About Us
Atomic and Nuclear Physics

Contents


Introduction

The staff of the Department of Theoretical Physics carry out research in a wide variety of areas as outlined below. A significant part of our research is carried out as collaborative projects with colleagues at other Australian institutions and overseas.

Areas of Research

Parity Non-conservation and Time-invariance Violation in Atoms and Nuclei

This is one of the most interesting and challenging topic of the modern atomic and nuclear physics. It is focused on the investigation of the fundamental nature forces with the aim to contribute towards their grand unification. The information obtained by the measurements of parity non-conservation (PNC) and time invariance violation (TIV) in atoms is of the similar value as those which comes from huge and expensive accelerators. On the other side, the PNC and TIV effects in atoms are usually very small and require sophisticated experimental technique for the measurements and high-precision atomic calculations for the accurate interpretation of the experimental results.

Using the technique which is described below we have performed the most accurate calculations of the PNC effect in Cs, Fr, Tl, Pb and Bi. We are working on further improvement of the accuracy of calculations and on calculation of the PNC or TIV effects for those atoms where such measurements have been proposed (Dy, Hg, Ra, Ba+, etc.)(see, e.g. [1-3]).

References
[1] V. A. Dzuba, V. V. Flambaum, J. S. M. Ginges, Phys. Rev. D, 66, 076013 (2002).
[2] V. V. Flambaum, J. S. M. Ginges,Phys. Rev. A, 65, 032113 (2002).
[3] V. A. Dzuba, V. V. Flambaum, J. S. M. Ginges, M. G. Kozlov, Phys. Rev. A, 66, 012111 (2002).

Variation of Fundamental Constants

The possibility that fundamental constants (such as the speed of light, the electron charge and mass, the Planck constant, etc.) can change in time is predicted by some unified field theories. The detection of such a variation would be an important confirmation of these theories. The analysis of the spectra of distant quasars performed at UNSW does indicate that the fine structure constant alpha might be changing in time [1]. This analysis is done by a method suggested by our group [2]. It relies on the comparison of frequencies of electric dipole transitions of atoms in distant parts of the Universe (billions of light years away) with those on Earth. These frequencies are much more sensitive to the value of the fine structure constant than the fine structure intervals used in previous studies. Accurate relativistic calculations are used to link atomic frequencies with the fine structure constant (see, e.g. [3]).

References:
[1] J. K. Webb, V. V. Flambaum, C. W. Churchill, M. J. Drinkwater, and J. D. Barrow, Phys. Rev. Lett. 82, 884 (1999); J. K. Webb, M. T. Murphy, V. V. Flambaum, V. A. Dzuba, J. D. Barrow, C. W. Churchill, J. X. Prochaska, and A. M. Wolfe, Phys. Rev. Lett. 87, 091301 (2001).
[2] V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. Lett. 82, 888 (1999).
[3] V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. A 59, 230 (1999).

Isotope Shift

The isotope shift (IS) is a difference in energies of different isotopes of the same atom due to differences in nuclear mass and volume. Studies of isotope shifts are interesting for at least two reasons. First, the IS is an important systematic effect which could mimic the effect of a varying fine structure constant in absorption spectra of distant quasars. Second, a comparison of calculated and measured ISs is a way to study nuclear structure.

We are developing an all-order (in the Coulomb interaction) technique which would allow us to calculate ISs to very high precision.

Many-body theory and methods for high-precision atomic calculations

Many-body theory and methods for high-precision atomic calculations Relativistic Hartree-Fock (sometimes called Dirac-Hartree-Fock) method and Random-Phase Approximation (or Time-Dependent Hartree-Fock method in external field) are used as a starting point for high-precision calculations for many-electron atoms. To include electron correlations the following methods have been developed in our group:

