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Master's Dissertation
DOI
10.11606/D.43.1999.tde-16022011-194341
Document
Author
Full name
Marcus Kliewer
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1999
Supervisor
Committee
Lepine, Alinka (President)
Medina, Nilberto Heder
Saxena, Rajendra Narain
Title in Portuguese
Método de Espectroscopia de Mistura de Níveis para Medida de Momentos de Quadrupolo Nucleares
Keywords in Portuguese
Campos hiperfinos
Fisica Nuclear
Metodos experimentais
Momento Quadrupolo magnetico
Abstract in Portuguese
Momentos de quadrupólo elétricos de estados isoméricos nucleares com vidas médias entre 10 nanosegundos e 100 milisegundos podem ser medidos com o método Espectroscopia de Mistura de Níveis (Level Mixing Spectroscopy- LEMS), utilizando campos magnéticos variáveis aplicados em núcleos implantados em materiais hospedeiros que possuam gradientes de campo elétrico. O Campo magnético externo pode ser substituido pelo campo hiperfino de materiais ferromagnéticos e sua variação poderia ser controlada variando a temperatura. O objetivo deste trabalho é verificar a viabilidade desta substituição. Implementamos o método LEMS no Laboratório Pelletron usando como caso teste o estado isomérico de 398 KeV do 69Ge que possui todas as suas propriedades nucleares conhecidas (meia vida, spin, momento magnético, momento de quadrupolo elétrico). Ele foi produzido pela reação 56Fe(16O, 2pn)69Ge com o feixe de 16O à 53 MeV (LAB) de energia, e depois implantado em Gadolínio que é ferromagnético abaixo de Tc = 289K. Medimos a anisotropia da radiação gama emitida por esse núcleo em função da temperatura. A comparação entre as medidas da anisotropia em função da temperatura, com medidas da anisotropia em função do campo magnético externo, feita pelo grupo de Leuven/Bélgica, nos levou a duas interpretações possíveis. Na primeira, supondo a interação elétrica constante e independente da temperatura, obtemos um campo magnético hiperfino anômalo para o Gd. Na segunda análise, obtivemos o campo hiperfino variando linearmente com a magnetização, admitindo gradientes de campo elétrico dependentes da temperatura. Medidas futuras usando monocristal de Gd poderão resolver esta ambiguidade, bem como medidas TDPAD (Time Diferencial Perturbed Angular Distribuition) em função da temperatura, na qual se mede diretamente o campo hiperfino.
Title in English
Level Mixing Spectroscopy method to measure the Nuclear Quadrupole Momentum
Keywords in English
Experimental method
Nuclear Physics
Quadrupole Nuclear Momentum
Abstract in English
The Level Mixing Spectroscopy method allows to measure the eletric quadrupole moments of high spin isomeric nuclear states (10ns < t < 100ms) produced in nuclear reactions. The magnetic interaction is usualy created by an intense external magnetic field. The eletric quadrupole interaction can be created by recoi-implantation of the nuclei in non-cub crystals, used as hosts. The external magnetic field can then be replaced by the hiperfine fields of ferromagnetic materials, controling its intensity by temperature variation. The purpose of the research performed for this work is to verify the viability of this replacement. We adapt the LEMS method to be used in the Pelletron Laboratory. We choose the isomeric state at 398 KeV exitation energy in the 69Ge nucleus as a test case, because it has all nuclear properties well known (half-life, spin, magnetic moment, eletric quadrupole moment). It was produced by the 56Fe(16O, 2pn)69Ge reaction, with a 16O beam at 53 MeV, and implanted and stopped in a Gadolinium host, which is a ferromagnet from low temperatures up to Tc=289 K. We measure the anisotropy of the emitted gama ray as a function of the temperature of the host. The comparison of this measurement with another of the anisotropy as a function of an external magnetic field strength, done by the Leuven/Belgium group, show us two possibilities. In the first, we suppose that the eletric interaction is cosntant and independent of temprature and we obtain an anomalous magnetic hyperfine field for Gd. In the second one, we obtain a hyperfine field that follows the magnetization if we assume eletric field gradientes that are temperature dependent. New measurements by using Gd monocrystal and the TDPAD (Time Diferencial Perturbed Angular Distribution) method may solve this ambiguity.
 
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Publishing Date
2011-03-28
 
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