Evolution from spherical single-particle structure to stable triaxiality at high spins inNd140

Abstract

The level structure of 140 60 Nd 80 has been established up to spin 48 by in-beam γ -ray spectroscopy by use of the 96 Zr( 48 Ca, 4n) reaction. High-fold γ -ray coincidences were measured with the EUROBALL spectrometer. Twelve new rotational bands have been discovered at high spins. They are interpreted as being formed in a deep triaxial minimum at ε 2 ≈ 0.25 and γ ≈ 35 • . Possible configurations are assigned to the observed bands on the basis of configuration-dependent cranked Nilsson-Strutinsky calculations.

Multiple triaxial bands inNd138

“…In contrast to the Er-Lu-Hf nuclei, which are well deformed and most of the observed structures are rotational bands built on a triaxial shape, the Nd nuclei present a variety of shapes which coexist at high spins: multiple triaxial bands were observed in 138,139,140 Nd [15][16][17][18][19], spherical isomeric states were observed in 139,140 Nd [20,21], a highly deformed band was observed in 138 Nd [22], a superdeformed (SD) band was observed in 140 Nd [23]. The total number of bands identified in 138 Nd, including the 21 bands at low and medium spins reported recently in Ref.…”

“…This corresponds to a large alignment, i.e., several high-j particles which become strongly aligned at very low frequencies. As discussed previously [15][16][17][18], the high-j particles in these Nd isotopes are the h 11/2 protons and the neutrons which are excited to the orbitals built on the h 9/2 f 7/2 and i 13/2 subshells above the N = 82 gap. The large number of aligned particles are naturally combined with a triaxial shape [15][16][17][18], i.e., the bands are formed at triaxial shape with γ = 30 • −35 • and ε 2 = 0.2−0.3.…”

“…Another region of nuclei with stable triaxial shapes at high spins is the Nd region of nuclei with few holes in the N = 82 shell closure, in which many bands have been observed recently [15][16][17][18][19]. In contrast to the Er-Lu-Hf nuclei, which are well deformed and most of the observed structures are rotational bands built on a triaxial shape, the Nd nuclei present a variety of shapes which coexist at high spins: multiple triaxial bands were observed in 138,139,140 Nd [15][16][17][18][19], spherical isomeric states were observed in 139,140 Nd [20,21], a highly deformed band was observed in 138 Nd [22], a superdeformed (SD) band was observed in 140 Nd [23].…”

Switch from short-axis to intermediate-axis rotation in138Nd

“…At the highest spins the shape becomes axially symmetric with the rotation around the symmetry axis, as supported for example by lifetime measurements in the A = 110 region [4]. More recently, rotational high-spin bands in Nd nuclei with A = 138-140 have been identified [5][6][7][8], with an J (2) moment of inertia (defined from the differences in the E γ energies) which is less than half of the rigid body value. Such bands can only be formed at triaxial shape, where they are well understood from configurations with well-developed minima at ε 2 ≈ 0.25, γ ≈ 35 • , where the deformation of the nucleus is specified by ε 2 and γ ; see, e.g., Ref.…”

“…It has been shown previously that the minimum of the E − E rld curves is directly related to the maximum spin contribution from the high-j particles [6] or even more simply, from the number of high-j particles, i.e., to (p 1 + n 2 + n 3 ). With the minimum at I ≈ 27 for the T 1 and T 2 bands, we can then conclude that they should most likely be assigned to configurations with four high-j particles.…”