Estudio de coincidencias ultra-rápidas de isótopos exóticos de Fe ricos en neutrones

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Atómica, Molecular y Nuclear, leída el 20-09-2013Uno de los pilares fundamentales de la estructura nuclear, tal y como la conocemos de los nucleos estables, es la existencia de numeros magicos. Los nucleos mas estables surgen de orbitales completamente llenos, orbitales cerrados, y dan lugar a los nagicos. En el valle de estabilidad dichos numeros son 8, 20, 28, 50, 82 y 126. La constante evolucion en la produccion, separacion e identicacion de nucleos exoticos, junto a una mejora en las tecnicas de deteccion, hace posible el estudio experimental de nucleos lejos del valle de estabilidad. Estos nucleos exoticos con numero supuestamente magicos no siempre tiene las propiedades que uno esperara. Al ir añadiendo o sustrayendo nucleones de un nucleo estable, la energía de partícula independiente se modifican y fuertes correlaciones octupolares aparecen, las cuales pueden neutralizar los saltos de capa del campo medio esferico. La investigacion de la evolucion de la estructura de capas lejos de la estabilidad se ha convertido en uno de los temas mas importantes en Física Nuclear. Investigaciones en este area tienen grandes implicaciones en astrofísica nuclear, ya que los nucleos exoticos juegan un papel crucial en los procesos de nucleosíntesis estelar que dan lugar a la formacion de los nucleos presentes en el Universo. El experimento IS474 se realizo en las instalaciones ISOLDE, CERN, donde se crearon isotopos de 59-66 Mn y su desintegracion estudiada. Esta tesis doctoral se centra en el estudio de isotopos ricos en neutrones (los impares 63;65Fe y el par 66Fe) empleando espectroscopía gamma y estudios de coincidencias retardadas avanzadas...Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Fast-timing study of Ga-81 from the beta decay of Zn-81

The beta-decay of Zn-81 to the neutron magic N = 50 nucleus Ga-81, with only three valence protons with respect to Ni-78, was investigated. The study was performed at the ISOLDE facility at CERN by means of gamma spectroscopy. The 81Zn half-life was determined to be T-1/2 = 290(4) ms while the beta-delayed neutron emission probability was measured as P-n = 23(4)%. The analysis of the beta-gated gamma-ray singles and gamma-gamma coincidences from the decay of Zn-81 provides 47 new levels and 70 new transitions in Ga-81. The beta(-)n decay of Zn-81 was observed and a new decay scheme into the odd-odd Ga-80 nucleus was established. The half-lives of the first and second excited states of Ga-81 were measured via the fast-timing method using LaBr3(Ce) detectors. The level scheme and transition rates are compared to large-scale shell-model calculations. The low-lying structure of (81)Gais interpreted in terms of the coupling of the three valence protons outside the doubly magic Ni-78 core

Continuous cultivation of photosynthetic microorganisms: approaches, applications and future trends

The possibility of using photosynthetic microorganisms, such as cyanobacteria and microalgae, for converting light and carbon dioxide into valuable biochemical products has raised the need for new cost-efficient processes ensuring a constant product quality. Food, feed, biofuels, cosmetics and pharmaceutics are among the sectors that can profit from the application of photosynthetic microorganisms. Biomass growth in a photobioreactor is a complex process influenced by multiple parameters, such as photosynthetic light capture and attenuation, nutrient uptake, photobioreactor hydrodynamics and gas-liquid mass transfer. In order to optimize productivity while keeping a standard product quality, a permanent control of the main cultivation parameters is necessary, where the continuous cultivation has shown to be the best option. However it is of utmost importance to recognize the singularity of continuous cultivation of cyanobacteria and microalgae due to their dependence on light availability and intensity. In this sense, this review provides comprehensive information on recent breakthroughs and possible future trends regarding technological and process improvements in continuous cultivation systems of microalgae and cyanobacteria, that will directly affect cost-effectiveness and product quality standardization. An overview of the various applications, techniques and equipment (with special emphasis on photobioreactors) in continuous cultivation of microalgae and cyanobacteria are presented. Additionally, mathematical modelling, feasibility, economics as well as the applicability of continuous cultivation into large-scale operation, are discussed.This research work was supported by the grant SFRH/BPD/98694/2013 (Bruno Fernandes) from Fundacao para a Ciencia e a Tecnologia (Portugal). The authors thank the FCT Strategic Project PEst-OE/EQB/LA0023/2013. The authors also thank the Project "BioInd Biotechnology and Bioengineering for improved Industrial and Agro-Food processes, REF. NORTE-07-0124-FEDER-000028" Co-funded by the Programa Operacional Regional do Norte (ON.2-O Novo Norte), QREN, FEDE

The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus ¹³³Sb

The γ-ray decay of excited states of the one-valence-proton nucleus ¹³³Sb has been studied using cold-neutron induced fission of ²³⁵U and ²⁴¹Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between γ-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 μs isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr₃(Ce) scintillators, revealed a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus ¹³²Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin

Ultra-fast timing study of exotic neutron-rich Fe isotopes

The cornerstone of nuclear structure, as we know it from stable nuclei, is the existence of magic numbers. The most stable nuclei arise for completely occupied shells, closed shells, and give rise to the magic numbers. At the Valley of Stability their values are 8, 20, 28, 50, 82 and 126. The steady development of the production, separation and identication of exotic nuclei, together with the improvement of the detection techniques, makes it possible to experimentally explore nuclei further away from the Valley of Stability. These exotic nuclei with nucleon numbers supposed to be magic do not always have the properties one would expect. As extra nucleons are added (or removed) from stable nuclei, the single particle energies are modied and strong quadrupole correlations appear, which may neutralize the spherical meanfield shell gaps. The investigation of the evolution of shell structure far from stability has become a major subject in Nuclear Physics. Research in this field has strong implications also in nuclear astrophysics, because exotic nuclei have a crucial role in the processes of stellar nucleosynthesis leading to the formation of the nuclei present in the Universe. The IS474 experiment was performed at the ISOLDE facility, CERN, where $^{59-66}$Mn isotopes were created and their $\beta$-decay chains studied. In this PhD Thesis we focused on the study of the neutron-rich iron isotopes (odd-A $^{63;65}$Fe and even-A $^{66}$Fe) by means of gamma and Advanced Time-Delayed spectroscopy