Structure électronique locale des alliages fortement dilués BAl et BCu

Doctorat en sciences physiques -- UCL, 199

The energetic Particle Telescope (EPT) concept and performances

The forecast of energetic particle fluxes on time scales of hours to weeks, at a given position in space, can be achieved on the basis of experimentally determined particle lifetimes and real-time measurements of contamination-free spectra. Such elaborated measurements can be provided by the Energetic Particle Telescope (EPT) without any further post-processing. This instrument directly acquires energy spectra of electrons (0.2 – 10 MeV), protons (4 – 300 MeV), α-particles (16 – 1000 MeV) and heavier ions (up to 300 MeV/nucleon). The EPT was developed at the Center for Space Radiations – UCL-Belgium. This paper contains a brief description of the EPT concept and the definition of channels along with a more detailed presentation of the general performances based on the intrinsic detection efficiency functions and the validation test results from an Engineering Model. The EPT capabilities for space-weather related applications are highlighted by an example of electron flux forecast

Depth profile determination of extremely diluted polarized ions implanted in metals

A direct method for the determination of the depth profile of implanted polarized probes is described. It has been applied to measure the depth profile of B-12 nuclei implanted at an atomic concentration of 10(-16) in polycrystalline gold. The results prove the ability of this method to measure the depth distribution of implanted nuclei with an unknown energy distribution, which is typical for a polarized beam emerging from a succession of nuclear reactions or electromagnetic interactions

Characterization of Solar Energetic H and He Spectra Measured by the Energetic Particle Telescope (EPT) On-Board PROBA-V During the January 2014 SEP Event

On January 6, 2014 a Solar Energetic Particle (SEP) event started that led to a 1030 cm−2s−1sr−1 peak flux of E > 10 MeV protons on January 9, 2014 at geosynchronous orbit, an event exceeded only by about 15% of all SEP events. Such high flux events contribute the most to solar event-induced radiation effects in space equipment, while being easy to characterize based on data acquired by spectrometers, such as the EPT. The EPT instrument provides fluxes of electrons (0.5–20 MeV), H (9.5–300 MeV) and He (38–1200 MeV) ions. It presently flies on the PROBA-V satellite, launched into a Low Earth Orbit on May 7, 2013. As it has been reported that the He contribution to Total Non-Ionizing Dose (TNID) may be comparable to that of H in representative space environments, a data analysis to identify periods of high He flux as compared to H, and conditions under which both ions must be accounted for during radiation effect analyses, was performed. From the study of the positional variation of solar H and He fluxes, a formulation of the minimum L-value reached by these particles for a given rigidity is provided. The shape of solar H and He energy spectra as well as the H/He fluence ratio and pitch angle distributions are characterized. The contribution of He compared to H for Total Ionizing Dose (TID) and TNID effects is below 5% for devices shielded by >2mm Al

Angular Distribution of Protons Measured by the Energetic Particle Telescope on PROBA-V

Angular distribution and contamination of proton spectra measured at LEO are considered as possible sources of discrepancies between fluxes obtained by different instruments. In particular, not accounted for pitch angle distribution and East/West asymmetry of energetic proton fluxes have been suspected of leading to the reported underestimates of these fluxes by the NASA Model AP8. The Energetic Particle Telescope (EPT) was designed as a science-class instrument aimed at providing uncontaminated fluxes of electrons (0.5 – 20 MeV), protons (9.5 – 300 MeV) and α-particles (38 – 1200 MeV) getting into the instrument from within a well-defined Field Of View (FOV). The PROBA-V satellite with EPT was launched on May 7th, 2013 on a LEO, 820 km altitude, 98.7° inclination and a 10:30 – 11:30 Local Time at Descending Node. Based on the data acquired by the EPT on board PROBA-V, we account for flux angular distribution effects to provide a definitive reply to the basic question: “does AP8 underestimate E > 100 MeV proton fluxes around B/B0 = 1.1, L = 1.3”

Study of correlations between waves and particle fluxes measured on board the DEMETER satellite

