arXiv subjects

D. Ramos

Publications and source records attributed to D. Ramos.

44 records · Page 3Linked to original sources

arXiv2020

Simultaneous determination of neutron-induced fission and radiative-capture cross sections from decay probabilities obtained with a surrogate reaction

Reliable neutron-induced reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative-capture cross sections of 239Pu in a consistent manner from a single measurement. This was achieved by combining simultaneously-measured fission and gamma-emission probabilities for the 240Pu(4He,4He') surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected gamma-ray transitions, we measure the gamma-emission probability. This enlarges the applicability of the surrogate-reaction method.

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arXiv2020

Scission configuration of $^{239}$U from yields and kinetic information of fission fragments

The simultaneous measurement of the isotopic fission-fragment yields and fission-fragment velocities of $^{239}$U has been performed for the first time. The $^{239}$U fissioning system was produced in one-neutron transfer reactions between a $^{238}$U beam at 5.88 MeV/nucleon and a $^{9}$Be target. The combination of inverse kinematics at low energy and the use of the VAMOS++ spectrometer at the GANIL facility allows the isotopic identification of the full fission-fragment distribution and their velocity in the reference frame of the fissioning system. The proton and neutron content of the fragments at scission, their total kinetic and total excitation energy, as well as the neutron multiplicity were determined. Information from the scission point configuration is obtained from these observables and the correlation between them. The role of the octupole-deformed proton and neutron shells in the fission-fragment production is discussed.

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arXiv2019

First direct measurement of isotopic fission-fragment yields of $^{239}$U

A direct and complete measurement of isotopic fission-fragment yields of $^{239}$U has been performed for the first time. The $^{239}$U fissioning system was produced with an average excitation energy of 8.3 MeV in one-neutron transfer reactions between a $^{238}$U beam and a $^{9}$Be target at Coulomb barrier energies. The fission fragments were detected and isotopically identified using the VAMOS++ spectrometer at the GANIL facility. This measurement allows to directly evaluate the fission models at excitation energies of fast neutrons, relevant for next-generation nuclear reactors. The present data, in agreement with model calculations, do not support the recently reported anomaly in the fission-fragment yields of $^{239}$U and confirm the persistence of spherical shell effects in the Sn region at excitation energies exceeding the fission barrier by few MeV.

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arXiv2017

High Precision Measurement of the $^{19}$Ne Half-life using real-time digital acquisition

The half-life of $^{19}$Ne has been measured using a real-time digital multiparametric acquisition system providing an accurate time-stamp and relevant information on the detectors signals for each decay event. An exhaustive offline analysis of the data gave unique access to experimental effects potentially biasing the measurement. After establishing the influence factors impacting the measurement such as after-pulses, pile-up, gain and base line fluctuations, their effects were accurately estimated and the event selection optimized. The resulting half-life, $17.2569\pm0.0019_{(stat)}\pm0.0009_{(syst)}$~s, is the most precise up to now for $^{19}$Ne. It is found in agreement with two recent precise measurements and not consistent with the most recent one [L.J. Broussard {\it et al.}, Phys. Rev. Lett. {\bf112}, 212301 (2014)] by 3.0 standard deviations. The full potential of the technique for nuclei with half-lives of a few seconds is discussed.

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arXiv2017

Cold Powering

Chapter 6 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC.

physics.acc-ph↗

arXiv2017

11 T Dipole for the Dispersion Suppressor Collimators

Chapter 11 in High-Luminosity Large Hadron Collider (HL-LHC) : Preliminary Design Report. The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC.

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arXiv2015

Characterization of the scission point from fission-fragment velocities

The isotopic-yield distributions and kinematic properties of fragments produced in transfer-induced fission of 240Pu and fusion-induced fission of 250Cf, with 9 MeV and 45 MeV of excitation energy respectively, were measured in inverse kinematics with the spectrometer VAMOS. The kinematic properties of identified fission fragments allow to derive properties of the scission configuration such as the distance between fragments, the total kinetic energy, the neutron multiplicity, the total excitation energy, and, for the first time, the proton- and neutron-number sharing during the emergence of the fragments. These properties of the scission point are studied as functions of the fragment atomic number. The correlation between these observables, gathered in one single experiment and for two different fissioning systems at different excitation energies, give valuable information for the understanding and modeling of the fission process.

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arXiv2013

Transfer reactions in inverse kinematics, an experimental approach for fission investigations

Inelastic and multi-nucleon transfer reactions between a $^{238}$U beam, accelerated at 6.14 MeV/u, and a $^{12}$C target were used for the production of neutron-rich, fissioning systems from U to Cm. A Si telescope, devoted to the detection of the target-like nuclei, provided a characterization of the fissioning systems in atomic and mass numbers, as well as in excitation energy. Cross-sections, angular and excitation-energy distributions were measured for the inelastic and transfer channels. Possible excitations of the target-like nuclei were experimentally investigated for the first time, by means of g -ray measurements. The decays from the first excited states of $^{12}$C, $^{11}$B and $^{10}$Be were observed with probabilities of 0.12 - 0.14, while no evidence for the population of higher-lying states was found. Moreover, the fission probabilities of $^{238}$U, $^{239}$Np and $^{240,241,242}$Pu and $^{244}$Cm were determined as a function of the excitation energy.

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