| 1. |
- Delafosse, C., et al.
(författare)
-
Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni-78 Region : A Hint from Lifetime Measurements
- 2018
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 121:19
-
Tidskriftsartikel (refereegranskat)abstract
- Lifetime measurements of excited states of the light N = 52 isotones Kr-88, Se-86, and Ge-84 have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2; 2(+)-> 0(+)) and B(E2; 4(+)-> 2(+)) were obtained for the first time for the hard-to-reach 84Ge. While the B(E2; 2(+)-> 0(+) ) values of Kr-88, Se-86 saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g(7/2), 1h(11/2)) space of an inert Ni-78 core, the value obtained for Ge-84 largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N less than or similar to 49, extend beyond N = 50. The onset of collectivity at Z = 32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector rho field in shell-structure evolution.
|
|
| 2. |
- Gjestvang, D., et al.
(författare)
-
Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments
- 2023
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 108:6
-
Tidskriftsartikel (refereegranskat)abstract
- The population of isomeric states in the prompt decay of fission fragments-so-called isomeric yield ratios (IYRs)-is known to be sensitive to the angular momentum J that the fragment emerged with, and may therefore contain valuable information on the mechanism behind the fission process. In this work, we investigate how changes in the fissioning system impact the measured IYRs of fission fragments to learn more about what parameters affect angular momentum generation. To enable this, a new technique for measuring IYRs is first demonstrated. It is based on the time of arrival of discrete gamma rays, and has the advantage that it enables the study of the IYR as a function of properties of the partner nucleus. This technique is used to extract the IYR of 134Te, strongly populated in actinide fission, from the three different fissioning systems: 232Th(n, f), 238U(n, f), at two different neutron energies, as well as 252Cf(sf). The impacts of changing the fissioning system, the compound nuclear excitation energy, the minimum J of the binary partner, and the number of neutrons emitted on the IYR of 134Te are determined. The decay code TALYS is used in combination with the fission simulation code FREYA to calculate the primary fragment angular momentum from the IYR. We find that the IYR of 134Te has a slope of 0.004 +/- 0.002 with increase in compound nucleus (CN) mass. When investigating the impact on the IYR of increased CN excitation energy, we find no change with an energy increase similar to the difference between thermal and fast fission. By varying the mass of the partner fragment emerging with 134Te, it is revealed that the IYR of 134Te is independent of the total amount of prompt neutrons emitted from the fragment pair. This indicates that neutrons carry minimal angular momentum away from the fission fragments. Comparisons with the FREYA+TALYS simulations reveal that the average angular momentum in 134Te following 238U(n, f) is 6.0 h over bar . This is not consistent with the value deduced from recent CGMF calculations. Finally, the IYR sensitivity to the angular momentum of the primary fragment is discussed. These results are not only important to help understanding the underlying mechanism in nuclear fission, but can also be used to constrain and benchmark fission models, and are relevant to the gamma -ray heating problem of reactors.
|
|
| 3. |
- Leyser, Diego, et al.
(författare)
-
Corrosion-fatigue of carbon steels in sweet and sour corrosion environments : Analysis of cyclic elastic and plastic strain effects on the electrochemical behavior by a transient corrosion current method
- 2017
-
Ingår i: NACE - International Corrosion Conference SeriesVolume 5, 2017, Pages 3564-3578Corrosion Conference and Expo 2017; New Orleans; United States; 26 March 2017 through 30 March 2017.. - : National Assoc. of Corrosion Engineers International. - 9781510840348 ; , s. 3564-3578
-
Konferensbidrag (refereegranskat)abstract
- The effects of cyclic stress and strain on corrosion-fatigue in sweet and sour corrosion were studied with an electrochemical approach. Cold-drawn and cold rolled carbon steel samples were mechanically cycled in a confined and CO2-saturated synthetic seawater solution, and their electrochemical response was acquired with a classic 3-electrode apparatus. The effect of elastic static stress was evaluated with the Linear Polarization Resistance (LPR) method. The effect of dynamic stresses, strain rate and plastic strain were evaluated by a potentiostatic method, at imposed steady-state Open Circuit Potential (OCP). Both methods show a linear dependency of the work electrode potential with respect to the applied stress. The latter method allowed the detection of an anodic contribution, proportional to the plastic deformation and to the strain rate. Using these findings, a time-domain model was built, in the form of a RLC circuit, associated to the electrochemical behavior. The calculations show a good agreement with the experimental results, and support the detected influences of stress, strain rate and plastic strain.
|
|
