321 research outputs found

    Measurement of the 242Pu(n,f) cross section at n_TOF

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    Knowledge of neutron cross sections of various plutonium isotopes and other minor actinides is crucial for the design of advanced nuclear systems. The 242Pu(n,f) cross sections were measured at the CERN n-TOF facility, taking advantage of the wide energy range (from thermal to GeV) and the high instantaneous flux of the neutron beam. In this work, preliminary results are presented along with a theoretical cross section calculation performed with the EMPIRE code. © Owned by the authors, published by EDP Sciences, 2014

    High precision measurement of the radiative capture cross section of 238U at the n-TOF CERN facility

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    The importance of improving the accuracy on the capture cross-section of 238U has been addressed by the Nuclear Energy Agency, since its uncertainty significantly affects the uncertainties of key design parameters for both fast and thermal nuclear reactors. Within the 7th framework programme ANDES of the European Commission three different measurements have been carried out with the aim of providing the 238U(n,ő≥) cross-section with an accuracy which varies from 1 to 5%, depending on the energy range. Hereby the final results of the measurement performed at the n TOF CERN facility in a wide energy range from 1 eV to 700 keV will be presented

    New pathway to bypass the 15O waiting point

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    We propose the sequential reaction process 15^{15}O(pp,ő≥)(ő≤+\gamma)(\beta^{+})16^{16}O as a new pathway to bypass of the 15^{15}O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 1010^{10} times higher than the 15^{15}O(pp,ő≤+\beta^{+})16^{16}O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound 16^{16}F low lying states, obtained using the H(15^{15}O,p)15^{15}O reaction. The large (p,ő≥)(ő≤+)(p,\gamma)(\beta^{+}) cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed.Comment: submitte

    Probing Nuclear forces beyond the drip-line using the mirror nuclei 16^{16}N and 16^{16}F

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    Radioactive beams of 14^{14}O and 15^{15}O were used to populate the resonant states 1/2+^+, 5/2+^+ and 0‚ąí,1‚ąí,2‚ąí0^-,1^-,2^- in the unbound 15^{15}F and 16^{16}F nuclei respectively by means of proton elastic scattering reactions in inverse kinematics. Based on their large proton spectroscopic factor values, the resonant states in 16^{16}F can be viewed as a core of 14^{14}O plus a proton in the 2s1/2_{1/2} or 1d5/2_{5/2} shell and a neutron in 1p1/2_{1/2}. Experimental energies were used to derive the strength of the 2s1/2_{1/2}-1p1/2_{1/2} and 1d5/2_{5/2}-1p1/2_{1/2} proton-neutron interactions. It is found that the former changes by 40% compared with the mirror nucleus 16^{16}N, and the second by 10%. This apparent symmetry breaking of the nuclear force between mirror nuclei finds explanation in the role of the large coupling to the continuum for the states built on an ‚Ąď=0\ell=0 proton configuration.Comment: 6 pages, 3 figures, 2 tables, accepted for publication as a regular article in Physical Review

    Development of a novel segmented mesh MicroMegas detector for neutron beam profiling

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    A novel MicroMegas detector based on microbulk technology with an embedded XY strip structure was developed, obtained by segmenting both the mesh and the anode in perpendicular directions. This results in a very low-mass device with good energy and spatial resolution capabilities. Such a detector is practically ‚Äútransparent‚ÄĚ to neutrons, being ideal for in-beam neutron measurements and can be used as a quasi-online neutron beam profiler at neutron time-of-flight facilities. A dedicated front end electronics and acquisition system has been developed and used. The first studies of this new detection system are presented and discussed

    Indirect study of 19Ne states near the 18F+p threshold

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    The early E < 511 keV gamma-ray emission from novae depends critically on the 18F(p,a)15O reaction. Unfortunately the reaction rate of the 18F(p,a)15O reaction is still largely uncertain due to the unknown strengths of low-lying proton resonances near the 18F+p threshold which play an important role in the nova temperature regime. We report here our last results concerning the study of the d(18F,p)19F(alpha)15N transfer reaction. We show in particular that these two low-lying resonances cannot be neglected. These results are then used to perform a careful study of the remaining uncertainties associated to the 18F(p,a)15O and 18F(p,g)19Ne reaction rates.Comment: 18 pages, 8 figures. Accepted in Nuclear Physics

    Ni-62(n,gamma) and Ni-63(n,gamma) cross sections measured at the n_TOF facility at CERN

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    The cross section of the Ni-62(n,gamma) reaction was measured with the time-of-flight technique at the neutron time-of-flight facility n_TOF at CERN. Capture kernels of 42 resonances were analyzed up to 200 keV neutron energy and Maxwellian averaged cross sections (MACS) from kT = 5-100 keV were calculated. With a total uncertainty of 4.5%, the stellar cross section is in excellent agreement with the the KADoNiS compilation at kT = 30 keV, while being systematically lower up to a factor of 1.6 at higher stellar temperatures. The cross section of the Ni-63(n,gamma) reaction was measured for the first time at n_TOF. We determined unresolved cross sections from 10 to 270 keV with a systematic uncertainty of 17%. These results provide fundamental constraints on s-process production of heavier species, especially the production of Cu in massive stars, which serve as the dominant source of Cu in the solar system.Peer reviewedFinal Accepted Versio
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