Evolution Of Nuclear Structure Research Articles

The radioactive beam experiment at ISOLDE, REX‐ISOLDE

Radioactiveion beam (RIB) facilities make rich opportunities available for nuclear structure research well as for nuclear astrophysics and applied physics. RIB facilities dnve the increasing understanding of evolution of nuclear structure and the growing wealth of nuclear structure data. The Radioactive Beam Experiment at ISOLDE, REX ISOLDE, has been the dominant experiment in the past ISOLDE running period [13. REX‐ISOLDE profits from vast experience of ISOLDE production of radioactive beams more than 600 isotopes from elements. In addition the resonant ionisation laser ion source (RILIS) can provide beams with high selectivity, even isomeric beams. Since the end 2001 the LINAC has provided radioactive beams from the ISOLDE online separators with energies of 2. MeVIu towards two target stations One target station is used for efficient y-ray MINIBALL array and one target station is dedicated smaller experimental set-ups. In order make the full variety of beams from ISOLDE available for nuclear physics experiments the method of charge breeding of the singly charged radioactive ions has been employed [3] Hence the concept of REX-ISOLDE based on a large Penning trap which accumulates the radioactive ions from the ISOLDE mass separators and allows phase space cooling of the RIBS prepared, the ions are injected into Electron Beam Ion Source (EBIS), which raises the charge state of radioactive ion to an A/q < 4.5. The extracted highly charged ions are charge state selected with subsequent acceleration in a short LINAC. The LINAC allows the variationofthe beam energy between 0.8 and 2.2 MeVh in order to adjust the beam energy for experimental needs.

Structural Evolution Along Iso-Chains of Nuclei

The advent of radioactive nuclear beams (RNBs) has led to a rapid growth in the study of exotic nuclei. Already a number of major discoveries have been made. Examples are halo nuclei, mapping the bounds of nuclear existence, assessing the fragility of magicity, producing special nuclei such as 100Sn and 48Ni, and measuring key reaction rates of astrophysic interest. The growth in this field in the next decade will be enormous. With advanced RNB facilities being planned or under construction, more and more exotic nuclei will become accessible. One of the most interesting opportunities will be the study of the evolution of nuclear structure along extended iso-chains of nuclei. A prime example is Ni, where four magic numbers (20, 28, 40, and 50) and five major shells will be accessible. Structural evolution will be discussed from several standpoints, both theoretical and experimental, with emphasis on methods to obtain a maximum of information on new nuclei from the sparse data that will be available at the extremes of accessible N/Z ratios.

Evolution of nuclear structure in O(6)-like nuclei

The evolution of nuclear structure along the Xe and Ba isotopes with N{lt}82 is studied in comparison with that in the Pt-Os isotopes and with interacting boson approximation calculations. As is well known, the Pt isotopes from {sup 188{minus}196}Pt exhibit a stable structure very close to O(6), the lighter Pt isotopes and the Os nuclei evolve towards a rotor, and the heaviest Pt nuclei, {sup 198,200}Pt, show a tendency towards vibrational character. In contrast, we show that the Ba nuclei are best described by a trajectory from U(5) towards SU(3) that passes through an intermediate structure that resembles O(6) for N{approximately}72{endash}76. The Xe appears to evolve from U(5) to O(6)-like. {copyright} {ital 1998} {ital The American Physical Society}

Evolution of precollective nuclei and a tripartite classification of nuclear structure.

Precollective nuclei, that is, those with E(${4}_{1}^{+}$)/E(${2}_{1}^{+}$)2.0, are shown to evolve structurally in a very simple and universal way, in which E(${4}_{1}^{+}$) is linear against E(${2}_{1}^{+}$) with a slope of unity. A clue to this behavior is provided in terms of a seniority v=0 pair addition mode. Combined with recent studies of vibrator and rotor nuclei, this ``seniority'' regime gives a new tripartite global characterization of the evolution of nuclear structure.

Implications for evolution of nuclear structures of animals, plants, fungi and protoctists

The evolutionary variations of nuclear structure of animals, plants, fungi and protoctists were studied with electron microscopy by using techniques preferentially staining ribonucleoprotein (RNP) particles and chromatin. A remarkable similarity in the general morphological features of the RNP particles and chromatin arrangement is found in animals, plants and fungi. Important variations of these features were found in protoctists. These observations suggest that major evolutionary changes in the nuclear structure predate the acquisition of plastids by the ancestors of green plants. Once evolved, the nuclear structural pattern is conserved in plants and animals. Among protoctists studied, Kinetoplastida, Cryptomonadida and Volvocida have RNP particles and chromatin arrangement resembling those of plants and animals. These similarities may indicate a common ancestor. Important differences in the nuclear structure among Euglenida, Amebida, Cryptomonadida, Volvocida and Kinetoplastida support the view that Sarcomastigophora is a polyphyletic taxon. For the same reason Kinetoplastida and Euglenida must not be grouped in a monophyletic taxon. We propose that the variations of RNP particles may be related to the initial evolution of post-transcriptional processing.

Evolution of nuclear structure with increasing spin and internal excitation energy in 152Dy

The total γ ray spectrum emitted by 152Dy has been measured in two different reactions and decomposed into its constituent parts. From the measured decay times, multiplicities, multipolarities and spectral shapes, the average decay path has been reconstructed. The yrast single-particle structures have been shown to give way to highly collective bands at internal excitations energies > 1.5 MeV. A model, which takes into account the competition between statistical and collective decay at high spin and temperature, has been used to fit all features of the data, yielding Q t=7.0 +2.5 −1.5 e b for the collective bands.

Evolution of nuclear structure with increasing spin and internal excitation energy in 152Dy

Evolution of nuclear structure with increasing spin and internal excitation energy in 152Dy

Internal conversion and the evolution of nuclear structure at very high spin:Er154−158

The atomic charge state distributions of $^{154\ensuremath{-}158}\mathrm{Er}$ ions produced in fusion reactions with $^{32}\mathrm{S}$ and $^{34}\mathrm{S}$ beams and $^{126\ensuremath{-}130}\mathrm{Te}$ targets are used to deduce the average internal conversion probabilities of continuum $\ensuremath{\gamma}$ transitions at high spin. A strong dependence is observed on both neutron number and spin. For each of the nuclei $^{155\ensuremath{-}158}\mathrm{Er}$ a critical spin is observed at which a sudden enhancement of internal conversion occurs. This result alone implies either a sudden enhancement of $M1$ radiation, a sudden decrease of the average $E2$ transition energy, or some mixture of the two. In either case a major change in the underlying structure of the rotating body is implied. Previous continuum $\ensuremath{\gamma}$-ray spectroscopy measurements support the interpretation involving enhanced $M1$ radiation at very high spin.