792 research outputs found

    First measurement of the neutron-emission probability with a surrogate reaction in inverse kinematics at a heavy-ion storage ring

    No full text
    International audienceNeutron-induced reaction cross sections of short-lived nuclei are imperative to understand the origin of heavy elements in stellar nucleosynthesis and for societal applications, but their measurement is extremely complicated due to the radioactivity of the targets involved. One way of overcoming this issue is to combine surrogate reactions with the unique possibilities offered by heavy-ion storage rings. In this work, we describe the first surrogate-reaction experiment in inverse kinematics, which we successfully conducted at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, using the 208^{208}Pb(p,p') reaction as a surrogate for neutron capture on 207^{207}Pb. Thanks to the outstanding detection efficiencies possible at the ESR, we were able to measure for the first time the neutron-emission probability as a function of the excitation energy of 208^{208}Pb. We demonstrate the strong connection between this probability and the neutron-induced radiative capture cross section of 207^{207}Pb, and provide reliable results for this cross section at neutron energies for which no experimental data exist

    First measurement of the neutron-emission probability with a surrogate reaction in inverse kinematics at a heavy-ion storage ring

    No full text
    International audienceNeutron-induced reaction cross sections of short-lived nuclei are imperative to understand the origin of heavy elements in stellar nucleosynthesis and for societal applications, but their measurement is extremely complicated due to the radioactivity of the targets involved. One way of overcoming this issue is to combine surrogate reactions with the unique possibilities offered by heavy-ion storage rings. In this work, we describe the first surrogate-reaction experiment in inverse kinematics, which we successfully conducted at the Experimental Storage Ring (ESR) of the GSI/FAIR facility, using the 208^{208}Pb(p,p') reaction as a surrogate for neutron capture on 207^{207}Pb. Thanks to the outstanding detection efficiencies possible at the ESR, we were able to measure for the first time the neutron-emission probability as a function of the excitation energy of 208^{208}Pb. We demonstrate the strong connection between this probability and the neutron-induced radiative capture cross section of 207^{207}Pb, and provide reliable results for this cross section at neutron energies for which no experimental data exist

    179^{179}Ta(n, ő≥) cross-section measurement and the astrophysical origin of the 180^{180}Ta isotope

    Get PDF
    180m^{180m}Ta is nature\u27s rarest (quasi) stable isotope and its astrophysical origin is an open question. A possible production site of this isotope is the slow neutron capture process in asymptotic giant branch stars, where it can be produced via neutron capture reactions on unstable 179^{179}Ta. We report a new measurement of the 179^{179}Ta(n,ő≥) 180^{180}Ta cross section at thermal-neutron energies via the activation technique. Our results for the thermal and resonance-integral cross sections are 952¬Ī57 and 2013¬Ī148 b, respectively. The thermal cross section is in good agreement with the only previous measurement [Phys. Rev. C 60, 025802 (1999)], while the resonance integral is different by a factor of ‚Čą1.7. While neutron energies in this work are smaller than the energies in a stellar environment, our results may lead to improvements in theoretical predictions of the stellar cross section

    179Ta(n,ő≥) cross-section measurement and the astrophysical origin of the 180Ta isotope

    Get PDF
    Tantalum-180m is nature's rarest (quasi) stable isotope and its astrophysical origin is an open question. A possible production site of this isotope is the slow neutron capture process in Asymptotic Giant Branch stars, where it can be produced via neutron capture reactions on unstable 179^{179}Ta. We report a new measurement of the 179^{179}Ta(n,ő≥n,\gamma)180^{180}Ta cross section at thermal neutron energies via the activation technique. Our results for the thermal and resonance-integral cross-sections are 952 ¬Ī\pm 57 b and 2013 ¬Ī\pm 148 b, respectively. The thermal cross section is in good agreement with the only previous measurement (Phys. Rev C {\bf 60} 025802, 1999), while the resonance integral is different by a factor of ‚Čą\approx1.7. While neutron energies in this work are smaller than the energies in a stellar environment, our results may lead to improvements in theoretical predictions of the stellar cross section

    New detection systems for an enhanced sensitivity in key stellar (n,ő≥) measurements

    No full text
    Neutron capture cross-section measurements are fundamental in the study of astrophysical phenomena, such as the slow neutron capture (s-) process of nucleosynthesis operating in red-giant and massive stars. However, neutron capture measurements via the time-of-flight (TOF) technique on key s-process nuclei are often challenging. Difficulties arise from the limited mass (‚ąľmg) available and the high sample-related background in the case of the unstable s-process branching points. Measurements on neutron magic nuclei, that act as s-process bottlenecks, are affected by low (n,ő≥) cross sections and a dominant neutron scattering background. Overcoming these experimental challenges requires the combination of facilities with high instantaneous flux, such as n_TOFEAR2, with detection systems with an enhanced detection sensitivity and high counting rate capabilities. This contribution reviews some of the latest detector developments in detection systems for (n,ő≥) measurements at n_TOF, such as i-TED, an innovative detection system which exploits the Compton imaging technique to reduce the dominant neutron scattering background and s-TED, a highly segmented total energy detector intended for high flux facilities. The discussion will be illustrated with results of the first measurement of key the s-process branching-point reaction 79Se(n,ő≥).Title in Web of Science: New detection systems for an enhanced sensitivity in key stellar (n,gamma) measurements</p

