Elsevier

Nuclear Physics A

Volume 380, Issue 2, 24 May 1982, Pages 189-260
Nuclear Physics A

Levels in 156Gd studied in the (n, γ) reaction

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Abstract

Levels up to 2.3 MeV in 156Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in 156Gd was measured as Sn = 8535.8 ± 0.5 keV.

About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0+ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1+ bands at 1966, 2027 and 2187 keV; 2+ bands at 1154 (γ-band) and 1828 keV; and 4+ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1), 1366 keV (0), 1780 keV (2) and 2045 keV (4). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0+ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.

The lowest three negative-parity (octupole) bands of which the 0 and the 1 bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0+ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2+2, 4+1 and 21 bands.

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  • Cited by (0)

    Present address: Tandem Accelerator Laboratory, Box 533, Uppsala, Sweden.

    ∗∗

    Work supported by the US Department of Energy under DOE Contract no. DE-AC07-76IDO 1570.

    ∗∗∗∗

    Present address: Zentrum für Klinische Grundlagen-Forschung, Universität Ulm, 73 Ulm, Germany.

    ∗∗∗

    Present address: Institu für Kernphysic, Kernforschungsanlage Jülich, 517 Jülich, Germany.

    ∗∗∗∗∗

    Present address: Institut Laue-Langevin, 38042 Grenoble Cedex, France

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