150 research outputs found
Conversion coefficients and band assignments in Ta-180
The conversion coefficients for several bandhead decays in Ta-180 have been measured using pulsed-beam techniques and the Yb-176(Li-7,3n)Ta-180 reaction. The spin and parity of the 520 keV Intrinsic state is established as 4(+) and several earlier assignments are confirmed. Two-quasiparticle configurations for the 520 and 592 keV states are discussed and following reanalysis of the band properties, a consistent interpretation is reached. The 520 keV 4(+) state is associated with the favored coupling of the nu 1/2(-)[521]x pi 9/2(-)[514] configuration while the 592 keV (5(+)) state is identified with the nu 1/2(-)[510]x pi 9/2(-)[514] configuration
K-Pi=6+ and 8- isomer decays in HF-172 and DELTA-K=8 E1 transition rates
A recoil-shadow measurement of isomer decay in 172Hf has revealed many weak gamma-ray transitions. One of these is a sevenfold K-forbidden E1 transition from the K(pi) = 8- isomer (T1/2 = 163 ns) to the K(pi) = 0+ ground-state band. The low hindrance factor for this transition in Hf-172 is compared with the hindrance factors for other DELTAK = 8 E1 transitions
Internal Conversion Coefficients - How Good Are They Now?
Internal conversion coefficients involving atomic electrons (ICC) and electron-positron pairs (IPC) are often required to determine transition multipolarities and total transition rates. A new internal conversion coefficient data base, BrIcc has been developed which integrates a number of tabulations on ICC and IPC, as well as {Omega}(E0) electronic factors. To decide which theoretical internal conversion coefficient table to use, the accurately determined experimental {alpha}{sub K}, {alpha}{sub L}, {alpha}{sub Total} and {alpha}{sub K}/{alpha}{sub L} values were compared with the new Dirac-Fock calculations using extreme assumptions on the effect of the atomic vacancy. While the overall difference between experiment and theory is less than 1%, our analysis shows preference towards the so called ''Frozen Orbital'' approximation, which takes into account the effect of the atomic vacancy
Resolution of the w-179-isomer anomaly: exposure of a Fermi-aligned s-band
The K-pi = 35-/2, five-quasiparticle isomer in W-179 is shown to decay into the region of a backbend in the 7-/2[514] band, allowing for the first time the identification of a full set of aligned-band states. Destructive interference results from level mixing in the band-crossing region. The deduced gamma-ray branching ratios are used to establish the mixing matrix elements and to show that the aligned band has a high value of the K quantum number. The properties of well-defined alignment and yet also high K provide the first clear example of a Fermi-aligned s band. The anomalous decay of the isomer itself is now explained
Anomalous isomeric decays in 174Lu as a probe of K-mixing and interactions in deformed nuclei
A Kπ=13+, 280 ns four-quasiparticle isomer in the odd-odd nucleus 174Lu has been identified and characterized. The isomer decays to both Kπ=7+ and Kπ=0+ rotational bands obtained from the parallel and antiparallel coupling of the proton 7/2+[404] and neutron 7/2+[633] orbitals. K mixing caused by particle-rotation coupling explains the anomalously fast transition rates to the 7+ band but those to the 0+ band are caused by a chance degeneracy between the isomer and a collective state, allowing the mixing matrix element for a large K difference to be deduced
Hindrance of the excitation of the Hoyle state and the ghost of the state in C
While the Hoyle state (the isoscalar excitation at 7.65 MeV in
C) has been observed in almost all the electron and inelastic
scattering experiments, the second excited state of C at MeV, believed to be an excitation of the Hoyle state, has not
been clearly observed in these measurements excepting the high-precision \aap
experiments at and 386 MeV. Given the (spin and isospin zero)
-particle as a good probe for the nuclear isoscalar excitations, it
remains a puzzle why the peak of the state could not be clearly
identified in the measured \aap spectra. To investigate this effect, we have
performed a microscopic folding model analysis of the \ac scattering data at
240 and 386 MeV in both the Distorted Wave Born Approximation (DWBA) and
coupled-channel (CC) formalism, using the nuclear transition densities given by
the antisymmetrized molecular dynamics (AMD) approach and a complex CDM3Y6
density dependent interaction. Although AMD predicts a very weak transition
strength for the direct excitation, our detailed analysis
has shown evidence that a weak \emph{ghost} of the state could be
identified in the 240 MeV \aap data for the state at 10.3 MeV, when the
CC effects by the indirect excitation of the state are taken into
account. Based on the same AMD structure input and preliminary \aap data at 386
MeV, we have estimated relative contributions from the and
states to the excitation of C at MeV as well as
possible contamination by state.Comment: Accepted for publication in Phys. Lett.
Study of refractive structure in the inelastic 16O+16O scattering at the incident energies of 250 to 1120 MeV
The data of inelastic 16O+16O scattering to the lowest 2+ and 3- excited
states of 16O have been measured at Elab = 250, 350, 480, 704 and 1120 MeV and
analyzed consistently in the distorted wave Born approximation (DWBA), using
the semi- microscopic optical potentials and inelastic form factors given by
the folding model, to reveal possible refractive structure of the nuclear
rainbow that was identified earlier in the elastic 16O+16O scattering channel
at the same energies. Given the known transition strengths of the 2+ and 3-
states of 16O well determined from the (e,e') data, the DWBA description of the
inelastic data over the whole angular range was possible only if the absorption
in the exit channels is significantly increased (especially, for the
16O+16O(2+) exit channel). Although the refractive pattern of the inelastic
16O+16O scattering was found to be less pronounced compared to that observed in
the elastic scattering channel, a clear remnant of the main rainbow maximum
could still be seen in the inelastic cross section at Elab = 350 - 704 MeV.Comment: 26 pages, 10 figures, Accepted for publication in Nucl. Phys.
Spherical and deformed isomers in Pb-188
Several isomers in Pb-188 have been identified using pulsed beams, the recoil-shadow technique, and the Er-164(Si-28,4n) Pb-188 reaction. Two of the isomers feed the 10(+) state of the yrast sequence and are suggested to be the 11(-) and 12(+) states from oblate and spherical configurations, respectively. The 12(+) isomer is fed weakly by another isomer with a relatively long lifetime, but it has not been characterized. A fourth isomer with a lifetime of about 1.2 mu s leads via a complicated path to the 8(+) and lower spin yrast states. It is a candidate for the K-pi = 8(-), two-quasineutron state which occurs systematically in N = 106 prolate-deformed nuclei, supporting the assumption that the intruding collective well is prolate
Microscopic study of the isoscalar giant resonances in 208Pb induced by inelastic alpha scattering
The energetic beam of (spin and isospin zero) -particles remains a
very efficient probe for the nuclear isoscalar giant resonances. In the present
work, a microscopic folding model study of the isoscalar giant resonances in
Pb induced by inelastic \aPb scattering at and 386
MeV has been performed using the (complex) CDM3Y6 interaction and nuclear
transition densities given by both the collective model and Random Phase
Approximation (RPA) approach. The fractions of energy weighted sum rule around
the main peaks of the isoscalar monopole, dipole and quadrupole giant
resonances were probed in the Distorted Wave Born Approximation analysis of
inelastic \aPb scattering using the double-folded form factors given by
different choices of the nuclear transition densities. The energy distribution
of the and strengths given by the multipole decomposition
{analyses} of the \aap data under study are compared with those predicted by
the RPA calculation.Comment: Accepted for publication in Nuclear Physics
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