Search

There has been plenty of empirical evidence which shows that the single-particle picture holds to a good approximation in atomic nuclei. In this picture, protons and neutrons move independently inside a mean-field potential generated by an interaction among the nucleons. This leads to the concept of nuclear shells, similar to the electronic shells in atoms. In particular, the magic numbers due to closures of the nucleonic shells, corresponding to noble gases in elements, have been known to play an important role in nuclear physics. Here we propose a periodic table for atomic nuclei, in which the elements are arranged according to the known nucleonic shells. The nuclear periodic table clearly indicates that nuclei in the vicinity of the magic numbers can be understood in terms of a shell closure with one or two additional nucleons or nucleon holes, while nuclei far from the magic numbers are characterized by nuclear deformation.

The evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution. In this work, we investigate the Z=6 spin-orbit shell gap towards the neutron dripline. To do so, we employed NA(p,2p)CA−1 quasi-free scattering reactions to measure the proton component of the 2 state of C. The experimental findings support the notion of a moderate reduction of the proton 1p−1p spin-orbit splitting, at variance to recent claims for a prevalent Z=6 magic number towards the neutron dripline.

In addition to the formulas (1) and (2) from work of the author (Bezdenezhnyi, 1999, hereafter Paper I) alternative formulas (3)--(6) are derived for description of two sequences of magic numbers. Their properties are described. Dependences of some physical parameters as a function of the number of chemical element (Z), number of neutrons (N) and the mass number (A) are analyzed. It is shown that magic numbers of protons (Z) and neutrons (N) are displayed in them. The concept of magic mass numbers (A) is proposed, and it is shown that they are also present in some dependences. The list of magic and twice magic (on Z and N) elements is extended, as well as the list of twice magic ones on A and Z or N. We propose to refer a nucleus that contains magic numbers of protons and neutrons to thrice magic nucleus if their sum is a magic number too. It is suggested that during the decay of "double-uranium" super-nucleus one of three twice magic elements ( X(112,168), Y(126,184) and Z(168,258) or Z'(168,240) ) predicted (in Paper I) will be formed fragment accompanying in areas of twice magic nuclei: Yb(70,112), Sn(50,70) and S(16,16) respectively.

The binding energy, equilibrium geometry, and vibration frequencies of free clusters Cu n (2 ≤ n ≤ 20) are calculated using the potentials of interatomic interactions found using the tight-binding approximation. The nonmonotonic dependence of the clusters' minimum vibration frequency on their sizes and the extreme values for the number of atoms in a cluster n = 4, 6, 13, and 19 is demonstrated. It is noted that this result agrees with the theoretical and experimental data on stable structures of small and medium metallic clusters. © 2013 Pleiades Publishing, Ltd.

Water clusters are known to undergo an autoprotonation reaction upon ionization by photons or electron impact, resulting in the formation of (H2O)(n)H3O+. Ejection of OH cannot be quenched by near-threshold ionization; it is only partly quenched when clusters are complexed with inert gas atoms. Mass spectra recorded by electron ionization of water-doped helium droplets show that the helium matrix also fails to quench OH loss. The situation changes drastically when helium droplets are codoped with C-60. Charged C-60-water complexes are predominantly unprotonated; C-60(H2O)(4)(+) and (C-60)(2)(H2O)(4)(+) appear with enhanced abundance. Another intense ion series is due to C-60(H2O)(n)OH+; dehydrogenation is proposed to be initiated by charge transfer between the primary He+ ion and C-60. The resulting electronically excited C-60(+)* leads to the formation of a doubly charged C-60-water complex either via emission of an Auger electron from C-60(+)*, or internal Penning ionization of the attached water complex, followed by charge separation within {C-60(H2O)(n)}(2+). This mechanism would also explain previous observations of dehydrogenation reactions in doped helium droplets. Mass-analyzed ion kinetic energy scans reveal spontaneous (unimolecular) dissociation of C-60(H2O)(n)(+). In addition to the loss of single water molecules, a prominent reaction channel yields bare C-60(+) for sizes n=3, 4, or 6. Ab initio Hartree-Fock calculations for C-60-water complexes reveal negligible charge transfer within neutral complexes. Cationic complexes are well described as water clusters weakly bound to C-60(+). For n=3, 4, or 6, fissionlike desorption of the entire water complex from C-60(H2O)(n)(+) energetically competes with the evaporation of a single water molecule. (C) 2010 American Institute of Physics.

We have used photo-ionisation efficiency spectroscopy to determine the ionisation potentials (IPs) of the niobium-carbide clusters, Nb5Cy (y = 0-6). Of these clusters Nb5C2 and Nb5C3 exhibit the lowest IPs. Complementary density functional theory calculations have been performed to locate the lowest energy isomers for each cluster. By comparing the experimental IPs with those calculated for candidate isomers, the structures of the Nb5Cy clusters observed in the experiment are inferred. For all these structures, the underlying Nb-5 cluster has either a "prolate'' or "oblate'' trigonal bipyramid geometry. Both Nb5C5 and Nb5C6 are shown to contain carbon-carbon bonding in the form of one and two molecular C-2 units, respectively.

We report the observation of large (n up to -25) acetylene and methylacetylene cluster ions- the largest yet reported from ionization of neutral (C2H2)n or (CH3CCH)n clusters. The cluster ion intensity distributions of both systems display prominent magic numbers at n = 3. This finding is indicative of intraclusters ion-molecule reactions giving rise to what are most likely benzene and trimethylbenzene ions from (C2H2)n+ and (CH3CCH)n+ cluster ions, respectively. The acetylene cluster ion intensity distributions observed under efficient clustering conditions are further characterized by unexpected features, most notably a sharp break at n = 7 and a strong magic number at n 14. The mass spectra of methyl-acetylene display a less dramatic break at n 7 and a weak magic number around n 10. These surprising structures may arise as a result of the formation of particularly stable covalently bonded molecules ions. In view of the unique properties of carbon it is possible that these ions possess spherical cage geometries reminiscent of the fullerenes.

When neutral van der Waals clusters, produced in a supersonic expansion, are ionized the resulting cluster ion distribution can exhibit dramatic intensity anomalies for very specific cluster sizes. These 'magic numbers' typically result from a particularly stable cluster ion geometry generated by the completion of a full solvent shell around a central ion core. In this paper we will review our current work which employs magic numbers as a probe, not only of cluster ion structure, but also of chemical reactivity within these species. That is, the appearance of certain magic numbers can be attributed to unique cluster reactions occurring between the ion and the solvating molecules within the cluster., Prepared for publication in Royal Society of Chemistry Chemical Society Reviews.