1,541 research outputs found

    Low-lying GT(+) strength in Co-64 studied via the Ni-64(d,He-2)Co-64 reaction

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    The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios

    Hamiltonian Light-Front Field Theory: Recent Progress and Tantalizing Prospects

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    Fundamental theories, such as Quantum Electrodynamics (QED) and Quantum Chromodynamics (QCD) promise great predictive power addressing phenomena over vast scales from the microscopic to cosmic scales. However, new non-perturbative tools are required for physics to span from one scale to the next. I outline recent theoretical and computational progress to build these bridges and provide illustrative results for Hamiltonian Light Front Field Theory. One key area is our development of basis function approaches that cast the theory as a Hamiltonian matrix problem while preserving a maximal set of symmetries. Regulating the theory with an external field that can be removed to obtain the continuum limit offers additional possibilities as seen in an application to the anomalous magnetic moment of the electron. Recent progress capitalizes on algorithm and computer developments for setting up and solving very large sparse matrix eigenvalue problems. Matrices with dimensions of 20 billion basis states are now solved on leadership-class computers for their low-lying eigenstates and eigenfunctions.Comment: 8 pages with 2 figure

    In-beam fast-timing measurements in 103,105,107Cd

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    Fast-timing measurements were performed recently in the region of the medium-mass 103,105,107Cd isotopes, produced in fusion evaporation reactions. Emitted gamma-rays were detected by eight HPGe and five LaBr3:Ce detectors working in coincidence. Results on new and re-evaluated half-lives are discussed within a systematic of transition rates. The 7/21+7/2_1^+ states in 103,105,107Cd are interpreted as arising from a single-particle excitation. The half-life analysis of the 11/21‚ąí11/2_1^- states in 103,105,107Cd shows no change in the single-particle transition strength as a function of the neutron number

    Protocolo y mapa de diversidad funcional.

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    En este documento se exploran los patrones espaciales de la diversidad taxonómica y funcional de aves en ecosistemas alto andinos y humedales de Colombia y se discuten las consecuencias teóricas, de manejo y conservación del acoplamiento/desacoplamiento de ambas dimensiones de la biodiversidad. Este producto es elaborado por el Programa de Ciencias de la Diversidad en el marco del convenio 005 (13-014) entre el Instituto Humboldt y el Fondo Adaptación.BogotáSubdirección de Servicios Científicos y Proyectos Especiale

    Study of (n,xng) reactions on 238U

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    Prompt-gamma spectroscopy and time-of-flight techniques were used to measure (n,xn gamma) cross-sections on several nuclei of interest for nuclear reactors. Experiments were performed at the GELINA facility which provides a pulsed white neutron beam of maximum energy about 20 MeV. Preliminary results concerning 238U will be presented. This work was supported by PACEN/GEDEPEONand by the European Commission within the Sixth Framework Programme through I3-EFNUDAT (EURATOMcontract no. 036434) and NUDAME (Contract FP6-516487), and within the Seventh Framework Programme through EUFRAT (EURATOM contract no. FP7-211499) and through ANDES (EURATOM contract no. FP7-249671).JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

    Cross section measurements of 155,157Gd(n, ő≥) induced by thermal and epithermal neutrons

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    © SIF, Springer-Verlag GmbH Germany, part of Springer Nature 2019Neutron capture cross section measurements on 155Gd and 157Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n_TOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C6D6 liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for 155Gd and 157Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181 eV and 307 eV, respectively for 155Gd and 157Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2. 01 (28) × 10 - 4 and 2. 17 (41) × 10 - 4; average total radiative width of 106.8(14) meV and 101.1(20) meV and s-wave resonance spacing 1.6(2) eV and 4.8(5) eV for n + 155Gd and n + 157Gd systems, respectively.Peer reviewedFinal Accepted Versio

    Mapa de unidades evolutivas de aves en √°reas de p√°ramos y humedales.

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    Este producto es elaborado por el Programa de Gesti√≥n de la Informaci√≥n y el Conocimiento (GIC) en el marco del convenio 005 (13-014) entre el Instituto Humboldt y el Fondo Adaptaci√≥n, en este trabajo se cuantifica la diversidad taxon√≥mica y filogen√©tica de las aves presentes en p√°ramos y humedales. Adicionalmente, se eval√ļa la estructura filogen√©tica de estas comunidades para detectar √°reas significativamente altas o bajas en la filodiversidad que presentan. Finalmente se estiman la disimilitud evolutiva entre las comunidades, equivalente a una beta filodiversidad, con el fin de evidenciar la conectividad evolutiva de las comunidades en p√°ramos.Bogot√°Subdirecci√≥n de Servicios Cient√≠ficos y Proyectos Especiale

    JRC data for the Ti-48 standard

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    A measurement of the 48Ti(n,n’gamma)48Ti reaction was performed at the GELINA neutron source of EC-JRC-IRMM using the GAINS spectrometer with the purpose of establishing a new gamma-ray standard for neutron induced cross section measurements. A natural target was used and the gamma-production cross section was measured for 10 transitions in the neutron energy range 0-18 MeV. The lowest achieved uncertainty was 4.8%.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

    Time-of-flight and activation experiments on 147Pm and 171Tm for astrophysics

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    The neutron capture cross section of several key unstable isotopes acting as branching points in the s-process are crucial for stellar nucleosynthesis studies, but they are very challenging to measure due to the difficult production of sufficient sample material, the high activity of the resulting samples, and the actual (n,ő≥) measurement, for which high neutron fluxes and effective background rejection capabilities are required. As part of a new program to measure some of these important branching points, radioactive targets of 147Pm and 171Tm have been produced by irradiation of stable isotopes at the ILL high flux reactor. Neutron capture on 146Nd and 170Er at the reactor was followed by beta decay and the resulting matrix was purified via radiochemical separation at PSI. The radioactive targets have been used for time-of-flight measurements at the CERN n-TOF facility using the 19 and 185 m beam lines during 2014 and 2015. The capture cascades were detected using a set of four C6D6 scintillators, allowing to observe the associated neutron capture resonances. The results presented in this work are the first ever determination of the resonance capture cross section of 147Pm and 171Tm. Activation experiments on the same 147Pm and 171Tm targets with a high-intensity 30 keV quasi-Maxwellian flux of neutrons will be performed using the SARAF accelerator and the Liquid-Lithium Target (LiLiT) in order to extract the corresponding Maxwellian Average Cross Section (MACS). The status of these experiments and preliminary results will be presented and discussed as well

    New measurement of the 242Pu(n,ő≥) cross section at n-TOF-EAR1 for MOX fuels : Preliminary results in the RRR

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    The spent fuel of current nuclear reactors contains fissile plutonium isotopes that can be combined with 238U to make mixed oxide (MOX) fuel. In this way the Pu from spent fuel is used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. The use of MOX fuels in thermal and fast reactors requires accurate capture and fission cross sections. For the particular case of 242Pu, the previous neutron capture cross section measurements were made in the 70's, providing an uncertainty of about 35% in the keV region. In this context, the Nuclear Energy Agency recommends in its "High Priority Request List" and its report WPEC-26 that the capture cross section of 242Pu should be measured with an accuracy of at least 7-12% in the neutron energy range between 500 eV and 500 keV. This work presents a brief description of the measurement performed at n-TOF-EAR1, the data reduction process and the first ToF capture measurement on this isotope in the last 40 years, providing preliminary individual resonance parameters beyond the current energy limits in the evaluations, as well as a preliminary set of average resonance parameters
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