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The 237Np(n,f) cross sections have been measured at the n-TOF facility relative to the 235U and 238U fission cross sections. The n-TOF spallation neutron source at CERN is characterized by a high intensity flux, an excellent time resolution and an extensive neutron energy range (from eV to GeV). A fast ionization chamber was used as a fission fragment detector with efficiency better than 97%. Preliminary 237Np(n,f) cross sections have been deduced in the energy range from 20 keV to 10 MeV and are found in good agreement with data from literature. [ABSTRACT FROM AUTHOR]

Heavy elements with Z≥30 are made by neutron capture reactions during stellar He burning and presumably in supernovae. This contribution deals mainly with the slow neutron capture (s) process which is responsible for about one half of the abundances in the mass region between Fe and Bi. The slow time scale implies that the reaction path of this process involves mostly stable isotopes which can be studied in detail in laboratory experiments. The neutron time of flight (n_TOF) facility at CERN is a neutron spallation source, its white neutron energy spectrum ranges from thermal to several MeV, covering the full energy range of interest for nuclear astrophysics, in particular for measurements of the neutron capture cross section required in s-process nucleosynthesis. This contribution gives an overview on the astrophysical program made at n_TOF facility, the results and the implications will be considered. [ABSTRACT FROM AUTHOR]

Neutron induced fission cross sections of several isotopes have been measured at the CERN n_TOF spallation neutron facility. Between them some measurements involve isotopes (233U, 241Am, 243Am, 245Cm) relevant for applications to nuclear technologies. The n_TOF facility delivers neutrons with high instantaneous flux and in a wide energy range, from thermal up to 250 MeV. The experimental apparatus consists of an ionization chamber that discriminates fission fragments and α particles coming from natural radioactivity of the samples. All the measurements were performed referring to the standard cross section of 235U. [ABSTRACT FROM AUTHOR]

Neutron-induced fission cross-sections of minor actinides have been measured at the white neutron source n_TOF at CERN, Geneva. The studied isotopes include 233U, interesting for Th/U based nuclear fuel cycles, 241,243Am and 245Cm, relevant for transmutation and waste reduction studies in new generation fast reactors (Gen-IV) or Accelerator Driven Systems. The measurements take advantage of the unique features of the n_TOF facility, namely the wide energy range, the high instantaneous neutron flux and the low background. Results for the involved isotopes are reported from ∼30 meV to around 1 MeV neutron enegy. The measurements have been performed with a dedicated Fission Ionization Chamber (FIC), relative to the standard cross-section of the 235U fission reaction, measured simultaneously with the same detector. Results are here reported. [ABSTRACT FROM AUTHOR]

The neutron Time-of-Flight facility at CERN was built to measure the neutron capture and fission cross sections. A short description of the facility, the detectors and the data analysis techniques will be illustrated. A short review of the preliminary results on the fission cross sections is presented together with the implications in fundamental nuclear physics and in nuclear technologies. Future perspectives both for the experimental campaign and for the upgrade of the facility are discussed. [ABSTRACT FROM AUTHOR]

Nuclear astrophysics, advanced nuclear technology and nuclear structure physics present many cases that require neutron capture reaction data with high precision. In particular, refined data are needed for stellar nucleosynthesis, for nuclear waste transmutation studies, and for the design of generation IV reactors. The measurements take profit of the pulsed neutron beam of the n_TOF facility at CERN, which is generated by proton-induced spallation reactions on a massive lead target. The low repetition rate of the proton beam, the high instantaneous neutron flux, and the favourable background conditions in the experimental area make this facility unique for high resolution time-of-flight measurements of neutron induced reaction cross sections. The n_TOF collaboration is presently operating two different experimental set-ups. The first consists of two low-neutron sensitivity C6D6 detectors with the analysis relying on the Pulse Height Weighting technique. In addition, a Total Absorption Calorimeter, consisting of 40 BaF2 crystals covering the whole solid angle, was used. A review of several capture measurements with these detectors on selected stable and unstable samples will be presented. [ABSTRACT FROM AUTHOR]

The neutron Time-of-Flight facility at CERN has been used for a series of neutron capture and fission cross sections measurements. The facility, detectors and data analysis techniques are described, followed by a brief review of the capture results and of the preliminary results for selected fission cross sections. The problem of photon strength functions is discussed and preliminary first results are presented. All these subjects are discussed with respect to their implications in Nuclear Astrophysics. The last section is dedicated to the future perspectives concerning the next experimental campaign and the upgrade of the facility. [ABSTRACT FROM AUTHOR]

