Paradigmatic Lessons from Nuclear Driplines

Abstract

Science is—as emphasized 50 years ago by Thomas Kuhn in his academic bestseller The Structure of Scientific Revolutions—driven by paradigms, rooted in outstanding discoveries and practice. At the centennial for the nuclear atom, it may be appropriate to address the current paradigmatic situation for nuclear physics on background of the large investments made during the last decades. Following Rutherford’s paradigm, nuclear physics has developed by colliding nuclei and from studying the fragments that emerge. With restriction to new forms of transient cold nuclear matter, we will address if and how new discoveries have influenced the way we think about nuclear architecture, drawing parallels with comparable development in other branches of science. Recent discoveries in halo nuclei, $^{11}$Be and the Borromean $^{22}$C will serve as our cardinal examples. The challenges at driplines may appear less dramatic than what calls for a Kuhnian turnover, still we hope to convey that valuable lessons may be learned. The attention-grabbing dripline lessons we address are rooted in emergent degrees of freedom involving cluster constituents. This is a great challenge for the ruling paradigm, a shell-model inspired ab initio nucleon-based theory, developed and tested for stable nuclei, and currently being tuned to encompass dripline lessons. Our mental pictures and dynamic understanding of many of the outstanding dripline phenomena will, however, remain linked to cluster degrees of freedom. This duality makes our paradigmatic lessons conceptually less dramatic than what Kuhn’s “incommensurability” may imply.