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Theoretical study of the paramagnetic scattering of neutrons; Etude theorique de la diffusion paramagnetique des neutrons

Abstract

General paramagnetic scattering of neutrons is investigated in the situation where the orbital moment of the magnetic scattering ions is not quenched. The general relevant expression of the cross-section is given. The proceeding results are applied to rare earths and iron group ions. It is shown that if crystalline actions lift the free ion ground state degeneracy the neutron may induce transitions between the various levels, the distances of which are typically of the order of several hundred cm{sup -1}. The various scattering cross-sections (elastic and inelastic) are calculated for the rare earths in a cubic crystal field, for the holmium and erbium sesquioxide and for the anhydrous iron chloride (Cl{sub 2}Fe). These cross-sections are high enough to allow for an experimental detection, thus providing a direct determination of the levels distances through the measurement of the neutron wave-length shift. Moreover it is shown that, for neodymium, holmium, erbium, the total cross-section for neutrons of one angstrom wave length is rather insensitive to the crystal field effects. The results are then compared with the available experimental studies. The influence of the orbital moment on the angular dependence of the scattering for polarised ions is then investigated. The well-known formula: I  More>>
Authors:
Saint-James, D [1] 
  1. Commissariat a l'Energie Atomique, Saclay (France). Centre d'Etudes Nucleaires
Publication Date:
Feb 15, 1962
Product Type:
Thesis/Dissertation
Report Number:
CEA-R-1996
Resource Relation:
Other Information: TH: These ES sciences physiques; 26 refs
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; ANGULAR MOMENTUM OPERATORS; CLEBSCH-GORDAN COEFFICIENTS; CROSS SECTIONS; CRYSTAL FIELD; ELASTIC SCATTERING; ELECTRON-NEUTRON INTERACTIONS; ENERGY-LEVEL TRANSITIONS; ERBIUM IONS; FORM FACTORS; HOLMIUM IONS; INELASTIC SCATTERING; IRON CHLORIDES; L-S COUPLING; LINE WIDTHS; MATRIX ELEMENTS; NEODYMIUM IONS; NEUTRON DIFFRACTION; NEUTRON SPECTRA; ORBITAL ANGULAR MOMENTUM; PARAMAGNETISM; RARE EARTHS; SPHERICAL HARMONICS METHOD; TEMPERATURE DEPENDENCE; WAVE FUNCTIONS
OSTI ID:
20972244
Research Organizations:
CEA Saclay, 91 - Gif-sur-Yvette (France); Faculte des Sciences de l'Universite de Paris, 75 (France)
Country of Origin:
France
Language:
French
Other Identifying Numbers:
TRN: FR07R1996001564
Availability:
Available from INIS in electronic form
Submitting Site:
FRN
Size:
152 pages
Announcement Date:
Jan 17, 2008

Citation Formats

Saint-James, D. Theoretical study of the paramagnetic scattering of neutrons; Etude theorique de la diffusion paramagnetique des neutrons. France: N. p., 1962. Web.
Saint-James, D. Theoretical study of the paramagnetic scattering of neutrons; Etude theorique de la diffusion paramagnetique des neutrons. France.
Saint-James, D. 1962. "Theoretical study of the paramagnetic scattering of neutrons; Etude theorique de la diffusion paramagnetique des neutrons." France.
@misc{etde_20972244,
title = {Theoretical study of the paramagnetic scattering of neutrons; Etude theorique de la diffusion paramagnetique des neutrons}
author = {Saint-James, D}
abstractNote = {General paramagnetic scattering of neutrons is investigated in the situation where the orbital moment of the magnetic scattering ions is not quenched. The general relevant expression of the cross-section is given. The proceeding results are applied to rare earths and iron group ions. It is shown that if crystalline actions lift the free ion ground state degeneracy the neutron may induce transitions between the various levels, the distances of which are typically of the order of several hundred cm{sup -1}. The various scattering cross-sections (elastic and inelastic) are calculated for the rare earths in a cubic crystal field, for the holmium and erbium sesquioxide and for the anhydrous iron chloride (Cl{sub 2}Fe). These cross-sections are high enough to allow for an experimental detection, thus providing a direct determination of the levels distances through the measurement of the neutron wave-length shift. Moreover it is shown that, for neodymium, holmium, erbium, the total cross-section for neutrons of one angstrom wave length is rather insensitive to the crystal field effects. The results are then compared with the available experimental studies. The influence of the orbital moment on the angular dependence of the scattering for polarised ions is then investigated. The well-known formula: I = I{sub 0}sin{sup 2}{beta} is only an approximation, the validity of which is discussed. (author) [French] On envisage le cas general de la diffusion paramagnetique de neutrons. Le moment orbital des ions magnetiques ne peut etre considere comme bloque. On donne l'expression generale de la section efficace. Les resultats obtenus sont appliques au cas des terres rares et des ions du groupe du fer. On montre que, si les actions cristallines levent la degenerescence du niveau fondamental de l'ion libre, le neutron peut induire des transitions entre les divers sous-niveaux, dont la distance est ordinairement de l'ordre de quelques centaines de cm{sup -1}. La section efficace des diverses diffusions (elastique et inelastiques) est calculee pour les terres rares soumises a l'action d'un champ cristallin de symetrie cubique, pour les sesquioxydes d'holmium et d'erbium et pour le chlorure ferreux anhydre (Cl{sub 2}Fe). Elle est suffisamment forte pour permettre une detection experimentale, fournissant ainsi une determination directe de la distance des niveaux par mesure de la variation de longueur d'onde du neutron. Il est, de plus, remarquable que, dans le cas du neodyme, de l'holium et de l'erbium, la section efficace totale calculee pour des neutrons de longueur d'onde aux alentours de l'angstrom soit peu sensible aux effets du champ cristallin. On compare les resultats des calculs ci-dessus aux etudes experimentales existantes. On examine egalement l'influence du moment orbital sur la dependance angulaire de la diffusion pour des ions polarises. La loi I = I{sub 0}sin{sup 2}{beta} n'est qu'approchee; on en donne les limites de validite. On envisage enfin l'influence des interactions d'echange entre les ions magnetiques. Les raies de diffusion elastiques et inelastiques sont elargies. Le comportement de la largeur de raie, avec la longueur du vecteur de diffusion k, est different de celui obtenu dans le cas ou le niveau fondamental de l'ion magnetique est defini par un moment cinetique J . La largeur de raie ne tend pas vers zero avec K. (auteur)}
place = {France}
year = {1962}
month = {Feb}
}