Coincidencias ultrarrápidas con matrices de LaBr₃(Ce) : optimización de detectores y aplicación al núcleo ¹³⁶Te

Tesis de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Estructura de la Materia, Física Térmica y Electrónica, leída el 10-12-2018Nuclei with few valence particles outside of a doubly-magic core provide valuable information about single-particle energies, nucleon-nucleon e_ective interactions and may give insight into the onset of collectivity. The region around 132Sn draws particular attention because of the unexpected modi_cations of the shell structure and the sudden collective behaviour that arises. The 136Te nucleus, with two protons and two neutrons coupled to the doubly-magic 132Sn (Z=50 and N=82) constitutes an excellent testing ground for the study of these phenomena, and so it is studied in this PhD thesis. One of the best means to study exotic nuclei is through lifetime measurements of excited states since they allow direct and model independent access to electromagnetic transition probabilities, which are key quantities for the study of single-particle configurations, nuclear collectivity, and make it possible to test theoretical models. Thus this PhD thesis investigates the 136Te nucleus through the lifetime measurements of its excited states...El estudio de núcleos con unos pocos nucleones de valencia fuera de la estructura de un núcleo doblemente mágico proporciona información muy relevante sobre los estados de partícula independiente, sobre las interacciones entre nucleones, y puede ayudar a comprender el comportamiento colectivo. Debido a las modificaciones que aparecen en la estructura de capas y los comportamientos colectivos observados en la región cercana al doblemente mágico 132Sn, el núcleo 136Te atrae gran interés, siendo un caso representativo para el estudio de estos fenómenos, ya que cuenta con dos protones y dos neutrones acoplados al 132Sn (Z=50 and N=82), por ende es estudiado en esta tesis. Una de las mejores maneras para estudiar estas características es la medida de las vidas medias de estados nucleares excitados, ya que permiten el acceso directo a las probabilidades de transición electromagnética, que son magnitudes clave en la física nuclear. Las probabilidades reducidas de transición son especialmente adecuadas para obtener información sobre configuraciones de partícula independiente, sobre efectos colectivos y configuraciones deformadas, además de permitir poner a prueba los modelos teóricos. Los tiempos de vida de estados excitados son observables directos que pueden ser medidos con buena precisión, lo que nos permite obtener probabilidades de transición independientes de modelo...Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

Search for the ⁷³Gaground-state doublet splitting in the β decay of ⁷³Zn

The existence of two close-lying nuclear states in ⁷³Ga has recently been experimentally determined: a 1/2⁻ spin-parity for the ground state was measured in a laser spectroscopy experiment, while a J_π = 3/2⁻ level was observed in transfer reactions. This scenario is supported by Coulomb excitation studies, which set a limit for the energy splitting of 0.8 keV. In this work, we report on the study of the excited structure of ⁷³Ga populated in the β decay of ⁷³Zn produced at ISOLDE, CERN. Using β-gated, γ-ray singles, and γ –γ coincidences, we have searched for energy differences to try to delimit the ground-state energy splitting, providing a more stringent energy difference limit. Three new half-lives of excited states in ⁷³Ga have been measured using the fast-timing ;method with LaBr₃(Ce) detectors. From our study, we help clarify the excited structure of ⁷³G and we extend the existing ⁷³Zn decay to ⁷³Ga with 8 new energy levels and 35 γ transitions. We observe a 195-keV transition consistent with a γ ray de-exciting a short-lived state in the β-decay parent ⁷³Zn

TAGS measurements of ¹⁰⁰Nb ground and isomeric states and 140¹⁴⁰Cs for neutrino physics with the new DTAS detector

In this work we report on total absorption γ-ray spectroscopy measurements of the β decay of fission products that are important contributors to the antineutrino spectrum. The experiment was performed at IGISOL as a part of a campaign of measurements with the new DTAS spectrometer. Preliminary results of the analysis of the β decay of ¹⁰⁰Nb, ¹⁰⁰Nb and ¹⁴⁰Cs are presented

Total absorption studies of high priority decays for reactor applications: ⁸⁶Br and ⁹¹Rb

Preliminary results from beta decay studies of nuclei that are important for reactor applications are presented. The beta decays have been studied using the total absorption technique (TAS) and the pure beams provided by the JYFLTRAP system at the IGISOL facility of the University of Jyvaskyla