    Diverse mechanisms in proton knockout reactions from the Borromean nucleus 17Ne

    Get PDF
    Nucleon knockout experiments using beryllium or carbon targets reveal a strong dependence of the quenching factors, i.e., the ratio (R s) of theoretical to the experimental spectroscopic factors (C 2S), on the proton-neutron asymmetry in the nucleus under study. However, this dependence is greatly reduced when a hydrogen target is used. To understand this phenomenon, exclusive 1H (17Ne , 2p16F) and inclusive 12C(17Ne,2p16F)X , 12C (17Ne , 16F) X as well as 1H (17Ne , 16F) X (X-denotes undetected reaction products) reactions with 16F in the ground and excited states were analysed. The longitudinal momentum distribution of 16F and the correlations between the detached protons were studied. In the case of the carbon target, there is a significant deviation from the predictions of the eikonal model. The eikonal approximation was used to extract spectroscopic factor values C 2S . The experimental C 2S value obtained with C target is markedly lower than that for H target. This is interpreted as rescattering due to simultaneous nucleon knockout from both reaction partners, 17Ne and 12C

    High resolution

    No full text
    Neutron capture cross section measurements of isotopes close to s-process branching-points are of fundamental importance for the understanding of this nucleosynthesis mechanism through which about 50% of the elements heavier than iron are produced. We present in this contribution the results corresponding to the high resolution measurement, for first time ever, of the 80Se(n, ő≥) cross section, in which 98 resonances never measured before have been reported. As a consequence, ten times more precise values for the MACS have been obtained compared to previous accepted value adopted in the astrophysical KADoNiS data base

    Measurement of the 77Se(n,ő≥)^{77}Se ( n , ő≥ ) cross section up to 200 keV at the n_TOF facility at CERN

    Get PDF
    The 77Se(n,ő≥)^{77}Se ( n , ő≥ ) reaction is of importance for 77Se^{77}Se abundance during the slow neutron capture process in massive stars. We have performed a new measurement of the 77Se^{77}Se radiative neutron capture cross section at the Neutron Time-of-Flight facility at CERN. Resonance capture kernels were derived up to 51 keV and cross sections up to 200 keV. Maxwellian-averaged cross sections were calculated for stellar temperatures between kT=5¬†keVkT=5 \space keV and kT=100¬†keVkT=100\space keV, with uncertainties between 4.2% and 5.7%. Our results lead to substantial decreases of 14% and 19% in 77Se^{77}Se abundances produced through the slow neutron capture process in selected stellar models of 15M‚äô15M‚äô and 2M‚äô2M‚äô, respectively, compared to using previous recommendation of the cross section

    Measurement of the

    No full text
    The neutron capture cross section of 241Am is an important quantity for nuclear energy production and fuel cycle scenarios. Several measurements have been performed in recent years with the aim to reduce existing uncertainties in evaluated data. Two previous measurements, performed at the 185 m flight-path station EAR1 of the neutron time-of-flight facility n_TOF at CERN, have permitted to substantially extend the resolved resonance region, but suffered in the near-thermal energy range from the unfavorable signal-to-background ratio resulting from the combination of the high radioactivity of 241Am and the rather low thermal neutron flux. The here presented 241Am(n,ő≥) measurement, performed with C6D6 liquid scintillator gamma detectors at the 20 m flight-path station EAR2 of the n_TOF facility, took advantage of the much higher neutron flux. The current status of the analysis of the data, focussed on the low-energy region, will be described here

    Compton imaging for enhanced sensitivity (n,ő≥) cross section TOF experiments: Status and prospects

    No full text
    Radiative neutron-capture cross sections are of pivotal importance in many fields such as nucle-osynthesis studies or innovative reactor technologies. A large number of isotopes have been measured with high accuracy, but there are still a large number of relevant isotopes whose cross sections could not be experimentally determined yet, at least with sufficient accuracy and completeness, owing to limitations in detection techniques, sample production methods or in the facilities themselves. In the context of the HYMNS (High-sensitivitY Measurements of key stellar Nucleo-Synthesis reactions) project over the last six years we have developed a novel detection technique aimed at background suppression in radiative neutron-capture time-of-flight measurements. This new technique utilizes a complex detection set-up based on position-sensitive radiation-detectors deployed in a Compton-camera array configuration. The latter enables to implement gamma-ray imaging techniques, which help to disentangle true capture events arising from the sample under study and contaminant background events from the surroundings. A summary on the main developments is given in this contribution together with an update on recent experiments at CERN n_TOF and an outlook on future steps
    • ‚Ķ
    corecore