and B(E2; 0(gs)+-->2(1)+)=0.195(39)e2b2 for 106Sn were determined relative to a stable 58Ni target. The resulting B(E2) values are approximately 30% larger than shell-model predictions and deviate from the generalized seniority model. This experimental result may point towards a weakening of the N=Z=50 shell closure.
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| 8. |
- Ekström, Andreas, et al.
(författare)
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Coulomb excitation of the odd-odd isotopes In-106,In-108
- 2010
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Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001. ; 44:3, s. 355-361
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Tidskriftsartikel (refereegranskat)abstract
- The low-lying states in the odd-odd and unstable isotopes In-106,In-108 have been Coulomb excited from the ground state and the first excited isomeric state at the REX-ISOLDE facility at CERN. With the additional data provided here the pi g(9/2)(-1) circle times nu d(5/2) and pi g(9/2)(-1) circle times nu g7/2 multiplets have been re-analyzed and are modified compared to previous results. The observed gamma-ray de-excitation patterns were interpreted within a shell model calculation based on a realistic effective interaction. The agreement between theory and experiment is satisfactory and the calculations reproduce the observed differences in the excitation pattern of the two isotopes. The calculations exclude a 6(+) ground state in In-106. This is in agreement with the conclusions drawn using other techniques. Furthermore, based on the experimental results, it is also concluded that the ordering of the isomeric and ground state in In-108 is inverted compared to the shell model prediction. Limits on B(E2) values have been extracted where possible. A previously unknown low-lying state at 367 keV in In-106 is also reported.
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| 9. |
- Ekström, Andreas, et al.
(författare)
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Sub-barrier Coulomb excitation of Sn-106,Sn-108,Sn-110
- 2008
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Ingår i: Frontiers in Nuclear structure, Astrophysics and Reactions - Finustar 2, AIP Conference Proceedings. - : AIP. - 0094-243X .- 1551-7616. ; 1012, s. 296-299
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Konferensbidrag (refereegranskat)abstract
- The reduced transition probabilities between the first excited 2(+) state and the 0(+) ground state, B(E2; 0(+) -> 2(+)), have been measured in Sn-106,Sn-108,Sn-110 using sub-barrier Coulomb excitation in inverse kinematics at REX-ISOLDE. The results are, B(E2;0(+) -> 2(+)) = 0.220(22),0.226(17), and 0.228(32) e(2)b(2), for Sn-110, Sn-108, and Sn-106, respectively. The results for Sn-106,Sn-108 are preliminary. De-excitation gamma-rays were detected by the MINIBALL Ge-array. The B(E2) reveals detailed information about the nuclear wave function. A shell model prediction based on an effective CD-Bonn interaction in the nu(0g(7/2),2s, 1d, 0h(11/2)) model space using e(eff)(nu) =1.0 e follows the experimental values for the neutron rich Sn isotopes, but fails to reproduce the results presented here.
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| 10. |
- Hultquist, Gunnar, et al.
(författare)
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Hydrogen in chromium : Influence on the high-temperature oxidation kinetics in H2O, oxide-growth mechanisms, and scale adherence
- 2000
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Ingår i: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 54:02-jan, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of 1-mm thick chromium samples with 7 to < I wt, ppm hydrogen has been studied at 900 degrees C in a closed reaction chamber. The gases used were O-2, H2O, and gas mixtures of Oz; H2O at a total pressure of about 20 mbar. By means of oxygen labeling in two-stage oxidations, H2O followed by (H2O)-O-18, the position of oxide growth within the oxide scale was determined with secondary-ion mass spectrometry (SIMS). The results are consistent with visual observations and scanning electron microscopy (SEM), which shows flat oxides with good adherence when formed in H2O. When replacing O-2 out H2O in the atmosphere, the oxidation rate increases by a factor of two with an increase of oxide growth at both the inner and outer part of the oxide. An increased metal (cation) transport is observed when 5 wt. ppm hydrogen is present in the chromium metal prior to oxidation in both Oz and H2O. This is detrimental for the adherence of the oxide scale. The uptake of hydrogen in H2O exposure for 1600 min was measured to 1.5 wt. ppm. In exposures to O-2 + H2O mixtures, no H-2 is formed and no net water is consumed as long as O-2 is present. A plausible reaction scheme based on an experiment with (H2O)-O-18 is presented to explain this observation.
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| 11. |
- Hultquist, Gunnar, et al.
