https://doi.org/10.1140/epja/i2019-12665-x
Review
“Stiff” deformed nuclei, configuration dependent pairing and the 
and 
degrees of freedom
1
University of Western Cape, Department of Physics, P/B X17, ZA-7535, Bellville, South Africa
2
iThemba Laboratory for Accelerator Based Sciences, National Research Foundation, PO Box 722, ZA-7129, Somerset-West, South Africa
3
National Radioactive Waste Disposal Institute, NECSA, Pelendaba, South Africa
4
National Metrology Institute of South Africa, Lynnwood Ridge, P/B X34, 0040, Pretoria, South Africa
5
Department of Physics, University of Zululand, Private Bag X1001, 3886, KwaDlangezwa, South Africa
* e-mail: jfss@tlabs.ac.za
Received:
17
May
2018
Accepted:
28
November
2018
Published online:
12
February
2019
We review the current experimental data on collective structures within the pairing gap of even-even deformed nuclei, with emphasis on nuclei near mass number 
. The essential physics that determines the characteristics of the first excited 0+ (02
+) state in these nuclei has been in dispute for several decades. Interpretation of these states in terms of surface quadrupole vibrations has often been challenged. We examine the role that configuration dependent pairing can play in these levels particularly at the onset of deformation as major shells fill. In all deformed nuclei rotational bands are found experimentally, starting at a state with spin 2+ with excitation energies near the middle of the pairing gap. These rotational bands, with quantum number 
, are usually referred to as bands and have been identified with quadrupole surface vibrations in the plane perpendicular to the major axis of deformation. However bands can also arise due to the breaking of axial symmetry of the quadrupole shape. We discuss data that can help with these different interpretations.
© SIF, Springer-Verlag GmbH Germany, part of Springer Nature, 2019
