555 research outputs found

    Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions

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    The Trojan Horse method is a powerful indirect technique that provides information to determine astrophysical factors for binary rearrangement processes x+Ab+Bx + A \to b + B at astrophysically relevant energies by measuring the cross section for the Trojan Horse reaction a+Ay+b+Ba + A \to y+ b + B in quasi-free kinematics. We present the theory of the Trojan Horse method for resonant binary subreactions based on the half-off-energy-shell R matrix approach which takes into account the off-energy-shell effects and initial and final state interactions.Comment: 6 pages and 1 figur

    Silicon detectors for the n-TOF neutron beams monitoring

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    During 2014 the second experimental area EAR2 was completed at the n-TOF neutron beam facility at CERN. As the neutrons are produced via spallation, by means of a high-intensity 20 GeV pulsed proton beam impinging on a thick target, the resulting neutron beam covers an enormous energy range, from thermal to several GeV. In this paper we describe two beam diagnostic devices, designed and built at INFN-LNS, both exploiting silicon detectors coupled with neutron converter foils containing 6Li. The first one is based on four silicon pads and allows to monitor the neutron beam flux as a function of the neutron energy. The second one, based on position sensitive silicon detectors, is intended for the reconstruction of the beam profile, again as a function of the neutron energy. Several electronic setups have been explored in order to overcome the issues related to the gamma flash, namely a huge pulse present at the start of each neutron bunch which may blind the detectors for some time. The two devices have been characterized with radioactive sources at INFN-LNS and then tested at n-TOF. The wide energy and intensity range they proved capable of sustaining, made them quite attractive and suitable to be used in both EAR1 and EAR2 n-TOF experimental areas, where they became immediately operational.Comment: submitted to Review of Scientific Instrument

    Solving the large discrepancy between inclusive and exclusive measurements of the 8Li+4He11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n reaction cross section at astrophysical energies

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    A solution of the large discrepancy existing between inclusive and exclusive measurements of the 8Li+4He11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n reaction cross section at Ecm<3E_{cm} <3 MeV is evaluated. This problem has profound astrophysical relevance for this reaction is of great interest in Big-Bang and r-process nucleosynthesis. By means of a novel technique, a comprehensive study of all existing 8Li+4He11B+n{}^8{\rm Li}+{}^4{\rm He}\to{}^{11}{\rm B}+n cross section data is carried out, setting up a consistent picture in which all the inclusive measurements provide the reliable value of the cross section. New unambiguous signatures of the strong branch pattern non-uniformities, near the threshold of higher 11B{}^{11}{\rm B} excited levels, are presented and their possible origin, in terms of the cluster structure of the involved excited states of 11B{}^{11}{\rm B} and 12B{}^{12}{\rm B} nuclei, is discussed.Comment: 5 pages, 4 figures, 1 tabl

    Pulse shape discrimination of charged particles with a silicon strip detector

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    Abstract A simple and effective pulse shape discrimination technique is applied to a silicon strip detector array. Excellent charge identification from H up to the Ni projectile has been obtained and isotope separation up to N has also been observed. The method we systematically studied is essentially based on a suitable setting of the constant fraction discriminators, and its main advantage is that no additional electronic modules are needed compared to the ones used in the standard TOF technique

    Radiation correction to astrophysical fusion reactions and the electron screening problem

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    We discuss the effect of electromagnetic environment on laboratory measurements of the nuclear fusion reactions of astrophysical interest. The radiation field is eliminated using the path integral formalism in order to obtain the influence functional, which we evaluate in the semi-classical approximation. We show that enhancement of the tunneling probability due to the radiation correction is extremely small and does not resolve the longstanding problem that the observed electron screening effect is significantly larger than theoretical predictions.Comment: 9 pages, 1 eps figure

    Breakup and n -transfer effects on the fusion reactions Li 6,7 + Sn 120,119 around the Coulomb barrier

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    This paper presents values of complete fusion cross sections deduced from activation measurements for the reactions Li6+Sn120 and Li7+Sn119, and for a projectile energy range from 17.5 to 28 MeV in the center-of-mass system. A new deconvolution analysis technique is used to link the basic activation data to the actual fusion excitation function. The complete fusion cross sections above the barrier are suppressed by about 70% and 85% with respect to the universal fusion function, used as a standard reference, in the Li6 and Li7 induced reactions, respectively. From a comparison of the excitation functions of the two systems at energies below the barrier, no significant differences can be observed, despite the two systems have different n-transfer Q values. This observation is supported by the results of coupled reaction channels (CRC) calculations

    Fusion rate enhancement due to energy spread of colliding nuclei

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    Experimental results for sub-barrier nuclear fusion reactions show cross section enhancements with respect to bare nuclei which are generally larger than those expected according to electron screening calculations. We point out that energy spread of target or projectile nuclei is a mechanism which generally provides fusion enhancement. We present a general formula for calculating the enhancement factor and we provide quantitative estimate for effects due to thermal motion, vibrations inside atomic, molecular or crystal system, and due to finite beam energy width. All these effects are marginal at the energies which are presently measurable, however they have to be considered in future experiments at still lower energies. This study allows to exclude several effects as possible explanation of the observed anomalous fusion enhancements, which remain a mistery.Comment: 17 pages with 3 ps figure included. Revtex styl
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