arXiv:2610.19555·v1·Nuclear Theory

R-process nuclei in the rare-earth region above N=126 in Relativistic Hartree-Bogoliubov theory: A preponderance of shape-coexistence in nuclei

M.M. Sharma

Abstract

The shell structure of nuclei beyond N=126 relevant to the third peak at A ~ 195 in r-process nuclear abundances in investigated. Within the framework of the relativistic Hartree-Bogoliubov theory in deformed space, a comparative study of the response of nuclei with three different model Lagrangians NL-SV1, SVI-2 and NL3 is made. Ground-state properties of even-even nuclei in the isotopic chains of Z=58-72 $= in t h e hi g h l y n e u t r o n - r i c h r e g i o na r e in v es t i g a t e d . A co m p a r i so n o f bin d in g e n er g i es w i t hma ss f or m u l a ss h o w s t ha t in t h ee x t r e m er e g i o n o f t h er - p r ocess p a t h, t h e R M F m o d e l S V I - 2 w i t h o u t n o n l in e a r i t i eso f s i g maan d o m e g am eso n ss h o w s an e x ce l l e n t a g r ee m e n tw i t h t h e ma ss f or m u l a H F B - 24. I t i ss h o w n t ha t ina l l t h e ab o v e L a g r an g ianm o d e l s, in t h e n e u t r o n r i c h r e g i o nb e tw ee n t h es h e l l c l os u r es N = 126 an d N = 184, t h er e i s a p r e p o n d er an ceo f n u c l i d ese x hibi t in g coe x i s t e n ceo f w e l l - d e f or m e d p r o l a t e an d o b l a t es ha p es in t h e g r o u n d s t a t e . A p r o l a t e g r o u n d s t a t e i ss h o w n t oe v o l v es m oo t h l y t o a coe x i s t in g o b l a t e g r o u n d s t a t e v iaan e a r d e g e n er a cy w i t h s u ccess i v e a dd i t i o n o f n e u t r o n s . I n d u ce d b y an o n se t o f d e f or ma t i o n f or$ N \ge 130$, nuclei approaching the r-process path are shown to exhibit enhanced stability in many isotopic chains (Z > 60). This has the effect of shifting the expected neutron drip line significantly farther into the neutron-rich region especially for the higher Z chains. Consequences of the enhanced stability, the shape co-existence and degeneracy of shapes in nuclei on the r-process nucleosynthesis are discussed.

Comments: Accepted in Physical Review C