A new kind of natural radioactivity

Rose, H. J.; Jones, G.

doi:10.1038/307245a0

Cited by 623 publications

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“…The binding energy of the α-particle, formed from two protons and two neutrons, is much larger than in other light nuclei. Cluster radioactivity [10], discovered in the 80's, is another manifestation of clustering in atomic nuclei. Experimental signatures of clustering are usually indirect.…”

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confidence: 99%

How atomic nuclei cluster

Ebran

Khan

Nikšić

et al. 2012

Nature

176

244

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Nucleonic matter displays a quantum liquid structure, but in some cases finite nuclei behave like molecules composed of clusters of protons and neutrons. Clustering is a recurrent feature in light nuclei, from beryllium to nickel. For instance, in 12 C the Hoyle state, crucial for stellar nucleosynthesis, can be described as a nuclear molecule consisting of three alpha-particles. The mechanism of cluster formation, however, has not yet been fully understood. We show that the origin of clustering can be traced back to the depth of the confining nuclear potential. By employing the theoretical framework of energy density functionals that encompasses both cluster and quantum liquid-drop aspects of nuclei, it is shown that the depth of the potential determines the energy spacings between single-nucleon orbitals, the localization of the corresponding wave functions and, therefore, the degree of nucleonic density clustering. Relativistic functionals, in particular, are characterized by deep single-nucleon potentials. When compared to non-relativistic functionals that yield similar ground-state properties (binding energy, deformation, radii), they predict the occurrence of much more pronounced cluster structures. More generally, clustering is considered as a transitional phenomenon between crystalline and quantum liquid phases of fermionic systems.The occurrence of molecular states in atomic nuclei and the formation of clusters of nucleons were already predicted in the 30's by von Weizsäcker and Wheeler [1,2]. Even though the description of nuclear dynamics became predominantly based on the concept of independent nucleons in a mean-field potential, a renewed interest in clustering phenomena in the 60's led to the development of dedicated theoretical methods [3]. Numerous experimental studies have revealed a wealth of data on clustering phenomena in light nuclei [4], and modern theoretical approaches use microscopic models that fully take into account single-nucleon degrees of freedom [5][6][7]. Clustering gives rise to nuclear molecules. For instance, in 12 C the second 0 + state the Hoyle state that plays a critical role in stellar nucleosynthesis, is predicted to display a three-α structure [8,9]. The binding energy of the α-particle, formed from two protons and two neutrons, is much larger than in other light nuclei. Cluster radioactivity [10], discovered in the 80's, is another manifestation of clustering in atomic nuclei. Experimental signatures of clustering are usually indirect. Quasi-molecular resonances are probed by scattering one cluster on another, such as in the 12 C+ 12 C system [4,11], and cluster structures are also discernible in the breakup of nuclei. Evidence has been reported for the formation of clusters in ground and excited states of a number of α-conjugate nuclei [4], that is nuclei with an equal even number of protons and neutrons, from 8 Be to 56 Ni.The mechanism of cluster formation in nuclei has not yet been fully understood. Deformation plays an important role because it removes the degenera...

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confidence: 99%

How atomic nuclei cluster

Ebran

Khan

Nikšić

et al. 2012

Nature

176

244

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“…The dynamical cluster-decay model developed here for hot compound nucleus is an adaptation of the preformed cluster model (PCM) of Gupta et al [24,25,26,27,28] for ground-state decays, which itself is based on the well-known quantum mechanical fragmentation theory, the QMFT [29,30,31], given for fission and heavy-ion reactions and used later for the prediction of exotic cluster radioactivity [9,32,33]. In the preformed cluster model, the decay half-life T1 2 , or the decay constant λ, is defined as…”

Section: The Dynamical Cluster Decay Modelmentioning

confidence: 99%

Emission of intermediate mass fragments from hot¹¹⁶Ba* formed in low-energy⁵⁸Ni +⁵⁸Ni reaction

