Extracting the hexadecapole deformation from backward quasi-elastic scattering

Abstract

Background:The hexadecapole deformation β 4 is usually difficult to determine experimentally, especially its sign. The rapidly accumulated knowledge of β 2 inspires the desire of β 4 for radioactive nuclei, but the current low-quality beam is a severe experimental challenge. Therefore, a simple but sensitive method to extract β 4 in such a condition is urgently called for. Purpose: To study the feasibility of extracting β 4 from the lower-energy backward quasi-elastic (QEL) scattering. Methods:The QEL scattering at sub-barrier energy region is sensitive to the coupled-channels (CC) effect and consequently may be used to extract β 4 . The QEL scattering excitation functions for 16 O + 152 Sm, 170 Er, and 174 Yb were measured at a backward angle with small energy intervals at energies near the Coulomb barrier. Experimental fusion barrier distributions were also derived. The lower-energy data were analyzed to extract β 4 with the help of the CC calculations. Results: The obtained β 4 agrees with the available results reasonably well. Conclusions:We have demonstrated that the QEL scattering at sub-barrier energies provides a feasible and sensitive method to extract the value of β 4 , which is essentially meaningful for the radioactive nucleus because of its low beam intensity.

Mechanism of multinucleon transfer reaction based on the GRAZING model and DNS model

“…Transfer reactions also play an important role in the clarification of reaction mechanism transition from the quasielastic regime to a deeper area including deep inelastic and fusion [2,3]. For example, subbarrier neutron transfer will enhance the fusion probability of light nuclei [4][5][6], and transfer at higher energy provides a way to study the energy dissipation from the relative motion to the intrinsic excitation [7]. For the last two decades, many concerns have been raised about MNT reactions, which were predicted to produce neutron-rich isotopes of heavy nuclei following the works of [8][9][10][11][12][13].…”

Revisiting the island of hexadecapole-deformation nuclei in the A ≈ 150 mass region: focusing on the model application to nuclear shapes and masses

“…In the lanthanide and actinide regions, the existence and importance of the hexadecapole deformation was also revealed [29,30]. Furthermore, it is found that the β 4 deformation changes from large positive values around +0.1 to large negative values around −0.1 with increasing mass number A from 152 to 180 in the lanthanide region [30]. Nowadays, the β 4 measurements are still attracting considerable interest in nuclearphysics research.…”

“…More than 50 years ago, the hexadecapole deformation β 4 was accurately measured by α-scattering at energies well above the Coulomb barrier for rare-earth nuclei, showing that the β 4 deformations systematically evolute from positive in the light rare-earth nuclei to negative in the heavy nuclei [28]. In the lanthanide and actinide regions, the existence and importance of the hexadecapole deformation was also revealed [29,30]. Furthermore, it is found that the β 4 deformation changes from large positive values around +0.1 to large negative values around −0.1 with increasing mass number A from 152 to 180 in the lanthanide region [30].…”

Probes of axial and nonaxial hexadecapole deformation effects in nuclei around 230U

“…Relative to the quadrupole deformation β 2 , the hexadecapole deformation is difficult to determine experimentally with good precision, primarily because of its small magnitude [1,24]. Furthermore, all the results are model dependent and quite different with big uncertainties [25]. However, with the development of techniques and tactical skills, the bottleneck is being or will be broken.…”

“…The evidence for hexadecapole collectivity in closedshell nuclei was presented by examining the observed characteristics of the lowest 4 + excited state [27]. In the lanthanide nuclei, it is found that the β 4 deformation drops from large positive values around +0.1 to large negative values around −0.1 as the mass number A increases from 152 to 180 [25]. The β 4 measurements are indeed attracting much interest in research on nuclear shape.…”