K-isomerism and γ-softness

doi:10.1016/0375-9474(89)90698-2

Nuclear Physics A

Volume 491, Issue 2, 9 January 1989, Pages 179-204

https://doi.org/10.1016/0375-9474(89)90698-2 Get rights and content

Abstract

The decay rates from K^π = 10⁺ isomers into the ground-band states for ¹⁸²W and ¹⁸⁴Os are calculated by employing a particle-plus-γ-soft-rotor model and a particle-plus-triaxial-rotor model. As for the description of the degree of freedom of axial asymmetry, Bohr's model of γ-vibration around γ = 0 and Davydov's model of statically deformed triaxial rotor are shown to give clearly distinct results about the degree of violation of the K-selection rule, although they give similar values for quantities of collective character. This result implies a possibility to obtain information about the size of the quantum fluctuation in γ from the decay rates of K-isomers, using the knowledge of the mean value of γ determined from quantities of collective character.

References (37)

A. Bohr
C. Baktash et al.
Phys. Rev.
(1980)
A. Hayashi et al.
Phys. Rev. Lett.
(1984)
J. Pedersen et al.
Phys. Rev. Lett.
(1985)
N. Tajima et al.
Phys. Lett.
(1986)
T. Suzuki et al.
Nucl. Phys.
(1977)
A. Schuh et al.
Nucl. Phys.
(1984)
N. Onishi et al.
Nucl. Phys.
(1986)
R.J. Turner et al.
Nucl. Phys.
(1973)
G. Rakavy
Nucl. Phys.
(1957)

A. Ikeda et al.

Phys. Lett.

(1979)

F. Grümmer et al.

Nucl. Phys.

(1979)

F. Grümmer et al.

Nucl. Phys.

(1979)

M. Baranger et al.

Nucl. Phys.

(1968)

A. Ikeda et al.

Prog. Theor. Phys.

(1983)

J. Almberger et al.

Nucl. Phys.

(1980)

Phys. Scripta

(1980)

R.R. Whitehead et al.

Computational methods for shell model calculations

A. Bohr

Mat. Fys. Medd. Dan. Vid. Selsk.

(1952)

A. Bohr et al.

Mat. Fys. Medd. Dan. Vid. Selsk.

(1953)

A.S. Davydov et al.

Nucl. Phys.

(1958)

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Nuclear Data Sheets for A = 182
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Nuclear spectroscopic information for known nuclides of mass number 182 (Yb,Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au, Hg,Tl,Pb) with Z=70 to 82 and N=112 to 100 have been evaluated and presented together with adopted energies and Jπ of levels in these nuclei. No excited state data are yet available for ¹⁸²Y and ¹⁸²Lu, while only limited structure information is available for ¹⁸²Pb and ¹⁸²Tl. Rotational band structures are known for ¹⁸²Hg and ¹⁸²Au but spin–parity assignments remain largely tentative. The decays of ¹⁸²Lu, ¹⁸²Hg, ¹⁸²Au and ¹⁸²Tl are not well established. The ¹⁸²Hf isotope is of geophysical and astrophysical interest.
This evaluation supersedes previous full evaluations of A = 182 published by 2010Si13, 1988Fi05 and 1975Sc13, and a selected (mainly high–spin) update of A = 182 published by 1995Si04.
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Roles of triaxiality and residual interaction in signature inversions of A ∼ 130 odd-odd nuclei
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K-isomerism and γ-softness

Abstract

Phys. Rev.

Phys. Rev. Lett.

Phys. Rev. Lett.

Phys. Lett.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Phys. Lett.

Nucl. Phys.

Nucl. Phys.

Nucl. Phys.

Prog. Theor. Phys.

Nucl. Phys.

Phys. Scripta

Mat. Fys. Medd. Dan. Vid. Selsk.

Mat. Fys. Medd. Dan. Vid. Selsk.

Nucl. Phys.