Experimental study of Tc-100 beta decay with total absorption gamma-ray spectroscopy

The beta decay of Tc-100 has been studied by using the total absorption gamma-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility in Jyvaskyla. In this work the new Decay Total Absorption gamma-ray Spectrometer in coincidence with a cylindrical plastic beta detector has been employed. The beta intensity to the ground state obtained from the analysis is in good agreement with previous high-resolution measurements. However, differences in the feeding to the first-excited state as well as weak feeding to a new level at high excitation energy have been deduced from this experiment. Theoretical calculations performed in the quasiparticle random-phase approximation framework are also reported. Comparison of these calculations with our measurement serves as a benchmark for calculations of the double beta decay of Mo-100

Total absorption spectroscopy of fission fragments relevant for reactor antineutrino spectra

The accurate determination of reactor antineutrino spectra remains a very active research topic for which new methods of study have emerged in recent years. Indeed, following the long-recognized reactor anomaly (measured antineutrino deficit in short baseline reactor experiments when compared with spectral predictions), the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have recently demonstrated the existence of spectral distortions in their measurements with respect to the same predictions. These spectral predictions were obtained through the conversion of integral beta-energy spectra obtained at the ILL research reactor. Several studies have shown that the underlying nuclear physics required for the conversion of these spectra into antineutrino spectra is not totally understood. An alternative to such converted spectra is a complementary approach that consists of determining the antineutrino spectrum by means of the measurement and processing of nuclear data. The beta properties of some key fission products suffer from the pandemonium effect which can be circumvented by the use of the Total Absorption Gammaray Spectroscopy technique (TAGS). The two main contributors to the Pressurized Water Reactor antineutrino spectrum in the region where the spectral distortion has been observed are ⁹²Rb and ¹⁴²Cs, which have been measured at the radioactive beam facility of the University of Jyväskylä in two TAGS experiments. We present the results of the analysis of the TAGS measurements of the β-decay properties of ⁹²Rb along with preliminary results on ¹⁴²Cs and report on the measurements already performed

Summation Calculations for Reactor Antineutrino Spectra, Decay Heat and Delayed Neutron Fractions Involving New TAGS Data and Evaluated Databases

Three observables of interest for present and future reactors depend on the beta decay properties of the fission products: antineutrinos from reactors, the reactor decay heat and delayed neutron emission. In these proceedings, we present new results from summation calculations of the first two quantities quoted above, performed with evolved independent yields coupled with fission product decay data, from various nuclear data bases or models. New TAGS results from the latest experiment of the TAGS collaboration at the JYFL facility of Jyvaskyla will be displayed as well as their impact on the antineutrino spectra and the decay heat associated to fission pulses of the main actinides

(208)po populated through EC/beta(+) decay

The structure of Po-208 resulting from the EC/beta(+) decay of At-208 was studied at CERN's ISOLDE Decay Station (IDS). The high statistics afforded by the high yield of At-208 and the high efficiency HPGe clusters at the IDS allowed for greater insight into lower intensity transitions and thus significant expansion of the Po-208 level scheme. Furthermore, investigation into the isomeric state yielded a new half life 377(9) ns in addition to uncovering new transitions populating the state

Fast timing measurement using an LaBr3 (Ce) scintillator detector array coupled with gammasphere

A fast-timing experiment was performed at the Argonne National Laboratory in December 2015 and January 2016, measuring decay radiation of fission products from a Cf-252 fission source. Details of the set-up, integration with Digital Gammasphere, and the data acquisition system are presented. The timing performance of the set-up, capable of measuring lifetimes from the nanosecond region down to tens of picoseconds, is discussed. First preliminary results from the fast-timing analysis of the fission fragment data are presented

Search for beta-delayed proton emission from Be-11

We report on an attempt to reproduce the observation of beta(-)-delayed proton emission from Be-11 through detection of the final state nucleus Be-10 with accelerator mass spectrometry. Twelve samples were collected at the ISOLDE facility at CERN at different separator settings, allowing tests of different sources of contamination to be carried out. The observed amounts of Be-10 per collected Be-11 rule out several contamination sources, but do not agree internally. Formation of BeH molecular ions in the ion source may explain our data, in which case an upper limit of the beta p branching ratio of 2.2 x 10(-6) can be derived