Diffusion Compton

Résumé

En physique, la diffusion Compton (aussi appelée effet Compton) est une diffusion élastique (reposant sur la conservation de l'énergie cinétique globale du système étudié) lorsqu'on considère un électron libre, mais inélastique pour un électron lié. Ce phénomène s'observe lorsqu'un photon incident entre en collision avec un électron libre (ou plus précisément avec un électron faiblement lié) d'un atome. Au cours de ce processus, l'électron est éjecté de l'atome, qui est donc ionisé, tandis qu'un photon est diffusé. Arthur Compton a, en 1923, observé l'allongement de la longueur d'onde du photon dans cette diffusion, effet auquel on a attribué son nom. L'expérience de Compton devint l'ultime observation qui convainquit la plupart des physiciens que la lumière peut se comporter comme un faisceau de particules dont l'énergie est proportionnelle à la fréquence (ou inversement à la longueur d'onde). Cet effet est important en physique car il montre que la lumière ne peut pas être unique

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https://fr.wikipedia.org/wiki/Diffusion_Compton

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Cours associés (75)

Presentation of particle properties, their symmetries and interactions. Introduction to quantum electrodynamics and to the Feynman rules.

The goal of the course is to introduce relativistic quantum field theory as the conceptual and mathematical framework describing fundamental interactions.

The course relates on the use of electromagnetic (X-Ray) and corpuscular (electrons) radiations for physical and chemical analysis of solid materials.

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Séances de cours associées (221)

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Survival of rotational alignment in H-2 scattering from Si(100)

Christopher Scott Reilly

We report a state-prepared, state-resolved study of rotational scattering of a diatomic molecule from a solid surface. Specifically, H-2 molecules with 80 meV kinetic energy are rotationally aligned in the j = 3 rotational state via stimulated Raman pumping and then scattered from a Si(100) surface at normal incidence. The rotational alignment of the scattered molecules is determined by measuring, for both the incident and scattered molecules, the ionization yield of a probe laser, tuned to selectively ionize molecules in the j = 3 rotation level, as the probe laser polarization is rotated. The measurement is performed for two initial rotational alignments: a "helicoptering " alignment with the bonds constrained to lie primarily parallel to the surface and a "cartwheeling " alignment with the bonds lying primarily normal to the surface. For both initial alignments, the modulation of the probe ionization yield with laser polarization for the scattered molecules is pronounced, although significantly weaker than the modulation measured for the incident molecules. This indicates a significant modification but not a complete elimination of the initial alignment. The modulation is found to be stronger for the scattered molecules originating in the cartwheeling alignment than for the helicoptering alignment. These results contribute toward an improved understanding of the role of rotational motion in molecule-surface dynamics.

AIP Publishing2021

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Diffusion de neutrons de 14 MeV par le carbone 12

Claude Joseph

The angular distributions of the differential cross-sections for scattering of 14,1 MeV neutrons from 12C, Q = 0(0+); – 4,43(2+); – 7,65(0+) and – 9,63(8–) MeV, have been measured using a time-of-flight spectrometer. An indication can be found of the excitation of a wide level at about 10 MeV. A Monte-Carlo programme has been worked up and used to correct the results for multiple scattering; it calculates time-of-flight spectra which can be compared with the measured ones in order to deduce the best values of the cross-sections. The results are finally confronted with other experimental determinations and existing theoretical predictions.

s.n.1967

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The Neutron Scattering Structure Factor

Jérôme Egger

In the experience of neutron scattering, the structure factor is a value that can be almost directly measured (through the differential inelastic neutron scattering cross section). Thus it can be interesting to have a calculation which could give a theoretical point of view, even if the system used in the calculation cannot be as complex as in the real case. Although this calculation (of a simplified system) could be a bad representation of the real system, it is already a point of comparison which yields finally to a better understanding. The present work has the aim to provide a useful matlab code for the computation of the structure factor of small magnetic cluster in “spin-only” scattering. A concrete exemple and the result for a special configuration will be also given.

2010

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