During the 2004 campaign, the n_TOF collaboration measured neutron fission cross sections for 233U, 241,243Am, 245Cm, as well as the fission standards 235,238U, using a sealed Fission Ionization Chamber (FIC). The setup included a total of 16 targets and 18 electrodes mounted together in a 50-cm length chamber, allowing the measurements of all isotopes at the same time, thus in the same experimental conditions. A brief description of the facility and of the detector setup will be presented followed by the preliminary results of the analysis of 235U, 233U, and 245Cm from thermal energies up to some tenths of MeV. [ABSTRACT FROM AUTHOR]

In the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos” monoenergetic neutron beams have been used in the energy range 7–11.5 MeV, produced via the 2H(d,n) reaction. The flux variation of the neutron beam is monitored by using a BF3 detector, while an investigation of the energy dependence of the neutron fluence is carried out via the multiple foil activation technique. The 232Th(n,2n)231Th and 241Am(n,2n)240Am as well as (n,2n), (n,p) and (n,α) reactions on natural Ge and Hf isotopes, have been investigated from threshold up to 11.5 MeV, by using the activation method. The cross section values have been determined relative to the 197Au(n,2n)196Au, 27Al(n,α)24Na and 93Nb(n,2n) reference reaction cross sections. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We measured the neutron capture cross section of 139La relative to 197Au in the energy range of 0.6 eV to 9 keV at n_TOF, the neutron time-of-flight facility at CERN. After a description of the experimental apparatus, we discuss data analysis procedures. The data were fitted using R-matrix formalism to extract resonance parameters which, in turn, were used to calculate average level spacings D0 = 268 ± 22 eV and D1 < 250 eV, and neutron strength functions S0 = (0.79 ± 0.03)×10-4 and S1 = (0.73 ± 0.05)×10-4 for s- and p-wave resonances. The data also were used to determine Maxwellian-averaged neutron capture cross sections which, in turn, were used to calculate the 139La abundance synthesized in a stellar model of the main component of the s process. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The neutron capture cross sections of 204Pb and 206Pb have been measured at the CERN n_TOF installation using the time of flight method with the pulse height weighting technique. In a preliminary analysis of 204Pb we have determined by first time the capture cross sections for two strong s-wave resonances below 2.5 keV, which seem to enhance the Maxwellian Averaged Cross Section at kT = 5 keV by about a factor of two with respect to the value assumed so far. In 206Pb we have determined capture cross sections for a large number (97) of resonances, which were not reported in the two previous capture measurements. We discuss preliminary implications of the new cross sections in the stellar nucleosynthesis of the Pb isotopes. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Accurate and reliable neutron capture cross section data for actinides are necessary for the proper design, safety regulation and precise performance assessment of transmutation devices such as Fast Critical Reactors or Accelerator Driven Systems. In particular, the neutron capture cross sections of 237Np, 240Pu and 243Am play a key role in the design and optimization of strategies for the Transmutation of Nuclear Waste. The listed cross sections have been measured in 2004 at n_TOF with a high accuracy due to a combination of features unique in the world: high instantaneous neutron fluence and excellent energy resolution of the n_TOF facility, innovative Data Acquisition System based on flash ADCs and the use of a high performance BaF2 Total Absorption Calorimeter as a detection device. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The use of a fuel cycle based on 232Th can substantially reduce the radiotoxicity of the produced nuclear waste since the lower atomic and mass number of thorium results in a strongly suppressed build-up of the higher actinides and especially americium and curium. The design and realization of nuclear power stations based on the use of thorium, either in a critical or subcritical system, require an accurate knowledge of the 232Th(n,γ) reaction cross section. We have measured the neutron capture cross section of 232Th at the recently constructed neutron time-of-flight facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. In the resolved resonance region, the resonance parameters have been extracted. In the unresolved resonance region, the neutron capture cross section is given as point-wise data. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The neutron Time of Flight (n_TOF) facility at CERN is a source of a wide-range (1 eV

The neutron capture cross sections for Zr isotopes have important implications in nuclear technologies as well in the field of nuclear astrophysics. The innovative features of the n_TOF CERN facility allowed for an accurate determination of the capture cross sections for these isotopes. The preliminary results of the measurements show capture-resonance strengths systematically smaller than in previously available data. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

