The effect of dead-time and pile-up in counting experiments may become a significant source of uncertainty if not properly taken into account. Although analytical solutions to this problem have been ...proposed for simple set-ups with one or two detectors, these are limited when it comes to arrays where time correlation between the detector modules is used, and also in situations of variable counting rates. In this paper we describe the dead-time and pile-up corrections applied to the n_TOF Total Absorption Calorimeter (TAC), a 4π γ-ray detector made of 40 BaF2 modules operating at the CERN n_TOF facility. Our method is based on the simulation of the complete signal detection and event reconstruction processes and can be applied as well in the case of rapidly varying counting rates. The method is discussed in detail and then we present its successful application to the particular case of the measurement of 238U(n, γ) reactions with the TAC detector.
The neutron sensitivity of the C6D6 detector setup used at n_TOF facility for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica of the entire ...n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a natC sample, showing an excellent agreement above 1keV. At lower energies, an additional component in the measured natC yield has been discovered, which prevents the use of natC data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross-section measurements.
Thin 33S samples for the study of the 33S(n,α)30Si cross-section at the n_TOF facility at CERN were made by thermal evaporation of 33S powder onto a dedicated substrate made of kapton covered with ...thin layers of copper, chromium and titanium. This method has provided for the first time bare sulfur samples a few centimeters in diameter. The samples have shown an excellent adherence with no mass loss after few years and no sublimation in vacuum at room temperature. The determination of the mass thickness of 33S has been performed by means of Rutherford backscattering spectrometry. The samples have been successfully tested under neutron irradiation.
The neutron sensitivity of the C sub(6)D sub(6) detector setup used at n_TOF facility for capture measurements has been studied by means of detailed GEANT4 simulations. A realistic software replica ...of the entire n_TOF experimental hall, including the neutron beam line, sample, detector supports and the walls of the experimental area has been implemented in the simulations. The simulations have been analyzed in the same manner as experimental data, in particular by applying the Pulse Height Weighting Technique. The simulations have been validated against a measurement of the neutron background performed with a super(nat)C sample, showing an excellent agreement above 1 keV. At lower energies, an additional component in the measured super(nat)C yield has been discovered, which prevents the use of super(nat)C data for neutron background estimates at neutron energies below a few hundred eV. The origin and time structure of the neutron background have been derived from the simulations. Examples of the neutron background for two different samples are demonstrating the important role of accurate simulations of the neutron background in capture cross-section measurements.
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The integral measurement of the
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C(n, p)
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B reaction was performed at the neutron time-of-flight facility n_TOF at CERN. The total number of
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B nuclei produced per neutron pulse of the n_TOF ...beam was determined using the activation technique in combination with a time-of-flight technique. The cross section is integrated over the n_TOF neutron energy spectrum from reaction threshold at 13.6MeV to 10GeV. Having been measured up to 1GeV on basis of the
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U(n, f ) reaction, the neutron energy spectrum above 200MeV has been re-evaluated due to the recent extension of the cross section reference for this particular reaction, which is otherwise considered a standard up to 200MeV. The results from the dedicated GEANT4 simulations have been used to evaluate the neutron flux from 1GeV up to 10GeV. The experimental results related to the
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C(n, p)
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B reaction are compared with the evaluated cross sections from major libraries and with the predictions of different GEANT4 models, which mostly underestimate the
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B production. On the contrary, a good reproduction of the integral cross section derived from measurements is obtained with TALYS-1.6 calculations, with optimized parameters.
The angular distribution of fragments emitted in neutron-induced fission of Th-232 was measured in the white spectrum neutron beam at the n_TOF facility at CERN. A reaction chamber based on Parallel ...Plate Avalanche Counters (PPAC) was used, where the detectors and the targets have been tilted 45 degrees with respect to the neutron beam direction in order to cover the full angular range of the fission fragments. A GEANT4 simulation has been developed to study the setup efficiency. The data analysis and the preliminary results obtained for the Th-232(n,f) between fission threshold and 100 MeV are presented here.
The (n, α) reaction in the radioactive {sup 59}Ni is of relevance in nuclear astrophysics as {sup 59}Ni can be considered as the first branching point in the astrophysical s-process. Its relevance in ...nuclear technology is especially related to material embrittlement in stainless steel. However, there is a discrepancy between available experimental data and the evaluated nuclear data files for this reaction. At the n{sub T}OF facility at CERN, a dedicated system based on sCVD diamond diodes was set up to measure the {sup 59}Ni(n, α){sup 56}Fe cross section. The results of this measurement, with special emphasis on the dominant resonance at 203 eV, are presented here.
We have used the 4π BaF2 gamma-ray detector array at the n_TOF neutron time-of-flight facility at CERN for an experiment in order to determine the spins of resonances of n +87Sr by measuring the ...gamma-ray spectra and multiplicity distributions. The first results are presented here. We have assigned the orbital momentum ℓ to all evaluated resonances on the basis of their neutron widths. Further we have assigned the spin J to 16 s-wave resonances on based the population of low-lying levels.
The 241Am(n,γ) cross sections have been measured at the n_TOF facility at CERN using C6D6 liquid scintillators and time of flight spectrometry. The results in the resolved resonance range bring new ...constraints to evaluations below 150 eV, and the energy upper limit can be extended from 150 eV to 320 eV. The analysis goes from thermal energy to 150 keV, and the unresolved resonance range cross section turns out to be larger than expected by evaluations or otherwise measured by previous works. The thermal cross section is found to be σth = 740 ± 74 barns, which is larger than expected by evaluations and most previous measurements.
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