Dr. Dennis Bonatsos

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Academic Career Length

25Years (2002-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

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3 August 2007 in Physical Review C

Journal Article

Staggering in γ-band energies and the transition between different structural symmetries in nuclei

The experimental energy staggering in γ bands of rare earths and actinides exhibits three distinct patterns as a function of angular momentum that are typical of well-deformed structural benchmarks: γ-soft for nuclei situated between a vibrator and a deformed γ-soft structure, axially symmetric for those between a vibrator and a rigid rotor, and triaxial γ-rigid for nuclei between a vibrator and a rigid triaxial rotor. The three patterns are reproduced by appropriate special solutions of the Bohr Hamiltonian, as well as by interacting boson approximation calculations. A particular quantity called S(4), which is proportional to the displacement of the

3_{γ}^{+}

level relative to the average of the

2_{γ}^{+}

and

4_{γ}^{+}

levels, can vary in magnitude and sign for different shapes and is found to give a good indication of structure and the evolution of structure. A sudden change in the γ-band staggering occurring between the vibrator and the axially symmetric rotor limits seems to be connected to the known presence of a first-order phase/shape transition in this region.

14 December 2007 in Physical Review C

Journal Article

Exactly separable version of the Bohr Hamiltonian with the Davidson potential

An exactly separable version of the Bohr Hamiltonian is developed using a potential of the form

u (β) + u (γ) / β^{2}

, with the Davidson potential

u (β) = β^{2} + β_{0}^{4} / β^{2}

(where

β_{0}

is the position of the minimum) and a stiff harmonic oscillator for

u (γ)

centered at

γ = 0^{°}

. In the resulting solution, called the exactly separable Davidson (ES-D) solution, the ground-state,

γ,

and

0_{2}^{+}

bands are all treated on an equal footing. The bandheads, energy spacings within bands, and a number of interband and intraband

B (E 2)

transition rates are well reproduced for almost all well-deformed rare-earth and actinide nuclei using two parameters (

β_{0}, γ

stiffness). Insights are also obtained regarding the recently found correlation between γ stiffness and the γ-bandhead energy, as well as the long-standing problem of producing a level scheme with interacting boson approximation SU(3) degeneracies from the Bohr Hamiltonian.

13 April 2006 in Physical Review C

Journal Article

E(5), X(5), and prolate to oblate shape phase transitions in relativistic Hartree-Bogoliubov theory

R. Fossion

Dennis Bonatsos

G. A. Lalazissis

Relativistic mean field theory with the NL3 force is used to produce potential energy surfaces (PESs) for a series of isotopes suggested as exhibiting critical point symmetries. Relatively flat PESs are obtained for nuclei showing the E(5) symmetry, whereas in nuclei corresponding to the X(5) case, PESs with a bump are obtained. The PESs corresponding to the Pt chain of isotopes suggest a transition from prolate to oblate shapes at

{}^{186}{Pt}

22 June 2005 in Physical Review C

Journal Article

Analytic description of critical-point actinides in a transition from octupole deformation to octupole vibrations

An analytic collective model in which the relative presence of the quadrupole and octupole deformations is determined by a parameter (

ϕ_{0}

), while axial symmetry is obeyed, is developed. The model [to be called the analytic quadrupole octupole axially symmetric model (AQOA)] involves an infinite well potential, provides predictions for energy and

B (EL)

ratios, which depend only on

ϕ_{0}

, draws the border between the regions of octupole deformation and octupole vibrations in an essentially parameter-independent way, and describes well

{}^{226}{Th}

and

{}^{226}{Ra}

, for which experimental energy data are shown to suggest that they lie close to this border. The similarity of the AQOA results with

ϕ_{0} = 45^{°}

for ground-state band spectra and

B (E 2)

transition rates to the predictions of the X(5) model is pointed out. Analytic solutions are also obtained for Davidson potentials of the form

β^{2} + β_{0}^{4} / β^{2}

, leading to the AQOA spectrum through a variational procedure.

27 April 2004 in Physical Review C

Journal Article

Sequence of potentials interpolating between the U(5) and E(5) symmetries

It is proved that the potentials of the form

β^{2 n}

(with

n

being integer) provide a “bridge” between the U(5) symmetry of the Bohr Hamiltonian with a harmonic oscillator potential (occurring for

n = 1

) and the E(5) model of Iachello (Bohr Hamiltonian with an infinite well potential, materialized for

n \to \infty

). Parameter-free (up to overall scale factors) predictions for spectra and

B (E 2)

transition rates are given for the potentials

β^{4}

β^{6}

, and

β^{8}

, corresponding to

R_{4} = E (4) ∕ E (2)

ratios of 2.093, 2.135, and 2.157, respectively, compared to the

R_{4}

ratios 2.000 of U(5) and 2.199 of E(5). Hints about nuclei showing this behavior, as well as about potentials bridging the E(5) symmetry with O(6) are briefly discussed. A note about the appearance of Bessel functions in the framework of

E (n)

symmetries is given as a by-product.

30 August 2023 in Atoms

Journal Article

Shape Coexistence in Even–Even Nuclei: A Theoretical Overview

The last decade has seen a rapid growth in our understanding of the microscopic origins of shape coexistence, assisted by the new data provided by the modern radioactive ion beam facilities built worldwide. Islands of the nuclear chart in which shape coexistence can occur have been identified, and the different microscopic particle–hole excitation mechanisms leading to neutron-induced or proton-induced shape coexistence have been clarified. The relation of shape coexistence to the islands of inversion, appearing in light nuclei, to the new spin-aligned phase appearing in

N = Z

nuclei, as well as to shape/phase transitions occurring in medium mass and heavy nuclei, has been understood. In the present review, these developments are considered within the shell-model and mean-field approaches, as well as by symmetry methods. In addition, based on systematics of data, as well as on symmetry considerations, quantitative rules are developed, predicting regions in which shape coexistence can appear, as a possible guide for further experimental efforts that can help in improving our understanding of the details of the nucleon–nucleon interaction, as well as of its modifications occurring far from stability.

About Me

Dennis Bonatsos received his B.Sc. degree in Physics from the University of Patras, Greece, in 1979, and his Ph.D. degree in Theoretical Nuclear Physics from the University of Pennsylvania, USA, in 1985. He is currently a Director of Research in the Institute of Nuclear and Particle Physics of the National Centre for Scientific Research (NCSR) Demokritos in Athens, Greece. He has held positions in the universities of Oxford (UK), Tuebigen (Germany), Fribourg (Switzerland), as well as in the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) in Trento (Italy). He has served on the Board of the Nuclear Physics Division of the European Physical Society (EPS), the committee of the Lise Meitner Prize in Nuclear Physics of the EPS, and the Board of Directors of NCSR Demokritos for many years. He has supervised 15 Ph.D. theses and has taught, for many years, postgraduate courses in the School of Applied Mathematical and Physical Sciences of the National Technical University of Athens. He has worked on algebraic models (including quantum groups) for nuclei, molecules, and atomic clusters, as well as on shape/phase transitions, and critical point symmetries (CPS) in atomic nuclei. In 2004-2006 he proposed the Z(5), Z(4), and X(3) CPS. In 2017 he proposed the proxy-SU(3) symmetry in atomic nuclei. He authored a book on algebraic models of nuclear structure (Clarendon, Oxford, 1988) and a postgraduate textbook on Advanced Quantum Mechanics (in Greek).

Dr. Dennis Bonatsos

Dr. Dennis Bonatsos

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