The data summarized here are from 15 different excitation modes: ¹⁵⁶Eu β^- decay; ¹⁵⁶Tb ε+β⁺ decay (5.35 d); ¹⁵⁵Gd(n,γ), with E_n=th, 1.9 keV and 58 keV; in-beam spectroscopy (¹⁵⁴Sm(α,2nγ)); ¹⁵⁶Gd(n,n’γ); (p,t); (t,p); (d,t); (d,p); Coul. ex.; ¹⁵⁶Gd(p,p’) and (d,d’); and ¹⁵⁶Gd(γ,γ’) and (e,e’). Other excitation modes given in this evaluation, but which did not yield data used here include: ¹⁵⁶Gd(μ,γ); and ¹⁵⁶Tb ε+β⁺ decay (5 h). Since these latter studies have no reported levels, they are not included in the Cross References. In addition, experimental and theoretical studies of the double-β decay of ¹⁵⁶Dy have recently appeared. These are referred to here, although they yield no new information regarding the ¹⁵⁶Gd levels.

¹⁵⁶Gd has been suggested to be an example of a proposed tetrahedral (Y₃^|+2) symmetry. 2010Je02, in (n,γ), find a 131.983 transition corresponding to energy difference between 5- and 3- levels, within uncertainty (as per an e-mail correspondence to the editors from Dominique Curien, co-author of 2010Je02), in the K^π=1- octupole band, suggesting that this is evidence against such a symmetry. 2010Do13 call this conclusion into question, citing studies suggesting that other effects might be present which could account for this transition.

Because of the way in which the (n,n’γ) and (e,e’) data are shown in the respective studies, a number of levels that are actually populated there may not be included in the appropriate Cross Reference listing. See the comments in these two data sets.

Levels: Levels populated by primary γ-ray transitions following thermal-neutron capture for which no other data are available are not included here. For information on these levels, see the ¹⁵⁵Gd(n,γ) E=th Data Set.

Levels: Model discussions of possible interest include:

Levels: Calculation of level energies, configurations, B(E2), or B(E3)(W.u.): 1967Su01, 1975Bi13, 1980De34, 1984SoZU, 1985So02, 1986No12, 1988Ba17, 1988De36, 1988Va20, 1990Ch18, 1990Ha22, 1990Se16, 1993So20, 1994So02, 1996So19, 1997So26.

Levels: Empirical formula for ground-state band level energies: 1988Ab07.

Levels: Calculation of deformation and Q: 1989BlZX

Levels: Separation of p and n deformation: 1986ElZW

Levels: E4 strength distribution: 1988Wu01

Levels: Fragmentation of E3 strength: 1990Co26

Levels: M1 strength distribution and decay of 1⁺ levels: 1987HeZQ, 1989De42, 1990Fa09, 1990Vl01, 1990Za08, 1990Za13, 1990Zi05, 1991Ra03

Gammas: The primary γ’s from the neutron-capture states (thermal, 1.9, and 58 keV) are not given here. The unplaced γ’s in ¹⁵⁵Gd(n,γ) and the ¹⁵⁶Eu β^- and ¹⁵⁶Tb ε decays are also not given. See those data sets for this information.

Gammas: In the calculation of the ρ²(E0) values for the E0 transitions, the "electronic " factors, |W, were taken from the tables of 1970Be87. For the transitions here, the K-to-Total ce ratios are all nearly the same and approximately equal to 1/1.14.