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Title: Nuclear isomers: structures and applications

Abstract

Isomeric states in the nuclei along the rapid proton capture process path are studied by the projected shell model. Emphasis is given to two waiting point nuclei 68Se and 72Kr that are characterized by shape coexistence. Energy surface calculations indicate that the ground state of these nuclei corresponds to an oblate-deformed minimum, while the lowest state at the prolate-deformed minimum can be considered as a shape isomer. Due to occupation of the orbitals with large K-components, states built upon two-quasiparticle excitations at the oblate-deformed minimum may form high K-isomers. The impact of the isomer states on isotopic abundance in X-ray bursts is studied in a multi-mass-zone X-ray burst model by assuming an upper-lower limit approach.

Authors:
; ; ;  [1];  [2]
  1. Department of Physics, University of Notre Dame, Notre Dame, Indiana 46545 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20798287
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 819; Journal Issue: 1; Conference: 12. international symposium on capture gamma-ray spectroscopy and related topics, Notre Dame, IN (United States), 4-9 Sep 2005; Other Information: DOI: 10.1063/1.2187858; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CAPTURE; COSMIC X-RAY BURSTS; ELEMENT ABUNDANCE; EXCITATION; GROUND STATES; ISOMERIC NUCLEI; KRYPTON 72; PROTONS; SELENIUM 68; SHELL MODELS; X RADIATION

Citation Formats

Sun Yang, Wiescher, Michael, Aprahamian, Ani, Fisker, Jacob, and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46545. Nuclear isomers: structures and applications. United States: N. p., 2006. Web. doi:10.1063/1.2187858.
Sun Yang, Wiescher, Michael, Aprahamian, Ani, Fisker, Jacob, & Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46545. Nuclear isomers: structures and applications. United States. doi:10.1063/1.2187858.
Sun Yang, Wiescher, Michael, Aprahamian, Ani, Fisker, Jacob, and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46545. Mon . "Nuclear isomers: structures and applications". United States. doi:10.1063/1.2187858.
@article{osti_20798287,
title = {Nuclear isomers: structures and applications},
author = {Sun Yang and Wiescher, Michael and Aprahamian, Ani and Fisker, Jacob and Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46545},
abstractNote = {Isomeric states in the nuclei along the rapid proton capture process path are studied by the projected shell model. Emphasis is given to two waiting point nuclei 68Se and 72Kr that are characterized by shape coexistence. Energy surface calculations indicate that the ground state of these nuclei corresponds to an oblate-deformed minimum, while the lowest state at the prolate-deformed minimum can be considered as a shape isomer. Due to occupation of the orbitals with large K-components, states built upon two-quasiparticle excitations at the oblate-deformed minimum may form high K-isomers. The impact of the isomer states on isotopic abundance in X-ray bursts is studied in a multi-mass-zone X-ray burst model by assuming an upper-lower limit approach.},
doi = {10.1063/1.2187858},
journal = {AIP Conference Proceedings},
number = 1,
volume = 819,
place = {United States},
year = {Mon Mar 13 00:00:00 EST 2006},
month = {Mon Mar 13 00:00:00 EST 2006}
}
  • Nuclear K-isomers play a pivotal role in understanding the structure of deformed, axially symmetric nuclei. Examples are presented of recent studies of exotic multi-quasiparticle isomers in the A{approx}180 rare-earth region at the extreme of angular momentum and neutron number. A specific band-mixing scenario is invoked to explain the unusual decay path of the K{pi}=57/2- isomer (T1/2=22 ns) in 175Hf, the highest spin K-isomer known in nature. The discovery of a suite of high-K isomers, above the previously known K{pi}=23/2- (T1/2=160 d) state in 177Lu, using deep-inelastic and multi-nucleon transfer reactions is discussed.
  • Excited states in the doubly odd nucleus {sup 80}Rb have mainly been studied via the {sup 68}Zn({sup 19}F,{alpha}3{ital n}) reaction at 72 MeV beam energy utilizing the NORDBALL detector system. The level scheme has been extended up to a (15{sup +}) state at 4446 keV excitation energy. In the low-spin region seven new isomers with lifetimes in the nanosecond region have been found. In addition, a 6{sup +} isomer with a half-life of the order of {mu}s has been identified at an excitation energy of 494.4 keV. For the level sequence built on this isomer positive parity is suggested andmore » the states are ascribed to the intruder two-quasiparticle configuration ({pi}{ital g}{sub 9/2}{direct product}{nu}{ital g}{sub 9/2}) and collective excitations.« less
  • The structure and energies of several alternative isomeric structures of C{sub 60} spheroids have been computed with semiempirical (MNDO) and ab initio Hartree-Fock molecular orbital techniques. Unlike the ideal icosahedral structure, these isomers are characterized by the presence of two or more pairs of adjacent pentagonal rings. The energy contributions of these adjacent pentagonal defects are roughly additive, with each defect making the structure less stable by {approx_equal} 1 eV. The lowest energy alternative isomer of C{sub 60} has C{sub 2v} symmetry and lies {approx_equal} 2 eV higher in energy than the icosahedral ground-state structure. 23 refs., 7 figs., 1more » tab.« less
  • The various isomers including stable structures, carbenes, and diradicals on the C{sub 3}H{sub 4} surface have been investigated. The two carbenes propenylidene and cyclopropylidene have been found to have singlet ground states. Vinylmethylene is predicted to have a triplet ground state with a planar diradical type of structure. The syn and anti forms of this state are degenerate. This is in agreement with the observation of two triplet states in the electron spin resonance (ESR) spectra. The {pi} electrons are found to be delocalized over the three carbons. The singlet diradical structures are found to be more stable than themore » carbene structures, which retain the CH{sub 2} = CH allylic structures. The orbital compositions of the frontier orbitals of all systems have been determined to examine the nature of these orbitals.« less
  • The B9- cluster was found previously to be an unprecedented molecular wheel containing an octacoordinate planar boron with D8h symmetry in a combined photoelectron spectroscopy (PES) and theoretical study [H. J. Zhai et al., Angew. Chem. Int. Ed. 42, 6004 (2003)]. However, the PES spectra of B9- exhibit minor features that cannot be explained by the global minimum D8h structure, suggesting possible contributions from low-lying isomers at finite temperatures. Here we present Car-Parrinello molecular dynamics with simulated annealing simulations to fully explore the potential energy surface of B9- and search for low-lying isomers that may account for the minor PESmore » features. We performed density functional theory (DFT) calculations with different exchange-correlation functionals and ab initio calculations at various levels of theory with different basis sets. Two three-dimensional low-lying isomers were found, both of Cs symmetry, 6.29 (Cs-2) and 10.23 (Cs-1) kcal/mol higher in energy than the D8h structure at the highest CCSD(T) level of theory. Calculated detachment transitions from the Cs-2 isomer are in excellent agreement with the minor features observed in the PES spectra of B9-. The B9- cluster proves to be a challenge for most DFT methods and the calculated relative energies strongly depend on the exchange-correlation functionals, providing an excellent example for evaluating the accuracies of various DFT methods.« less