ESTUDIOS DE ESTRUCTURA NUCLEAR USANDO COINCIDENCIAS γ-PARTICULA: PRESENTE Y FUTURO.

El método de selección de canales de reacción en espectroscopía de rayos γ ha sido clave en los estudios de estructura nuclear para núcleos lejos del valle de estabilidad β. Ejemplos de tales experimentos en ambos lados del valle de estabilidad son discutidos y se presentan algunos de los arreglos experimentales típicos: Gammasphere y Gretina, con detectores de Germanio hiperpuro, incluyendo un conjunto de detectores de partículas. Se presentan el uso de haces de iones estables y radioactivos, así como las perspectivas históricas de la estructura nuclear que han buscado la consistencia, desde los núcleos ricos en protones hasta los ricos en neutrones.Reaction-channel γ -ray spectroscopy is a key method in nuclear-structure studies far from the β-stability valley. Examples of such experiments on both sides of the valley are discussed and some of the typical detector setups are introduced: the HPGe arrays Gammasphere and Gretina and the available suite of associated particle detectors. The use of stable and radioactive ion beams is covered (to some extend) as well. A sort of historical perspective is presented stating that the emphasis in nuclear-structure studies has shifted from proton-rich to neutron-rich nuclei

Complementary Mass Spectral Analysis of Isomeric O-bearing Organic Compounds and Fragmentation Differences through Analog Techniques for Spaceborne Mass Spectrometers

Mass spectrometers on board spacecraft typically use either impact ionization or electron ionization (EI) as ion sources. Understanding the similarities and differences in the spectral signatures and fragmentation patterns produced by different techniques in mass spectrometry could elucidate the composition of organic compounds. Here we present a comparison between the mass spectra obtained through laser-induced liquid beam ion desorption (LILBID; proven to simulate the impact ionization mass spectra of ice grains) and EI mass spectra of pairs of low-mass, isomeric aldehydes and ketones. Our comparison confirms that EI produces more fragmentation of carbonyl compounds, particularly aldehydes, than LILBID. We find protonated molecular ions [M+H]+ in LILBID but molecular ions [M]+ in EI spectra. From the evaluated species, LILBID generally produces oxygen-carrying fragment ions (e.g., [CHO]+ and [C2H3O]+) in the mass ranges 26–30 and 39–44 u, while in EI, most ions in these ranges correspond to hydrocarbon fragments. The LILBID spectra additionally show mostly protonated oxygen-bearing fragments [CH3O]+ and [C2H5O]+ at m/z 31 and 45, less commonly observed in EI spectra. We observe a decrease in the relative intensities of cation fragment mass lines between m/z 26 and 33 and an increase between m/z 39 and 45, with an increasing carbon number for ketones and aldehydes with LILBID and EI, respectively. Our study provides a basis for complementary compositional analysis to identify the structural properties of organic species in a space environment using different spaceborne mass spectrometers (e.g., SUrface Dust Analyzer and MAss Spectrometer for Planetary EXploration) on board NASA’s future Europa Clipper space mission

The multiplicity of shapes in Tl nuclei

The results of experiments on rotational bands in light Tl nuclei are used to indicate the richness of shape phenomena in the vicinity of a closed proton shell. Rotational bands associated with normal prolate and oblate shapes as well as with a superdeformed shape are observed. 34 refs., 4 figs

Lifetime Measurements in 120Xe

Lifetimes for the lowest three transitions in the nucleus $^{120}$Xe have been measured using the Recoil Distance Technique. Our data indicate that the lifetime for the $2_{1}^{+} \to 0_{1}^{+}$ transition is more than a factor of two lower than the previously adopted value and is in keeping with more recent measurements performed on this nucleus. The theoretical implications of this discrepancy and the possible reason for the erroneous earlier results are discussed. All measured lifetimes in $^{120}$Xe, as well as the systematics of the lifetimes of the 2$_{1}^{+}$ states in Xe isotopes, are compared with predictions of various models. The available data are best described by the Fermion Dynamic Symmetry Model (FDSM).Comment: 9 pages, RevTeX, 3 figures with Postscript file available on request at [email protected], [email protected]. Submitted to Phys. Rev.

The observation of long-range three-body Coloumb effects in the decay of 16Ne

The interaction of an $E/A$=57.6-MeV $^{17}$Ne beam with a Be target was used to populate levels in $^{16}$Ne following neutron knockout reactions. The decay of $^{16}$Ne states into the three-body $^{14}$O+$p$+$p$ continuum was observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products were measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous experiments, the intrinsic decay width of the $^{16}$Ne ground state was found to be narrow ($\Gamma<60$~keV), consistent with theoretical estimates.Comment: 6 pages, 5 figure

Neutron-proton interaction in rare-earth nuclei: Role of tensor force

We investigate the role of the tensor force in the description of doubly odd deformed nuclei within the framework of the particle-rotor model. We study the rare-earth nuclei 174Lu, 180Ta, 182Ta, and 188Re using a finite-range interaction, with and without tensor terms. Attention is focused on the lowest K=0 and K=1 bands, where the effects of the residual neutron-proton interaction are particularly evident. Comparison of the calculated results with experimental data evidences the importance of the tensor-force effects.Comment: 8 pages, 5 figures, to be published on Physical Review

Lifetime Measurements in 182,186^{182,186}Pt}

Lifetimes in the yrast bands of the nuclei $^{182,186}$Pt have been measured using the Doppler-shift Recoil Distance technique. The results in both cases {\em viz.} a sharp increase in B(E2) values at very low spins, may be interpreted as resulting from a mixing between two bands of different quadrupole deformations.Comment: 12 pages; 4 figures; submitted to PR

Description of Multi Quasi Particle Bands by the Tilted Axis Cranking Model

The selfconsistent cranking approach is extended to the case of rotation about an axis which is tilted with respect to the principal axes of the deformed potential (Tilted Axis Cranking). Expressions for the energies and the intra bands electromagnetic transition probabilities are given. The mean field solutions are interpreted in terms of quantal rotational states. The construction of the quasiparticle configurations and the elimination of spurious states is discussed. The application of the theory to high spin data is demonstrated by analyzing the multi quasiparticle bands in the nuclide-s with $N=102,103$ and $Z=71,72,73$.Comment: 23 pages 27 figure

ΔI=4\Delta I=4 and ΔI=8\Delta I=8 bifurcations in rotational bands of diatomic molecules

It is shown that the recently observed $\Delta I=4$ bifurcation seen in superdeformed nuclear bands is also occurring in rotational bands of diatomic molecules. In addition, signs of a $\Delta I=8$ bifurcation, of the same order of magnitude as the $\Delta I=4$ one, are observed both in superdeformed nuclear bands and rotational bands of diatomic molecules.Comment: LaTex twice, 10 pages and 5 PS figures provided upon demand by the Author