A series of measurements of 237Np fission cross section have been performed at the CERN spallation neutron facility n_TOF which covers a wide energy range from 1 eV up to 250 MeV. A fast ionization chamber (FIC) was used as a fission fragment detector with registration efficiency of not less than 97 %. Particular attention was paid to correct the fission cross section with use of 235U standard. Total experimental uncertainties are determined to be at the level of 3%. Analysis of the experimental data in the restricted neutron energy from 5 eV up to 1 MeV showed a systematic deviation from evaluated data (ENDF/B-VI). This discrepancy amounts to up to a factor 3 for resolved resonances in the neutron energy range of 5 eV – 2 KeV, and is in good agreement with some previous experiments. A similar disagreement at the level of 6–7% was found for higher energies around the threshold (En = 300 keV–1 MeV). This energy range is essential for the transmutation of neptunium in ADS or fast reactors. It is concluded that an updated evaluation of nuclear data for 237Np is required. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The radioactive decay of 187Re → 187Os (t1/2 = 43 Gyr) is suited for dating the onset of heavy-element nucleosynthesis. The radiogenic contribution to the 187Os abundance is the difference between the natural abundance and the corresponding s-process component. This component can be obtained via the well-established σN systematics using the neighboring s-only isotope 186Os, provided the neutron-capture cross sections of both isotopes are known with sufficient accuracy. We report on a new set of experiments performed with a C6D6 detector array at the n_TOF neutron spallation facility of CERN. The capture cross sections of 186Os, 187Os, and 188Os have been measured in the neutron-energy range between 1 eV and 1 MeV, and Maxwellian-averaged cross sections were deduced for the relevant thermal energies from kT=5 keV to 100 keV. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Accurate and reliable neutron-capture cross-section data for actinides are necessary for the proper design, safety regulation, and precise performance assessment of transmutation devices such as Fast Critical Reactors or Accelerator Driven Systems. In particular, the neutron-capture cross sections of 237Np, 240Pu, and 243Am play a key role in the design and optimization of a strategy for the Nuclear Waste Transmutation. The listed cross sections have been measured in 2004 at n_TOF with a high accuracy due to a combination of features unique in the world: high instantaneous neutron fluence and excellent energy resolution of the n_TOF facility, innovative Data Acquisition System based on flash ADCs, and the use of a high-performance BaF2 Total Absorption Calorimeter as a detection device. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

All the stable lead isotopes and 209Bi have been recently measured at n_TOF (CERN) in the range from 1 eV up to 1 MeV, using an optimized experimental setup, A set of two homemade C6D6 detectors with carbon-fibre canning was designed to greatly reduce the sensitivity to scattered neutrons. Surrounding elements like the sample holder and the sample exchanger have been made also of carbon fibre. The pulse-height weighting technique has been used in order to determine the (n,γ) cross sections. Concerning this technique, special care has been taken in the treatment of several sources of error leading to a total systematic uncertainty of less than 3%. Results on the analysed 209Bi and 207Pb capture data and a comparison with previous experiments and evaluations are presented. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The neutron facility at the 5.5 MV Tandem T11/25 Accelerator of NCSR “Demokritos” will be presented. The facility can deliver monoenergetic neutron beams in the energy range 120–650 keV, 4–11.5 MeV and 16–20.5 MeV via the 7Li(p,n), 2H(d,n) and 3H(d,n) reactions, respectively. The corresponding beam energies obtained from the accelerator, are 1.92–2.37 MeV protons, 0.8–9.6 MeV deuterons and 0.8–3.7 MeV deuterons, for the three reactions, respectively. Experimental results for neutron energies up to 11.5 MeV will be presented for the 232Th(n,2n)231Th reaction. In context with the CERN n-TOF collaboration, the cross section of this reaction has been measured relative to the 56Fe(n,p)56Mn and 27Al(n,α)24Na reaction cross sections, by using the activation method. In addition to the experimental work, theoretical Statistical model calculations have also been performed using the computer code STAPRE/F. The results are being compared to the experimental data. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The accurate knowledge of the 151Sm(n,γ) cross section has important implications for the nuclear technologies as well as for fundamental studies. Due to its radioactivity, the only experimental data available on 151Sm were derived from a transmission measurement. Nowadays thanks to the innovative features of neutron time-of-flight facility (n_TOF), it was possible to measure 151Sm(n,γ) cross section in a wide energy range and with good accuracy. We present, here, the main experimental results together with the implications concerning the nuclear astrophysical part. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The capture cross section of the 139La has been measured relative to 197Au standard at n_TOF. We provide here a short description of the experimental apparatus and of the data analysis procedures. The extracted resonance parameters allow to calculate the fundamental nuclear quantities such as average spacing 1=0 = 268 ± 22 eV, 1=1 < 250 eV neutron strength functions S0 = (0.79 ± 0.03)×10-4, and S1 = (0.73 ± 0.05)×10-4 and the Maxwellian-averaged capture cross section (MACS). The MACS is particularly useful for the determination of the abundance synthesized by the main component of the s process. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]