Fukuchi  T.

Gono  Y.

Koike  T.

Ma  M.

Odahara  A.

Shinozuka  T.

Shirotori  K.

Suzuki  T.

Ukai  M.

Fukuchi, T.

Gono, Y.

Odahara, A.

Shinozuka, T.

Suzuki, T.

Ukai, M.

Koike, T.

Shirotori, K.

Ma, M.

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Study of High-Spin Structure in 151Er

紀要類 (bulletin)departmental bulletin pape

Tohoku University Repository (TOUR) / 東北大学機関リポジトリ

Study of High-Spin Structure in 151Er著者 Fukuchi  T., Gono  Y., Odahara  A., Shinozuka T., Suzuki  T., Ukai  M., Koike  T., Shirotori K., Ma  M.journal orpublication titleCYRIC annual reportvolume 2005page range 6-7year 2005URL http://hdl.handle.net/10097/50301CYRIC Annual Report 2005    I. 2.  Study of High-Spin Structure in 151Er    Fukuchi T.1, Gono Y.2, Odahara A.1, Shinozuka T.3, Suzuki T.3, Ukai M.3, Koike T.4, Shirotori K.4, and Ma Y.4 1Department of Physics, Osaka University 2RIKEN 3Cyclotron and Radioisotope Center, Tohoku University 4Department of Physics, Tohoku University    High-spin isomers were reported in N = 83 isotones systematically1), namely 143Nd, 144Pm, 145Sm, 146Eu, 147Gd, 148Tb, 149Dy, 150Ho and 151Er.  Their lifetimes range from 10 ns to a few μ sec.  The excitation energies of those isomers are close each other ranging between 8.5 and 9.0MeV except for 151Er.  Configuration of the high-spin isomers are deduced experimentally and theoretically2) to be [ν (f7/2h9/2i13/2) π (h11/22)]49/2+ for odd nuclei and [ν (f7/2h9/2i13/2) π (d5/2-1h11/22)]27+ for odd-odd nuclei.  In a high-spin region of these nuclei, the angular momenta of individual valence particles align to the symmetry axis so that the overlaps of nucleon wave functions become to be maximum.  Then the shape changes from near spherical to oblate.  According to the Deformed Independent Particle Model (DIPM) calculations2), the shapes suddenly change at high-spin isomeric states.  This sudden shape change causes the high-spin isomer.  Therefore, these isomers could be described as high-spin shape isomers. As to 151Er nucleus, Jπ = 67- isomer at 10.6MeV was reported by C. Foin et al.3,4).  It is important to investigate the high-spin isomer in 151Er, since the spin-parity and the excitation energy of the high-spin isomer in this nuclei are largely different to those of other isotones. An experiment for 151Er was performed at Cyclotron and Radioisotope Center (CYRIC), Tohoku University.  Excitation states in 151Er were populated using the reaction 116Sn(40Ar,5n)151Er.  The 116Sn target of 1.4 mg/cm2 was enriched to 90% and a target foil was backed by 11mg/cm2 lead to stop the reaction products.  This target was bombarded by 40Ar beam of 197MeV with intensity of around 2pnA provided by the cyclotron.  A germanium ball, Hyperball-2, which consist of 12 single and 4 clover type detectors was  6used for prompt and delayed γ-γ-γ coincidence measurements.  The total detection efficiency was about 3.2% for 1.3-MeV γ-ray in the singles mode.  A total of 4.5×108 above 3-fold coincidence events were recorded in event by event mode.  An example of the γ-ray spectrum obtained by gating on the 1100-keV transition which belongs to 151Er is shown in Fig.1.  The coincidence relations between transitions are determined by this kind of spectrum.  In order to determine the spin-parity of the high-spin isomer in 151Er, analyses of γ-ray angular correlations and γ-ray linear polarization are also performing.  The detailed analyses are now in progress.   References  1) Gono Y., et al., Eur. Phys. J. A 13 (2002) 5 and references therein. 2) Dossing T., et al., Phys. Scr. 24 (1981) 258. 3) Foin C., et al., Eur. Phys. J. A 8 (2000) 451. 4) Andre A., et al., Z. Phys. A 337 (1990) 349.       116 134163216289364378416554575777100210111140895 0 1000 2000 3000 4000 5000 0  200  400  600  800  1000  1200Counts/ChannelGamma-ray energy (keV)   Figure 1.  Gamma-ray spectrum obtained by gating on the 1100-keV γ-ray in 151Er.  Transitions in 151Er are labeled in energy.  7

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Study of High-Spin Structure in 151Er

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