The topic of relativistic electron dynamics in the outer radiation belt has received considerable attention for many years. Nevertheless, the problem of understanding the physical phenomenon involved is far from being resolved. In this paper, we use DEMETER observations to examine the variations of the energetic electron fluxes and ELF/VLF wave intensities in the inner magnetosphere during the intense 8 November 2004 magnetic storm. Electron flux spectra and associated wave intensity spectra are analysed throughout the magnetic storm and common characteristics or differences to other storm events are retained. The overall objective of this study is to identify and derive parameters that are relevant for particle flux modelling; the time constant characterizing the persistent decay after particle enhancement was found to be one of these important model parameters. The analysis of the 8 November 2004 event reveals that for L-shell parameter higher than similar to 4, all electron flux dropout is observed during the storm's main phase for electrons in the energy range 0.1-1 MeV, as has been reported from other measurements. Characteristic wave spectra accompanying this phase are analysed. They show a typical enhancement in the frequency range 0.3-10 kHz at onset for all L-shell values under consideration (2 < L < 5). During the first stage of the recovery phase, the electron fluxes are increased to a level higher than the pre-storm level, whereas the level of wave intensity in the frequency range observed below 300 Hz is at its highest. In the second stage, the particle flux decrease goes hand in hand with a global wave activity decline, the relaxation time of the latter being smaller than the former's one. In some other cases, long-lasting electron enhancement associated with constant wave activity has been observed during this latter stage. For the above mentioned storm, while at low L values the decay time constants are higher for low energy electrons than for high energy electrons, this order is reversed at high L values. At about L = 3.6 the time constant is independent of electron energy. (C) 2008 COSPAR. Published by Elsevier Ltd. All rights reserved

Etude de r sidus du noyau compos apr(s vaporation d'un nucl on

SIGLEBSE B224211V / UCL - Université Catholique de LouvainBEBelgiu

The Energetic Particle Telescope (EPT) on Board PROBA-V: Description of a New Science-Class Instrument for Particle Detection in Space

This paper provides a detailed description of the Energetic Particle Telescope (EPT) accommodated on board the PROBA-V satellite launched on May 7th, 2013 on a LEO, 820 km altitude, 98.7° inclination and a 10:30 – 11:30 Local Time at Descending Node. The EPT is an ionizing particle spectrometer that was designed based on a new concept and the most advanced signal processing technologies: it performs in-flight electron and ion discrimination and classifies each detected particle in its corresponding physical channels from which the incident spectrum can be readily reconstructed. The detector measures electron fluxes in the energy range 0.5 - 20 MeV, proton fluxes in the energy range 9.5 - 300 MeV and He-ion fluxes between 38 and 1200 MeV. The EPT is a modular configurable instrument with customizable maximum energy, field of view angle, geometrical factor and angular resolution. Therefore, the features of the currently flying instrument may slightly differ from those described in past or future configurations. After a description of the instrument along with the data acquisition and analysis procedures, the first particle fluxes measured by the EPT will be shown and discussed. The web-site located at http://web.csr.ucl.ac.be/csr_web/probav/ which daily displays measured fluxes and other related studies will also be briefly described

The transient observation-based particle (TOP) model and its potential application in radiation effects evaluation

The evaluation of the radiation hazards on components used in space environment is based on the knowledge of the radiation level encountered on orbit. The models that are widely used to assess the near-Earth environment for a given mission are empirical trapped radiation models derived from a compilation of spacecraft measurements. However, these models are static and hence are not suited for describing the short timescale variations of geomagnetic conditions. The transient observation-based particle (TOP)-model tends to break with this classical approach by introducing dynamic features based on the observation and characterization of transient particle flux events in addition to classical mapping of steady-state flux levels. In order to get a preliminary version of an operational model (actually only available for electrons at low Earth orbit, LEO), (i) the steady-state flux level, (ii) the flux enhancements probability distribution functions, and (iii) the flux decay-time constants (at given energy and positions in space) were determined, and an original dynamic model skeleton with these input parameters has been developed. The methodology is fully described and first flux predictions from the model are presented. In order to evaluate the net effects of radiation on a component, it is important to have an efficient tool that calculates the transfer of the outer radiation environment through the spacecraft material, toward the location of the component under investigation. Using the TOP-model space radiation fluxes and the transmitted radiation environment characteristics derived through GEANT4 calculations, a case study for electron flux/dose variations in a small silicon volume is performed. Potential cases are assessed where the dynamic of the spacecraft radiation environment may have an impact on the observed radiation effects