Publication: Determinación de plutonio y americio mediante centelleo líquido bifásico
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2017-05-12
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Universidad Complutense de Madrid
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Abstract
La humanidad ha estado siempre expuesta a fuentes de ionización naturales: rayos cósmicos, sustancias radiactivas que forman parte de nuestro cuerpo, como 40K, 14C, etc y materiales radiactivos procedentes de la corteza terrestre, muchos de los cuales se han incorporado a los materiales de construcción, al aire y a la comida. Tres cuartas partes de la radiactividad que hay en el medio ambiente proceden de los elementos naturales. Estas fuentes de radiación se llaman radiación de fondo o radiación natural. Además de la radiación de fondo, el hombre está expuesto a fuentes de radiación que él mismo ha creado. Estas fuentes de radiación incluyen aplicaciones de radioisótopos en medicina, la industria y la investigación, la producción de energía, las pruebas nucleares en la atmósfera y todos los materiales de desecho que estas actividades implican. La determinación precisa de la actividad de radionucleidos de radiación alfa en residuos que contienen mezclas de emisores alfa y beta-gamma es muy importante, desde el punto de vista de seguridad a largo plazo en el almacenamiento de residuos de media y baja actividad, puesto que la actividad permitida en dicho emplazamiento está muy limitada. En la serie de actínidos, los elementos de mayor interés como contaminantes ambientales son el neptunio, americio, curio y plutonio, siendo este último el que se produce en mayor cantidad que cualquier otro. La presente Tesis Doctoral se centra en la determinación de Pu y Am mediante una técnica novedosa y rápida. Estos elementos se analizan habitualmente una vez realizadas varias etapas previas de separación (resinas de intercambio iónico, extracción líquido-líquido o precipitación) mediante espectrometría alfa, técnica que permite calcular la actividad de cada isótopo (238Pu, 239/240Pu, 241Am, …), como por centelleo líquido convencional, determinándose la actividad total de cada elemento (Pu, Am,…). Sin embargo, es posible calcular la actividad de Pu alfa total y de Am, haciendo una única separación radioquímica en el vial, utilizando para ello una mezcla de disoluciones de centelleo que son inmiscibles y específicas para cada radionucleido. Esta técnica se conoce como centelleo líquido bifásico...
Humankind has always been exposed to natural sources of ionizing radiation: cosmic rays, radioactive materials found in the earth's crust, many of which are incorporated into building materials, air and food, and even radioactive substances found within the human body (40K, 14C, etc). These sources of radiation are called background radiation or natural radiation and are part of the environment. In addition to background radiation, man is exposed to radiation sources that he has created. They include applications of radioisotopes in medicine, industry and research, power production, nuclear tests in the atmosphere and all the waste materials that these activities involve. Hence, the radioactive waste produced must be characterized and managed properly. In particular, the radiological characterization of waste streams and environmental samples containing pure beta emitters or actinides radionuclides poses special problems in radiological characterization and monitoring. These difficulties increase when the number of radionuclides in the sample increases. Due to the high radiotoxicity and long half-lives radioactive, the content of alpha emitters in the storage of low and intermediate activity waste is very limited. In the actinides series, the greatest interests as environmental contaminants are neptunium, plutonium, americium and curium. However, plutonium has been produced in greater quantity than any other transuranic elements. The present Doctoral Thesis is focused on Pu and Am determination. To determine them in samples in which these radionuclides are present, require a complex physical separation, either measured by the usual technique of alpha spectrometry or measured by liquid scintillation, because the difference of emission energy of these radionuclides is so small that it is impossible to determine them together. However, it is possible to determine gross Pu activity and gross Am activity, doing an easy radiochemical separation within the vial using a mixture of immiscible scintillator solutions and specific for each radionuclide. This technique is known as biphasic liquid scintillation counting...
Humankind has always been exposed to natural sources of ionizing radiation: cosmic rays, radioactive materials found in the earth's crust, many of which are incorporated into building materials, air and food, and even radioactive substances found within the human body (40K, 14C, etc). These sources of radiation are called background radiation or natural radiation and are part of the environment. In addition to background radiation, man is exposed to radiation sources that he has created. They include applications of radioisotopes in medicine, industry and research, power production, nuclear tests in the atmosphere and all the waste materials that these activities involve. Hence, the radioactive waste produced must be characterized and managed properly. In particular, the radiological characterization of waste streams and environmental samples containing pure beta emitters or actinides radionuclides poses special problems in radiological characterization and monitoring. These difficulties increase when the number of radionuclides in the sample increases. Due to the high radiotoxicity and long half-lives radioactive, the content of alpha emitters in the storage of low and intermediate activity waste is very limited. In the actinides series, the greatest interests as environmental contaminants are neptunium, plutonium, americium and curium. However, plutonium has been produced in greater quantity than any other transuranic elements. The present Doctoral Thesis is focused on Pu and Am determination. To determine them in samples in which these radionuclides are present, require a complex physical separation, either measured by the usual technique of alpha spectrometry or measured by liquid scintillation, because the difference of emission energy of these radionuclides is so small that it is impossible to determine them together. However, it is possible to determine gross Pu activity and gross Am activity, doing an easy radiochemical separation within the vial using a mixture of immiscible scintillator solutions and specific for each radionuclide. This technique is known as biphasic liquid scintillation counting...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Analítica, leída el 14/01/2016