Recent advances in nuclear physics through on-line isotope separation

Abstract

Nuclear physics is advancing rapidly at the precision frontier, where measurements of nuclear observables are challenging state-of-the-art nuclear models. A major contribution is associated with the increasing availability of accelerated beams of radioactive ions produced using the isotope separation on-line technique. These advances have come hand in hand with significant progress in the development of high-e ciency detector systems and improved target technologies which are invaluable in exploiting these beams to their full advantage. This article reviews some of the recent highlights in the field of nuclear structure profiting from these technological advances.N uclear physics is a mature science with strong connections to both fundamental physics and nuclear astrophysics, namely the origin of the chemical elements 1,2 . Nuclear physics is over 100 years old, but there are still key outstanding questions. This reflects the challenge and complexity of describing the nucleus from a theoretical perspective. In principle, ab initio calculations of nuclear properties are desirable, but current computing power limits these types of calculations to around A = 12 (ref. 3). As many nuclides have of the order of 100 nucleons, simplifying assumptions are usually applied to describe their behaviour. Complementary descriptions of the nucleus exist in terms of the behaviour of individual nucleons-single-particle models 4 -or in terms of the coherent behaviour of the nucleons that make it up-collective models 5,6 . These models offer an excellent description of both stable isotopes and those near to stability. To challenge these models, however, and make extrapolations valid in extreme astrophysical scenarios (such as supernova explosions), it is necessary to probe exotic, short-lived, radioactive nuclei. Present experimental efforts in nuclear structure are pushing towards two frontiers: the limits of existence, in other words, what combinations of protons and neutrons can exist as bound systems 7,8 ? and the precision frontier, where nuclear models may be challenged in detail by obtaining precision data on nuclear observables. To obtain the precision needed to make discriminating tests of nuclear models, the playground for relevant measurements comprises radioactive nuclei-in particular, those closer to stability, where significant beam intensities are achievable. The increasing availability of accelerated radioactive beams produced using the isotope separation on-line (ISOL) technique is contributing strongly to a renaissance in the field of nuclear physics. The ISOL technique dates back to the 1960s (ref. 9), but the ability to re-accelerate such beams was pioneered in the 1990s at Louvain-la-Neuve 10 , and has only begun to flourish in the past five years or so. This article presents an overview of physics with accelerated ISOL beams, focusing on recent advances and experimental highlights in the field of nuclear structure.There are two main ways of creating radioactive beams: ISOL and fragmentation. The ISOL technique,...

Partial dynamical symmetries and shape coexistence in nuclei

“…The shape can be spherical (β = 0) or deformed (β > 0) with γ = 0 (prolate), γ = π/3 (oblate), 0 < γ < π/3 (axially asymmetric) or γ-independent. The equilibrium deformations associated with the DS limits conform with their geometric interpretation and are given by β eq = 0 for U (5), (β eq = √ 2, γ eq = 0) for SU (3), (β eq = are manifested in nuclear structure, where extensive tests provide empirical evidence for their relevance to a broad range of nuclei [38,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]. In addition to nuclear spectroscopy, Hamiltonians with PDS have been used in the study of quantum phase transitions [58,59,60] and of systems with mixed regular and chaotic dynamics [61,62].…”

Collectivity in the light radon nuclei measured directly via Coulomb excitation

“…Experiments involving very heavy (A > 200), post-accelerated beams have proven successful at REX-ISOLDE in recent years, including those employing radon [26]. Studies such as these, performed at ISOL facilities around the world, are currently pushing the boundaries of nuclear spectroscopy on the precision frontier in exotic nuclei [27].…”

Algebraic benchmark for prolate-oblate coexistence in nuclei

“…Such shape coexistence in the same nucleus is known to occur widely across the nuclear chart [1,2]. The increased availability of rare isotope beams and advancement in high-resolution spectroscopy, open new capabilities to investigate such phenomena in nuclei far from stability [3].…”

“…Inter-band (g 2 ↔ g 1 ) E2 transitions, are extremely weak. This follows from the fact that the L-states of the g 1 and g 2 bands exhaust, respectively, the (2N, 0) and (0, 2N ) irrep of SU(3) and SU (3). T(E2) as a (2, 2) tensor under both algebras can thus connect the (2N, 0) irrep of g 1 only with the (2N − 4, 2) component in g 2 which, however, is vanishingly small.…”