Refine
Year of publication
Document Type
- Article (33)
- Conference Proceeding (1)
- Doctoral Thesis (1)
Has Fulltext
- yes (35)
Is part of the Bibliography
- no (35)
Keywords
Institute
- Physik (34)
- ELEMENTS (11)
- Helmholtz International Center for FAIR (1)
We measured the neutron capture cross sections of 69Ga and 71Ga for a quasi-stellar spectrum at kBT = 25 keV and a spectrum with a peak energy at 90 keV by the activation technique at the Joint Research Centre (JRC) in Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction 7Li(p,n). The produced activity was measured via the γ emission of the product nuclei by high-purity germanium detectors. We present preliminary results.
The production of 77,79,85,85mKr and 77Br via the reaction Se(a, x) was investigated between Ea = 11 and 15 MeV using the activation technique. The irradiation of natural selenium targets on aluminum backings was conducted at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Germany. The spectroscopic analysis of the reaction products was performed using a high-purity germanium detector located at PTB and a low energy photon spectrometer detector at the Goethe University Frankfurt, Germany. Thicktarget yields were determined. The corresponding energy-dependent production cross sections of 77,79,85,85mKr and 77Br were calculated from the thicktarget yields. Good agreement between experimental data and theoretical predictions using the TALYS-1.6 code was found.
Im Rahmen dieser Arbeit wurden astrophysikalisch relevante, kernphysikalische Raten, die zum Verständnis der beobachteten Häufigkeit des langlebigen Isotopes 60Fe wichtig sind, am GSI Helmholtzzentrum für Schwerionenforschung GmbH und am Forschungsreaktor TRIGA in Mainz gemessen.
Zunächst wurde der Coulombaufbruch von 59Fe und 60Fe am GSI Helmholtzzentrum für Schwerionenforschung GmbH untersucht. Zur Produktion der radioaktiven Strahlen wurde ein 64Ni-Primärstrahl auf ein Spallationstarget geleitet. Im Fragmentseparator wurden die Isotope nach deren magnetischen Steifigkeit separiert und nur die gewünschte Spezies im LAND/R3B-Aufbau untersucht. Die Bestimmung von Impuls und Ladung der eingehenden Ionen erlaubte eine individuelle Identifikation. Der Coulombaufbruchwirkungsquerschnitt wurde mit einer Bleiprobe bestimmt. Die verschiedenen Untergrundkomponenten ergaben sich aus einer begleitenden Leermessung, sowie einer Messung mit einer Kohlenstoffprobe. Der Wirkungsquerschnitt der Reaktion Pb(60Fe,n+59Fe)Pb bei (530±5) MeV/u wurde zu σ(60Fe,n+59Fe) COULEX = (298±11stat±31syst) mb (0.1) bestimmt und für die Reaktion Pb(59Fe,n+58Fe)Pb ergab sich σ(59Fe,n+58Fe) COULEX = (410±11stat±41syst) mb. (0.2)
Außerdem konnten für beide einkommenden Strahlsorten die Wahrscheinlichkeiten für die Produktion von zwei Neutronen bestimmt werden.
Anschließend wurde der Neutroneneinfangsquerschnitt von 60Fe bei kT = 25,3 meV am Forschungsreaktor TRIGA in Mainz bestimmt. Hierfür wurde eine 60Fe Probe zunächst anhand des Anstieges der Aktivität der 60Co-Tochterkerne charakterisiert und anschließend im Reaktor bestrahlt. Die frisch erzeugte Aktivität des 61Fe wurde mit einem HPGe-Detektor nachgewiesen. Mit Hilfe der Cadmiumdifferenzmethode konnte daraus erstmals der thermische Neutroneneinfangsquerschnitt von 60Fe zu σ60Fe(n,γ) th = 0,22±0,02stat±0,02syst b. (0.3) bestimmt werden. Für das Resonanzintegral ergab sich die obere Schranke von I 60Fe(n,γ) res = 0,61 b. (0.4)
We discuss the possibility to build a neutron target for nuclear reaction studies in inverse kinematics utilizing a storage ring and radioactive ion beams. The proposed neutron target is a specially designed spallation target surrounded by a large moderator of heavy water (D2O). We present the resulting neutron spectra and their properties as a target. We discuss possible realizations at different experimental facilities.
The huge neutron fluxes offer the possibility to use research reactors to produce isotopes of interest, which can be investigated afterwards. An example is the half-lives of long-lived isotopes like 129I. A direct usage of reactor neutrons in the astrophysical energy regime is only possible, if the corresponding ions are not at rest in the laboratory frame. The combination of an ion storage ring with a reactor and a neutron guide could open the path to direct measurements of neutron-induced cross sections on short-lived radioactive isotopes in the astrophysically interesting energy regime.
New neutron cross section measurements of minor actinides have been performed recently in order to reduce the uncertainties in the evaluated data, which is important for the design of advanced nuclear reactors and, in particular, for determining their performance in the transmutation of nuclear waste. We have measured the 241Am(n,γ) cross section at the n_TOF facility between 0.2 eV and 10 keV with a BaF2 Total Absorption Calorimeter, and the analysis of the measurement has been recently concluded. Our results are in reasonable agreement below 20 eV with the ones published by C. Lampoudis et al. in 2013, who reported a 22% larger capture cross section up to 110 eV compared to experimental and evaluated data published before. Our results also indicate that the 241Am(n,γ) cross section is underestimated in the present evaluated libraries between 20 eV and 2 keV by 25%, on average, and up to 35% for certain evaluations and energy ranges.
Neutron-induced reaction cross sections are important for a wide variety of research fields ranging from the study of nuclear level densities, nucleosynthesis to applications of nuclear technology like design, and criticality and safety assessment of existing and future nuclear reactors, radiation dosimetry, medical applications, nuclear waste transmutation, accelerator-driven systems and fuel cycle investigations. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. CERN’s neutron time-of-flight facility n_TOF has produced a considerable amount of experimental data since it has become fully operational with the start of its scientific measurement programme in 2001. While for a long period a single measurement station (EAR1) located at 185 m from the neutron production target was available, the construction of a second beam line at 20 m (EAR2) in 2014 has substantially increased the measurement capabilities of the facility. An outline of the experimental nuclear data activities at n_TOF will be presented.
The 33S(n,α)30Si cross section measurement, using 10B(n,α) as reference, at the n_TOF Experimental Area 2 (EAR2) facility at CERN is presented. Data from 0.01 eV to 100 keV are provided and, for the first time, the cross section is measured in the range from 0.01 eV to 10 keV. These data may be used for a future evaluation of the cross section because present evaluations exhibit large discrepancies. The 33S(n,α)30Si reaction is of interest in medical physics because of its possible use as a cooperative target to boron in Neutron Capture Therapy (NCT).
The Cosmological Lithium Problem refers to the large discrepancy between the abundance of primordial 7Li predicted by the standard theory of Big Bang Nucleosynthesis and the value inferred from the so-called “Spite plateau” in halo stars. A possible explanation for this longstanding puzzle in Nuclear Astrophysics is related to the incorrect estimation of the destruction rate of 7Be, which is responsible for the production of 95% of primordial Lithium. While charged-particle induced reactions have mostly been ruled out, data on the 7Be(n,α) and 7Be(n,p) reactions are scarce or completely missing, so that a large uncertainty still affects the abundance of 7Li predicted by the standard theory of Big Bang Nucleosynthesis. Both reactions have been measured at the n_TOF facility at CERN, providing for the first time data in a wide neutron energy range.
High precision measurement of the radiative capture cross section of 238U at the n_TOF CERN facility
(2017)
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,γ) 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.
