At the neutron time-of-flight facility n_TOF at CERN a new vertical beam line was constructed in 2014, in order to extend the experimental possibilities at this facility to an even wider range of ...challenging cross-section measurements of interest in astrophysics, nuclear technology and medical physics. The design of the beam line and the experimental hall was based on FLUKA Monte Carlo simulations, aiming at maximizing the neutron flux, reducing the beam halo and minimizing the background from neutrons interacting with the collimator or back-scattered in the beam dump.
The present paper gives an overview on the design of the beam line and the relevant elements and provides an outlook on the expected performance regarding the neutron beam intensity, shape and energy resolution, as well as the neutron and photon backgrounds.
For a consistent CFD substantiation of the recombiner performance, a detailed mechanism of hydrogen and oxygen recombination is used. The detailed mechanism of chemical kinetics (multi-step ...recombination reaction) makes it possible to claim universality, both in the numerical justification of the recombiner performance and in the justification of the flameless recombination threshold and makes it possible to justify the method for optimizing the recombiner to improve its characteristics. The models developed based on this approach were applied to both flat and cylindrical catalytic elements, which are used in FR and RVK recombiners, respectively. As part of the numerical studies, the detailed recombination mechanism was verified, namely the temperature distribution along the catalytic elements was compared and the performance of catalytic elements was compared as well. Good agreement was obtained between the calculated and experimental data. The approach considers not only the mechanism of surface recombination of hydrogen and oxygen on platinum, but also the mechanism of recombination in the gas phase. This makes it possible to calculate the onset of intense combustion outside the catalytic plates, which is a sign of volumetric ignition of the hydrogen-air environment. The concentrations at which such ignition is possible were obtained at different contents of water vapor in the medium. Thus, the proposed approach and the created models make it possible to fully describe the performance of recombiners of distinct designs without the use of additional experimental data, which is extremely necessary when justifying the hydrogen explosion safety of nuclear power plants.
Abstract
Neutron capture reaction cross sections on
$$^{74}$$
74
Ge are of importance to determine
$$^{74}$$
74
Ge production during the astrophysical slow neutron capture process. We present new ...resonance data on
$$^{74}$$
74
Ge(
$$n,\gamma $$
n
,
γ
) reactions below 70 keV neutron energy. We calculate Maxwellian averaged cross sections, combining our data below 70 keV with evaluated cross sections at higher neutron energies. Our stellar cross sections are in agreement with a previous activation measurement performed at Forschungszentrum Karlsruhe by Marganiec et al., once their data has been re-normalised to account for an update in the reference cross section used in that experiment.
.
A new high flux experimental area has recently become operational at the n_TOF facility at CERN. This new measuring station, n_TOF-EAR2, is placed at the end of a vertical beam line at a distance ...of approximately 20m from the spallation target. The characterization of the neutron beam, in terms of flux, spatial profile and resolution function, is of crucial importance for the feasibility study and data analysis of all measurements to be performed in the new area. In this paper, the measurement of the neutron flux, performed with different solid-state and gaseous detection systems, and using three neutron-converting reactions considered standard in different energy regions is reported. The results of the various measurements have been combined, yielding an evaluated neutron energy distribution in a wide energy range, from 2meV to 100MeV, with an accuracy ranging from 2%, at low energy, to 6% in the high-energy region. In addition, an absolute normalization of the n_TOF-EAR2 neutron flux has been obtained by means of an activation measurement performed with
197
Au foils in the beam.
A fast ionization chamber for fission cross-section measurements at n_TOF Calviani, M.; Cennini, P.; Karadimos, D. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2008, Letnik:
594, Številka:
2
Journal Article
Recenzirano
An ionization chamber with fast timing properties was built at CERN for measuring fission cross-sections of minor actinides at the n_TOF neutron beam. The design of this new chamber and of the ...front-end electronics was optimized to match the innovative features of the n_TOF facility, in particular the high instantaneous neutron flux and low background. For the most radioactive isotopes, a special version of the chamber, designed according to the ISO2919 standards, was built in order to comply with the radioprotection requirements at CERN. The detector and front-end electronics are here described, together with the simulated and measured response to fission fragments and α-particles. The performances of the chamber during the first measurement campaign at n_TOF are presented, focusing in particular on the fast time response, the good background rejection capability, low-background and high detection efficiency.
The article presents the results of corrosion processes, kinetics and changes in the oxide layer modeling using MASKA-LM software complex. The complex is intended for a numerical simulation of ...three-dimensional non-stationary processes of mass transfer and interaction of impurity components in a heavy liquid metal coolant (HLMC: lead, lead-bismuth). The software complex is based on the numerical solution of coupled three-dimensional equations of hydrodynamics, heat transfer, formation and convective-diffusive transport of chemically interacting components of impurities.
Examples of calculations of mass transfer processes and interaction of impurity components in HLMC, formation of protective oxide films on the surfaces of steels are given to justify the coolant technology.
The neutron capture cross sections of several unstable nuclides acting as branching points in the s process are crucial for stellar nucleosynthesis studies. The unstable Tm171 (t1/2=1.92 yr) is part ...of the branching around mass A∼170 but its neutron capture cross section as a function of the neutron energy is not known to date. In this work, following the production for the first time of more than 5 mg of Tm171 at the high-flux reactor Institut Laue-Langevin in France, a sample was produced at the Paul Scherrer Institute in Switzerland. Two complementary experiments were carried out at the neutron time-of-flight facility (n_TOF) at CERN in Switzerland and at the SARAF liquid lithium target facility at Soreq Nuclear Research Center in Israel by time of flight and activation, respectively. The result of the time-of-flight experiment consists of the first ever set of resonance parameters and the corresponding average resonance parameters, allowing us to make an estimation of the Maxwellian-averaged cross sections (MACS) by extrapolation. The activation measurement provides a direct and more precise measurement of the MACS at 30 keV: 384(40) mb, with which the estimation from the n_TOF data agree at the limit of 1 standard deviation. This value is 2.6 times lower than the JEFF-3.3 and ENDF/B-VIII evaluations, 25% lower than that of the Bao et al. compilation, and 1.6 times larger than the value recommended in the KADoNiS (v1) database, based on the only previous experiment. Our result affects the nucleosynthesis at the A∼170 branching, namely, the Yb171 abundance increases in the material lost by asymptotic giant branch stars, providing a better match to the available pre-solar SiC grain measurements compared to the calculations based on the current JEFF-3.3 model-based evaluation.
We have measured the neutron capture cross sections of the stable magnesium isotopes 24,25,26Mg in the
energy range of interest to the s process using the neutron time-of-flight facility n_TOF at ...CERN. Capture
events from a natural metal sample and from samples enriched in 25Mg and 26Mg were recorded using the
total energy method based on C6
2H6 detectors. Neutron resonance parameters were extracted by a simultaneous
resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample.
Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of
100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross
section for 24Mg, 25Mg, and 26Mg are 3.8±0.2 mb, 4.1±0.6 mb, and 0.14±0.01 mb, respectively.
73Ge(n,γ) cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results ...indicate that the stellar cross section at kT=30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of 73Ge produced in stars, which would explain the low isotopic abundance of 73Ge in the solar system.
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