In the present work, the measurement of the
237
Np(n,f) cross section with reference to the standard
238
U(n,f) reaction was performed for the first time with a MicroMegas detector, especially ...developed at CERN, for these measurements, within the framework of the n_TOF Collaboration. The incident monoenergetic neutron beam with energies in the range 4.5-5.3MeV was produced via the
2
H(d,n) reaction at the neutron facility of the 5.5MV Tandem accelerator laboratory at NCSR “Demokritos”. The mass of the actinide content of the targets used and of their impurities was quantitatively determined via alpha spectroscopy. Furthermore, their thickness and homogeneity have been examined via the RBS (Rutherford Backscattering Spectrometry) technique. Monte Carlo simulations were carried out using the code MCNP5 implementing the neutron beam setup and the MicroMegas assembly in order to determine the neutron flux for each target, as well as the existence of possible low-energy neutrons due to scattering. Additional simulations with FLUKA were performed, studying the energy deposition of the fission fragments in the active area of the detector, in order to accurately estimate the detection efficiency. Fair discrimination of the heavy and light mass peaks of the fission fragments at the energy spectra was achieved. The present work is compared to existing evaluations and previous data which present discrepancies of up to 8% within the same energy range.
The measurement of the 237Np(n,f) cross section with reference to the standard 238U(n,f) reaction was performed with a MicroMegas detector at the neutron facility of the 5.5 MV Tandem accelerator ...laboratory at NCSR “Demokritos”. The performance of the detector as far as the gain and resolution function are concerned will be presented.
Piccolo Micromegas: First in-core measurements in a nuclear reactor Pancin, J.; Andriamonje, S.; Aune, S. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2008, Letnik:
592, Številka:
1
Journal Article
Recenzirano
Odprti dostop
An Accelerator Driven System (ADS) consists in the coupling of an accelerator with a nuclear reactor. Such systems will need neutron detectors working in a wide energy range and insensitive to X- and
...γ
-rays. Micromegas technology has been proposed to achieve this goal. The ability of Micromegas to detect neutrons over a wide energy range has already been demonstrated and this detector is, under certain conditions, insensitive to
γ
-rays. A new Micromegas neutron detector called Piccolo Micromegas has been designed to get integrated neutron fluxes on different energy domains. For the first time, Piccolo Micromegas has been placed in the core of a nuclear reactor at Casaccia in Italy. The configuration of the detector will be presented as well as its functioning and the reasons of its insensitivity to
γ
-rays. The results of the operation of the detector will also be shown for low reactor power to high reactor power and some improvements will be suggested.
The design of Micromegas is offering, for several applications, substantial advantage in energy, spatial and time resolution, granularity on large surface and simplicity of construction. However the ...maximum achievable gain is limited, at high hadron rates, because of sparks induced by heavy ionizing particles produced by nuclear interactions. An issue to decrease drastically the sparking rate is to use the conversion space of the detector as a preamplification stage. In this paper, we will describe the design and laboratory results of new amplifying structures, based on the Micromegas concept that can be either used as a preamplification element or stand-alone detector for some specific applications.
Knowledge of neutron cross sections of various plutonium isotopes and other minor actinides is crucial for the design of advanced nuclear systems. The super(242)Pu(n,f) cross sections were measured ...at the CERN n_TOF facility, taking advantage of the wide energy range (from thermal to GeV) and the high instantaneous flux of the neutron beam. In this work, preliminary results are presented along with a theoretical cross section calculation performed with the EMPIRE code.
The neutron capture cross section of
232
Th has been measured relative to σ(n, γ) for
197
Au and σ(n,f) for
235
U in the energy range from 60 keV to 2 MeV. Neutrons were produced by the
7
Li(p,n) and ...T(p,n) reactions at the 4-MV Van de Graaff Accelerator of CEN Bordeaux-Gradignan. The activation technique was used, and the cross section was measured relative to the
197
Au(n,γ) standard cross section up to 1 MeV. The characteristic gamma lines of the product nuclei
233
Pa and
198
Au were measured with a 40% high-purity germanium detector. Above this energy, the reaction
235
U(n,f) was also used as a second standard, and the fission fragments were detected with a photovoltaic cell. The results, after applying the appropriate corrections, indicate that the cross sections are close to the JENDL-3 database values up to 800 keV and over 1.4 MeV. For energies in the intermediate range, our values are slightly lower than those from all the libraries.
Knowledge of neutron cross sections of various plutonium isotopes and other minor actinides is crucial for the design of advanced nuclear systems. The 242Pu(n,f) cross sections were measured at the ...CERN n_TOF facility, taking advantage of the wide energy range (from thermal to GeV) and the high instantaneous flux of the neutron beam. In this work, preliminary results are presented along with a theoretical cross section calculation performed with the EMPIRE code.
Neutron imaging with a Micromegas detector Andriamonje, S.; Dangendorf, V.; Espagnon, I. ...
IEEE Symposium Conference Record Nuclear Science 2004,
2004, Letnik:
3
Conference Proceeding
Odprti dostop
Due to its performances for neutron detection, the micropattern gaseous detector Micromegas is designed for neutron imaging. In this paper will be presented new results obtained with thermal neutrons ...near Orphee reactor at CEA Saclay. The goal of studies with a bi-dimensional detector was to tune different parameters in order to achieve the best spatial resolution which is around 160 mum (defined as the standard deviation) in double amplification mode and 180 mum in classical mode. Several 2D imaging tests have been carried out and an example, which shows different problems inherent in the substrate manufacturing, will be presented. Then, a tomographic section of a multi-wires cable, achieved with a one-dimensional Micromegas, will be presented. The high number of pillars sustaining the micromesh has lead to local inefficiencies, disturbing the tomographic reconstruction, but this result, the first tomography carried out with this kind of detector, is very encouraging.
We have observed delayed Kα photons emitted by 60 A MeV H-like and He-like krypton ions leaving a 37 μm silicon crystal, both for random and 〈110〉 axial alignment of the target. We could extract ...intrashell (2s→ 2p) excitation probabilities, which are compared with values deduced from PWBA calculations.
We summarize here the results of the TARC experiment whose main purpose is to demonstrate the possibility of using Adiabatic Resonance Crossing (ARC) to destroy efficiently Long-Lived Fission ...Fragments (LLFFs) in accelerator-driven systems and to validate a new simulation developed in the framework of the Energy Amplifier programme. An experimental set-up was installed in a CERN PS proton beam line to study how neutrons produced by spallation at relatively high energy ( E n ⩾1 MeV ) slow down quasi-adiabatically with almost flat isolethargic energy distribution and reach the capture resonance energy of an element to be transmuted where they will have a high probability of being captured. Precision measurements of energy and space distributions of spallation neutrons (using 2.5 and 3.5 GeV/ c protons) slowing down in a 3.3 m×3.3 m×3 m lead volume and of neutron capture rates on LLFFs 99 Tc, 129 I, and several other elements were performed. An appropriate formalism and appropriate computational tools necessary for the analysis and understanding of the data were developed and validated in detail. Our direct experimental observation of ARC demonstrates the possibility to destroy, in a parasitic mode, outside the Energy Amplifier core, large amounts of 99 Tc or 129 I at a rate exceeding the production rate, thereby making it practical to reduce correspondingly the existing stockpile of LLFFs. In addition, TARC opens up new possibilities for radioactive isotope production as an alternative to nuclear reactors, in particular for medical applications, as well as new possibilities for neutron research and industrial applications. (Elsevier)
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