(författare)
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Self-repairing metal oxides
- 2001
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Ingår i: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 56:04-mar, s. 313-346
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of Cu, Zr, and alloys forming chromia, alumina, and zirconia was studied in a closed reaction chamber in O-2 gas near 20 mbar. Information on the position of oxide growth has been gained from the O-18/SIMS technique. Rates Of O-2 dissociation on metal oxides, Au, and Pt have been evaluated from measurements in labeled O-2. The experimental results indicate that hydrogen in the metal substrates induces increased metal-ion transport in internal oxide surfaces during oxidation, which leads to increased oxide growth at the oxide-gas interface. Experiments also show that oxides of rare-earth metals (REM) and Pt catalyze the dissociation Of O-2. An increased rate of O-2 dissociation can lead to increased transport of oxygen ions in the oxides and increased oxide growth at the substrate-oxide interface. A balanced transport of metal and oxygen ions in metal oxides that leads to oxide growth at both the metal-oxide and at the oxide-gas interface is found to be favorable for the formation of protective oxides with good adherence to the metal substrate. Depending on the original proporation of metal-to-oxygen ion transport in the oxide, an addition of hydrogen will increase or decrease the oxidation kinetics. In analogy, an addition of REM will increase or decrease the oxidation kinetics, depending on the original proportion of metal-to-oxygen ion transport.
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| 12. |
- Tveten, B., et al.
(författare)
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Hydrogen and yttria in chromium : Influence on the high-temperature oxidation kinetics in O-2, oxide-growth mechanisms and scale adherence
- 2001
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Ingår i: Oxidation of Metals. - 0030-770X .- 1573-4889. ; 55:04-mar, s. 279-289
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Tidskriftsartikel (refereegranskat)abstract
- The effects of hydrogen and Y2O3 on high-temperature oxidation of Cr in 20 mbar O-2 have been studied at 900 degreesC. Oxidation- and O-2-dissociation rates were determined from gas-phase measurements. Hydrogen in Cr leads to breakdown of the oxide scale. The oxide scale on Cr-1%Y2O3 charged with hydrogen for 4 hr (resulting in Cr-1%Y2O3 with approximately 10 ppm hydrogen) is adherent to the metal substrate. The oxidation rate is similar for Cr with less than or equal to1 ppm hydrogen and Cr-1%Y2O3 with less than or equal to1 ppm hydrogen, but significantly lower for 4-hr H-charged Cr-1%Y2O3.. The oxidation rate of Cr-5%Fe-1%Y2O3-25 ppm H is also lower than the oxidation rate of Cr-5%Fe-1%Y2O3-less than or equal to1 ppm? H. This indicates that unless hydrogen is present, there are virtually no effects of the addition of 1% Y2O3 to Cr. Using labeled oxygen, O-16,16(2) and O-18,18(2), was found that at 900 degreesC the dissociation rate of O-2 is higher on Y2O3 than on Cr2O3 It is suggested that the well-known improvement of the oxidation resistance of Cr as an effect of additions of Y or Y2O3 is related to an increase in the dissociation rate of O-2 and that there is a synergetic effect in combining Y2O3 and hydrogen.
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| 13. |
- Wadsater, Maria, et al.
(författare)
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Aligning Nanodiscs at the Air-Water Interface, a Neutron Reflectivity Study
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:24, s. 15065-15073
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Tidskriftsartikel (refereegranskat)abstract
- Nanodiscs are self-assembled nanostructures composed of a belt protein and a small patch of lipid bilayer, which can solubilize membrane proteins in a lipid bilayer environment. We present a method for the alignment of a well-defined two-dimensional layer of nanodiscs at the air-water interface by careful design of an insoluble surfactant monolayer at the surface. We used neutron reflectivity to demonstrate the feasibility of this approach and to elucidate the structure of the nanodisc layer. The proof of concept is hereby presented with the use of nanodiscs composed of a mixture of two different lipid (DMPC and DMPG) types to obtain a net overall negative charge of the nanodiscs. We find that the nanodisc layer has a thickness or 40.9 +/- 2.6 angstrom with a surface coverage of 66 +/- 4%. This layer is located about 15 angstrom below a cationic surfactant layer at the air water interface. The high level of organization within the nanodiscs layer is reflected by a low interfacial roughness (similar to 4.5 angstrom) found. The use of the nanodisc as a biomimetic model of the cell membrane allows for studies of single membrane proteins isolated in a confined lipid environment. The 2D alignment of nanodiscs could therefore enable studies of high-density layers containing membrane proteins that, in contrast to membrane proteins reconstituted in a continuous lipid bilayer, remain isolated front influences of neighboring membrane proteins within the layer.
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| 14. |
- Wallinder, D., et al.
(författare)
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Hydrogen in chromium : influence on corrosion potential and anodic dissolution in neutral NaCl solution
- 2001
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Ingår i: Corrosion Science. - 0010-938X .- 1879-0496. ; 43:7, s. 1267-1281
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Tidskriftsartikel (refereegranskat)abstract
- The influence of hydrogen charging, outgassing, pickling and passivation of mechanically polished chromium was investigated with respect to corrosion potential and anodic dissolution in 0.3 M NaCl solution. Secondary ion mass spectroscopy measurements were used to detect hydrogen after hydrogen charging by means of cathodic polarization. The results show that hydrogen in chromium decreases the corrosion potential and increases the anodic dissolution rate. Passivation in HNO3 and pickling in HNO3 + HF increases the corrosion potential, whereas no significant effect on the anodic dissolution could be observed, probably due to a hydrogen uptake in these surface treatments.
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