Weighing the evidence for clustering in nuclei

Abstract

Clustering in nuclei is a long-standing topic in nuclear physics. While it has attracted much experimental and theoretical attention over the years, it is a model which is still controversial in terms of whether such clustering can be clearly delineated and separated from the complexity of nuclear structure described within more conventional nuclear models. In this sense, there is still ambiguity in terms of the uniqueness and relevance of the clustering description. What is often not clearly articulated is what would provide the most compelling evidence for clustering in different contexts. As a means of illustrating these issues, two strands of this topic will be discussed: alpha clustering in light nuclei and clustering in the 12C+12C system. Recent work in these areas will be reviewed and scope for future work will be highlighted.

Sub-barrier fusion cross section measurements with STELLA

“…With the measurement of deep sub-barrier light heavy-ion fusion cross sections, both insights into nuclear cluster effects [1] as well as the S -factor at energies of astrophysical interest can be obtained. On the production route towards heavier elements during the carbon burning phase in massive stars, 12 C( 12 C, 24 Mg) was identified as a key reaction [2].…”

Clustering in Stable and Exotic Light Nuclei

“…The structure of this state has been thoroughly investigated with theoretically modelled with both ab initio [44,45,52,53,54,55,56,57] and cluster models [58,59,60]. Much experimental progress has been achieved recently as far as the spectroscopy of 12 C near and above the α-decay threshold is concerned [61,62,63,64,65,66]. More particularly, the 2 + 2 "Hoyle" rotational excitation in 12 C has been observed by several experimental groups [61,63].…”

Recent Experimental Results on Nuclear Cluster Physics

“…Furthermore, the structure of possible octupole-unstable 3:1 nuclear shapes (hyperdeformation (HD) with β 2 ≈ 1.0) has also been discussed for actinide nuclei in terms of clustering phenomena [8]. Typical examples for the link between quasimolecular bands and extremely deformed (SD/HD) shapes can be found in the literature for A = 20 − 60 α-conjugate N =Z nuclei [8,18,36,52,54,55,56,57,58,59,60,61,62,63,64,65,66,67]. Highly deformed shapes and SD rotational bands have been discovered in several light α-like nuclei, such as 36 Ar and 40 Ca by using γ-ray spectroscopy techniques [57,59].…”