Ultrahigh-resolution γ-ray spectroscopy of 156Gd: a test of tetrahedral symmetry.

Tetrahedral symmetry in strongly interacting systems would establish a new class of quantum effects at subatomic scale. Excited states in 156Gd that could carry the information about the tetrahedral symmetry were populated in the 155Gd(n,γ)156Gd reaction and studied using the GAMS4/5 Bragg spectrometers at the Institut Laue-Langevin. We have identified the 5(1)- → 3(1)- transition of 131.983(12) keV in 156Gd and determined its intensity to be 1.9(3)x10(-6) per neutron capture. The lifetime τ=220(-30)(+180) fs of the 5(1)- state in 156Gd has been measured using the GRID technique. The resulting B(E2)=293(-134)(+6) Weisskopf unit rate of the 131.983 keV transition provides the intrinsic quadrupole moment of the 5(1)- state in 156Gd to be Q0=7.1(-1.6)(+0.7) b. This large value, comparable to the quadrupole moment of the ground state in 156Gd, gives strong evidence against tetrahedral symmetry in the lowest odd-spin, negative-parity band of 156Gd.

[1]  A. Gózdz,et al.  Mean-field theory of nuclear stability and exotic point-group symmetries , 2010 .

[2]  A. Gózdz,et al.  MODELING THE ELECTROMAGNETIC TRANSITIONS IN TETRAHEDRAL-SYMMETRIC NUCLEI , 2010 .

[3]  Z. Podolyák,et al.  Spectroscopy of neutron-rich {sup 168,170}Dy: Yrast band evolution close to the N{sub p}N{sub n} valence maximum , 2010 .

[4]  J. Sharpey-Schafer,et al.  Nonzero quadrupole moments of candidate tetrahedral bands. , 2010, Physical review letters.

[5]  N. Schunck,et al.  Search for Fingerprints of Tetrahedral Symmetry in 156 Gd , 2008, 0811.1283.

[6]  N. Schunck,et al.  Island of rare Earth nuclei with tetrahedral and octahedral symmetries: possible experimental evidence. , 2006, Physical review letters.

[7]  M. Cromaz,et al.  E2 transitions between positive- and negative-parity states of the ground-state alternating-parity bands , 2005 .

[8]  N. Schunck,et al.  Nuclear tetrahedral symmetry: possibly present throughout the periodic table. , 2002, Physical review letters.

[9]  J. Katakura,et al.  Rotational bands of Gd , 2001 .

[10]  E. Kessler,et al.  The GAMS4 flat crystal facility , 2001 .

[11]  H. Lehmann,et al.  The GRID Technique: Current Status and New Trends , 2000, Journal of research of the National Institute of Standards and Technology.

[12]  M. Jentschel,et al.  Ultrahigh resolution study of collective modes in {sup 158}Gd , 1999 .

[13]  Zamfir,et al.  Systematic behavior of octupole states in deformed rare earth nuclei and the interacting boson approximation. , 1996, Physical review. C, Nuclear physics.

[14]  H. Börner,et al.  Nuclear structure of 156Gd studied with (n, γ), (n, e−), (d, p), (d, t) reactions and lifetime measurements , 1993 .

[15]  J. Jolie,et al.  Sub-picosecond lifetime measurements by gamma ray induced Doppler broadening , 1993 .

[16]  A. Krämer-Flecken,et al.  Evidence for coexistence of reflection asymmetric and symmetric shapes in 150Sm , 1987 .

[17]  W. T. Milner,et al.  Transition probability, B(E2)up-arrow, from the ground to the first-excited 2/sup +/ state of even-even nuclides , 1987 .

[18]  Holzmann,et al.  Octupole deformation in neutron-rich barium isotopes. , 1986, Physical review letters.

[19]  D. Chmielewska,et al.  Nuclear data sheets for A = 99 , 1986 .

[20]  W. Nazarewicz,et al.  A new region of intrinsic reflection asymmetry in nuclei around 145Ba , 1985 .

[21]  D. Frenne,et al.  Nuclear data sheets for A = 110 , 1983 .

[22]  O. Scholten,et al.  The level structure of 156Gd studied by means of the (α, 2nγ) reaction , 1981 .

[23]  W. H. Kelly,et al.  Nuclear data sheets for A = 101 , 1973 .