Balasubramaniam

Kumar

Gupta

et al. 2003

J. Phys. G: Nucl. Part. Phys.

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The complex fragments (or intermediate mass fragments) observed in the low-energy 58 Ni+ 58 Ni→ 116 Ba * reaction, are studied within the dynamical cluster decay model for s-wave with the use of the temperature-dependent liquid drop, Coulomb and proximity energies. The important result is that, due to the temperature effects in liquid drop energy, the explicit preference for α-like fragments is washed out, though the 12 C (or the complementary 104 Sn) decay is still predicted to be one of the most probable α-nucleus decay for this reaction. The production rates for non-α like intermediate mass fragments (IMFs) are now higher and the light particle production is shown to accompany the IMFs at all incident energies, without involving any statistical evaporation process in the model. The comparisons between the experimental data and the (s-wave) calculations for IMFs production cross sections are rather satisfactory and the contributions from other ℓ-waves need to be added for a further improvement of these comparisons and for calculations of the total kinetic energies of fragments.

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“…For smaller systems, the phenomenon of alpha clustering is important both in low density nuclear matter [3], as well as in light nuclei [4]. In the case of heavy nuclei, cluster aggregation is manifested in the spontaneous phenomenon of clusters, from the common process of α decay to the emission of more exotic clusters such as 14 C [5]. The reduction of density near the nuclear surface, allows formation of α particles, or other clusters, and their emission from either ground-state or modestly excited nuclei.…”

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Tidal Effects and the Proximity Decay of Nuclei

et al. 2007

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We examine the decay of the 3.03 MeV state of 8 Be evaporated from an excited projectile-like fragment following a peripheral heavy-ion collision. The relative energy of the daughter α particles exhibits a dependence on the decay angle of the 8 Be * , indicative of a tidal effect. Comparison of the measured tidal effect with a purely Coulomb model suggests the influence of a measurable nuclear proximity interaction. Aggregation of clusters in a dilute medium is a process that impacts a wide range of physical phenomena from the formation of galactic structure[? ] to formation of Van der Waals clusters in a low density gas [? ]. This aggregation can involve the delicate interplay of elementary forces that results in a frustrated system. One such example is the formation of pasta nuclei in the crust of a neutron star [1,2]. For smaller systems, the phenomenon of alpha clustering is important both in low density nuclear matter [3], as well as in light nuclei [4]. In the case of heavy nuclei, cluster aggregation is manifested in the spontaneous phenomenon of clusters, from the common process of α decay to the emission of more exotic clusters such as 14 C [5]. The reduction of density near the nuclear surface, allows formation of α particles, or other clusters, and their emission from either ground-state or modestly excited nuclei. Cluster emission, thus primarily probes the surface properties of the emitting nucleus [6]. Our present understanding of cluster emission is largely based upon the yields, kinetic energy spectra, and angular distributions of emitted clusters -all of which are well described within a statistical transition-state formalism [7]. In this Letter we present for the first time evidence for the modification of cluster emission by interaction with the nuclear surface. We probe the interaction of the nuclear surface with the emitted cluster by using resonance spectroscopy to examine the emission of 8 Be * and specifically explore how its decay is impacted by the tidal effect [8].Charged-particles produced in the reaction 114 Cd+ 92 Mo at E/A=50 MeV were detected in an exclusive 4π setup. To focus on evaporated fragments, we selected peripheral collisions through detection of forward-moving projectile-like fragments (PLFs) with 10≤Z≤48, in the angular range 2.1 • ≤θ lab ≤4.2 • with ∆θ lab ≈0.13 • [9]. This PLF is the decay residue of the excited primary projectile-like fragment (PLF * ) formed by the collision. Light-charged-particles and fragments with Z≤9 were isotopically identified [9] in the angular range 7 • ≤θ lab ≤58

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A new kind of natural radioactivity

Cited by 623 publications

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How atomic nuclei cluster

How atomic nuclei cluster

Emission of intermediate mass fragments from hot¹¹⁶Ba* formed in low-energy⁵⁸Ni +⁵⁸Ni reaction

Tidal Effects and the Proximity Decay of Nuclei

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A new kind of natural radioactivity

Cited by 623 publications

References 0 publications

How atomic nuclei cluster

How atomic nuclei cluster

Emission of intermediate mass fragments from hot116Ba* formed in low-energy58Ni +58Ni reaction

Tidal Effects and the Proximity Decay of Nuclei

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Emission of intermediate mass fragments from hot¹¹⁶Ba* formed in low-energy⁵⁸Ni +⁵⁸Ni reaction