Toward understanding the microscopic origin of nuclear clustering

Abstract

Open Quantum System (OQS) description of a many-body system involves interaction of Shell Model (SM) states through the particle continuum. In realistic nuclear applications, this interaction may lead to collective phenomena in the ensemble of SM states. We claim that the nuclear clustering is an emergent, near-threshold phenomenon, which cannot be elucidated within the Closed Quantum System (CQS) framework. We approach this problem by investigating the near-threshold behavior of Exceptional Points (EPs) in the realistic Continuum Shell Model (CSM). The consequences for the alpha-clustering phenomenon are discussed.

Novel and simple description for a smooth transition fromα-cluster wave functions tojj-coupling shell model wave functions

“…These results for 0 + 1 and 0 + 2 agree with the modern understanding of cluster structure formation in 12 C [8,9]. A transition between the jj-coupling shell model structure and the three-α cluster structure occurs in the vicinity of the α-and triple-α-decay thresholds and can be seen in the near-threshold 0 + 2 state.…”

“…A generic explanation of this rule in terms of the collective external coupling of shell model states via the decay channel(s) has been put forward in Refs. [8,9]. In this context, α-cluster states are of particular interest because of strong binding of an α particle and a weak α-α interaction which does not allow to bind an α-α system.…”

Nucleon localization and fragment formation in nuclear fission

“…The binding-energy argument has often been used to explain properties of α-conjugate nuclei [6], cluster emission [7,8] and fission [9], and the appearance of a gas of light clusters in low-density nuclear matter [10][11][12] and in the interior region of heavy nuclei [13]. Another important factor is the coupling to decay channels; this explains [14,15] the very occurrence of cluster states at low excitation energies around cluster-decay thresholds [16].…”

Broad resonances in light nuclei studied withβ- andγ-spectroscopy

“…The nature and cause of nuclear clustering is discussed in [31,32]. Using density functional theory [31] concludes that clustering is a transitional phenomenon between crystalline and quantumliquid phases of fermionic systems, which is emphasized by the depth of the confining nuclear potential.…”

“…This has traces back to the 1960s and 1970s where Morinaga's original idea for the structure of the Hoyle state was that of a linear, crystal like, chain of three α-particles [3], while the microscopic cluster model of Uegaki [26] showed that a delocalised gas-like structure is more appropriate. [32] use the Shell-model extended to the continuum to argue that clustering is intimately related to the proximity of the continuum, and that the phenomenon therefore cannot properly be understood in closed quantum system calculations.…”