Superheated drop detectors can be used for in-phantom dosimetry in a therapeutic neutron radiation field

Thèse de doctorat annexe - UCL, 199

Mesures de sections efficaces doublement différentielles de particules chargées légères induites par neutrons rapides sur 16 O et 27 Al (En=25-65 MeV).

La dissertations présente les mesures expérimentales de sections efficaces doublement différentielles de production de particules légères (protons, deutons, tritons et alphas) induites par des neutrons rapides sur l'oxygène et l'aluminium, à neuf énergies de neutrons incidents. Les distributions angulaires couvrent 15 angles allant de 20° à 160° par pas de 10°. Pour les protons et deutons, les distributions angulaires sont complètes à toutes les énergies de neutrons. Dans le cas des tritons et alphas, du à une pauvre statistique, suels des spectres en énergie aux angles de l'hémisphère avant (entre 20° et 80°) ont pu être extraits, pour des énergies de neutrons à 62.7 MeV. Les mesures ont été prises au cyclotron de Louvain-la-Neuve (CYCLONE) où les neutrons sont produits en envoyant un faisceau de protons de 65 MeV sur une cible de lithium naturel. Le spectre de neutrons est composé d'un pic monocinétique à haute énergie (62.7 MeV) suivi d'une longue queue de neutrons d'énergie plus basse. Les données sur l'oxygène et l'aluminium ont été obtenues en plaçant successibement des cibles de Al2O3 et de Al dans la chambre à réaction. Les données sur oxygène sont obtenues par soustraction des spectres mesurés avec les deux cibles. Les distributions angulaires des spectres d'émission sont extrapolées vers les angles extrêmes (2.5°, 10°, 170° et 177.5°) à l'aide d'une formule simple. Celle-ci est également utilisées pour interpoler les données dans le cas où il y a des angles manquants et pour exptrapoler les distributions angulaires limitées à l'hémisphères avant. Obtenant ainsi un bon recouvrement angulaire, des sections efficaces différentielles en énergie do/dE pour les quatres types de particules sont déduites. De plus, après extrapolation en dessous des seuils de détections, des sections efficaces totales de production sont déterminées. A partir des sections efficaces microscopiques, les facteurs kerma partiels (protons, deutons, tritons et alphas) pour l'oxygène et l'aluminium, sont déduits aux neufs énergies de neutrons incidents. Une simple procédure basée sur la cinématique de réaction et une paramétrisation de la section efficace totale de production de chaque particule est développée pour extrapoler les facteurs kerma partiels jusqu'aux seuils en énergie des différentes réactions. En se basant sur des distributions angulaires de sections efficaces de diffusion élastique existantes, des facteurs kerma pour le recul élastique sont calculés et rapportés pour des énergies de neutrons incidents entre 3.5 et 26 MeV. De cette manière, on étend les facteurs kerma élastiques de la littérature, à des énergies inférieures à 20 MeV. Des facteurs kerma totaux pour oxygène et aluminium sont également présentés.(PHYS 3)--UCL, 199

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”

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

Secondary light charged particle emission from the interaction of 25- to 65-MeV neutrons on silicon

Double-differential cross sections for the production of protons, deuterons, tritons, and alpha particles from a silicon target were determined using fast incident neutrons. The inclusive charged particle emission spectra were measured at six laboratory angles, 20, 40, 60, 70, 110, and 140 deg, over the neutron energy range of 25 to 65 MeV. Representative results are shown for the cross-section differentials in energy and angle as well as for angle-integrated cross sections. The spectra are compared to existing data and with predictions from nuclear model calculations. Since the data for 62.7-MeV incident neutrons are the most complete, we emphasized these results; from the experimental energy-differential cross sections, the total charged particle production cross sections are determined as well as the partial and total kerma coefficients for silicon. Moreover, a comparison is done with our data on aluminum, for which exists a consistent set of measured cross sections in the same neutron energy region.Anglai

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

Experimental double-differential cross sections and derived kerma factors for oxygen at incident neutron energies from reaction thresholds to 65 MeV.

The double-differential cross sections (energy spectra) for the (n, px), (n, dx), (n, tx) and (n, rx) reactions on oxygen have been measured for nine incident neutron energies in the range 25 to 65 MeV at lab angles between 20 degrees and 160 degrees in steps of 10 degrees. From these measurements, the energy differential cross sections have been determined and consequently the partial and total kerma factors. Based on the obtained experimental partial kerma factors in the incident neutron energy range 25-65 MeV, a procedure is proposed for the extrapolation of these values to the reaction threshold energy of each measured reaction channel. Results of the experimental double-differential, energy differential and total cross sections are presented. The deduced partial and total kerma factors of the present work are compared with results of previous measurements and theoretical predictions

Neutron-proton differential cross section measurements for E(n) from 28 to 75 MeV

Experimental measurements of differential cross-sections for neutron-proton scattering are reported for 12 incident neutron energies between 28 and 75 MeV. Data are compared with predictions of different theoretical models and with other experimental results. (C) 1997 Elsevier Science B.V

Neutron-proton differential cross section measurements for E/sub n / from 28 to 75 MeV

Experimental measurements of differential cross-sections for neutron-proton scattering are reported for 12 incident neutron energies between 28 and 75 MeV. Data are compared with predictions of different theoretical models and with other experimental results.Anglai

Light charged particle production in fast neutron-induced reactions on carbon (E-n=20 to 75 MeV) (I). Protons and deuterons

Double-differential cross sections for proton and deuteron emission in fast neutron-induced reactions on carbon are reported at several incident neutron energies between 20 and 75 MeV. Angular distributions were measured at 15 laboratory angles between 20 degrees and 160 degrees. Procedures for data taking and data reduction are shortly presented. Deduced energy-differential, angle-differential and total cross sections are also reported. Experimental cross sections are compared with existing experimental data and with theoretical model calculations. (C) 2000 Elsevier Science B.V. All rights reserved