| 1. |
- Girard-Alcindor, V., et al.
(författare)
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New narrow resonances observed in the unbound nucleus F 15
- 2022
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Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 105:5
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the unbound F15 nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O14 beam impinging on a CH2 target. The analysis of H1(O14,p)O14 and H1(O14,2p)N13 reactions allowed the confirmation of the previously observed narrow 1/2- resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2- and 3/2- resonances. The newly observed levels decay by 1p emission to the ground of O14, and by sequential 2p emission to the ground state of N13 via the 1- resonance of O14. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2- and 3/2- resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function H1(O14,p)O14 and resonance spectrum in F15 are well reproduced in the unified framework of the GSM.
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| 2. |
- Ciemala, M., et al.
(författare)
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Testing ab initio nuclear structure in neutron-rich nuclei : Lifetime measurements of second 2(+) state in C-16 and O-20
- 2020
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Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 101:2
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Tidskriftsartikel (refereegranskat)abstract
- To test the predictive power of ab initio nuclear structure theory, the lifetime of the second 2(+) state in neutron-rich O-20, tau(2(2)(+)) = 150(-30)(+80) fs, and an estimate for the lifetime of the second 2(+) state in C-16 have been obtained for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds of femtoseconds range by analyzing the Doppler-shifted gamma-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction O-18 (7.0 MeV/u) + Ta-181. The requested sensitivity could only be reached owing to the excellent performances of the Advanced gamma-Tracking Array AGATA, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two- and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for O-20 and with the no-core shell model for C-16. The present measurement shows the power of electromagnetic observables, determined with high-precision gamma spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetime measurements in unexplored regions of the nuclear chart, including r-process nuclei, when intense beams, produced by Isotope Separation On-Line (ISOL) techniques, become available.
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| 3. |
- Gjestvang, D., et al.
(författare)
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Examination of how properties of a fissioning system impact isomeric yield ratios of the fragments
- 2023
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 108:6
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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.
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| 4. |
- Qi, L., et al.
(författare)
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Potential of prompt γ -ray emission studies in fast-neutron induced fission : a first step
- 2020
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 56:3
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Tidskriftsartikel (refereegranskat)abstract
- Prompt γ-ray spectra emitted in fast-neutron induced fission of 239Pu have been recently measured by using the LICORNE directional neutron source at En = 1.8 MeV. The results are used in parallel with the measurements of fast-neutron induced fission of 238U and spontaneous fission of 252Cf to assess the potential of such reactions and observables, in contributing to the understanding of fission. The γ-ray spectra were measured and analyzed under similar conditions, allowing a consistent and robust comparison between the three systems. They are further compared to Monte–Carlo simulations based on two widely-used semi-empirical codes, FREYA and GEF. Differences in the low and high energy portions of the spectrum are interpreted based on simple arguments involving nuclear structure and evaporation effects. The significance and potential of experimental campaigns of this kind, as well as current limitations, are highlighted, together with straightforward but mandatory extensions.
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