New Visualization Technique of High-Spin Level Schemes: Double Helix Level Scheme of ¹⁷¹YbN. NicaCyclotron InstituteTexas A&M UniversityCollege Station, Texas, United States of America

Level and decay schemes are conventional tools for transmitting information on nuclear structure data, reason for which they are of interest not only for nuclear data evaluation community but for nuclear physics research community as well. The actual levels schemes are ad-hoc 2D graphs with an energy scale on the vertical direction and an arbitrary scale on the horizontal direction, where the bands can be interspersed freely. The ensemble of experimental bands gamma-ray energies as function of spin I can be described on average as a beam of parallel lines, 2c(2I+k-1), with constant 2c average beam slope, where c is the invers of the effective moment of inertia MoI_eff, c=ħ²/2MoI_eff; and k the integer-number band offset. The MoI_eff and k numbers can be determined by a least-squares fit applied simultaneously to all the bands of a nucleus. The experimental gamma-ray energies can be finally decomposed as 2c_band(2I+k+k’-1), with 2c_band inertial parameter and k’ an extra integer number, both generally changing with transition. This decomposition allows a unitary 3D representation of the rotational bands as paths on a special geometrical structure: a 3D double helix. For illustration we used the rotational bands of the ¹⁷¹Yb nucleus. The apparent rotations (precessions) of the bands on the double helix structure contain information on macroscopic and microscopic nuclear motion. At high excitation energies and spins the apparent rotation of the bands is generally clockwise, and changes to counterclockwise at low excitation energies and spins by backbending. The double helix level scheme is a fully correlated 3D structure that suggests a possible semiclassical vortex-like behavior for the nuclear rotational motion.