  • Perturbation Theory in Screened Coulomb Interaction and Correlation Potential methods - for atoms with one valence electron (positron) above closed shells [1].
  • Combined Configuration Interaction and Many-Body Perturbation Theory method - for atoms with any number of valence electrons [2].
This enables us to perform calculations for many-electron neutral or nearly neutral atoms with the best accuracy available at present time. The Breit interaction (the magnetic interaction between atomic electrons) and radiative corrections can also be taken into account when nessasary [3].
References:
[1] V. A. Dzuba, V. V. Flambaum, O. P. Sushkov, Phys. Lett. A, 140, 493 (1989); Phys. Lett. A, 141, 147 (1989); V. A. Dzuba, V. V. Flambaum, A. Ya. Kraftmakher, O. P. Sushkov, Phys. Lett. A, 142, 373 (1989).
[2] V.A.Dzuba, V.V.Flambaum, M.G.Kozlov, Phys. Rev. A, 54, 3948 (1996).
[3] V. A. Dzuba, C. Harabati, W. R. Johnson, M. S. Safronova, Phys. Rev. A., 63, 044103 (2001).

PhD and Honours Projects

Calculation of Isotope Shift In Many-electron Atoms and Study of Fundamental Interactions

Supervisors: Prof. V. V. Flambaum, Dr. V. A. Dzuba

Isotope shift is the difference in optical spectra of different isotopes of the same atom. This difference is due to difference in mass and nuclear structure. Examining the effect of isotope shift on the atomic spectra of distant objects in the universe provides an opportunity to study isotope abundance evolution in early universe and test theories of nuclear reactions in stars and supernova. On the other hand, study of isotope shift in heavy atoms can be used to obtain valuable information about nuclear structure. This information is to be used to reduce uncertainty of experimental study of fundamental interactions in heavy many-electron atoms. In both cases accurate atomic calculations are needed for interpretation of experimental results.

The project involves using existing and developing new computer codes in Fortran, running these codes and combining theoretical and experimental results to extract information about fundamental interactions.

Study of Relativistic and Quantum Electrodynamics Effects In Many-electron Atoms

Supervisors: Prof. V. V. Flambaum, Dr. V. A. Dzuba

Electrons in heavy atoms move with speeds close to the speed of light. Therefore they should be treated relativistically for accurate results. Dominant relativistic corrections are usually included by replacing Schrödinger equations for single-electron states by Dirac equations. Breit and quantum-electrodynamic (QED) corrections are smaller relativistic effects which are not included in Dirac equation but still play important role in heavy atoms. Breit interaction is the difference between exact relativistic expression for the inter-electron interaction and its non-relativistic Coulomb approximation (e^2/r). Leading terms in this difference are magnetic interaction and retardation. QED corrections are due to interaction of atomic electrons with vacuum fluctuations.

Project involves developing and running Fortran computer codes for accurate relativistic calculations for heavy atoms. The results would contribute to the relativistic theory of atoms and help in interpretation of experimental investigation of fundamental interactions in heavy atoms.

Effects of Variation of Fundamental Constants of Nature From Big Bang to Atomic Clocks

Supervisors: Prof. V. V. Flambaum, Dr. V. A. Dzuba

Variation of fundamental constants (speed of light, electron electric charge, etc.) in space and time is suggested by theories unifying gravity with other interactions. Another argument for the variation comes from the anthropic principle. There must be very fine tuning of the fundamental constants which allows humans (and any life) to appear. This fine tuning can be naturally explained by the spatial variation of the fundamental constants. We appeared in the area of the Universe where the values of the fundamental constants are consistent with our existence.

The aim of this project is to search for the manifestation of the variation and perform necessary calculations of observable effects. For example, a change of the fundamental constants influences outcome of the Big Bang nucleosynthesis. The primordial amounts of deuterium, helium and lithium have been measured by astronomers. Comparing the calculations and measurements one can determine values of the fundamental constants after Big Bang. Variation of the fundamental constants also influences quasar spectra and ticking of different atomic clocks. A number of such measurements are now in progress. To interpret these measurements we should perform calculations of the variation effects for atomic transition frequencies. These calculations can be done using computer codes developed in our group. It is also very important to find new, enhanced effects of the variation and suggest new measurements.

This project may involve both analytical and numerical calculations in different areas of physics and cosmology, and may accommodate several PhD students.

Violation of Fundamental Symmetries In Atoms and Test of Grand Unification Theories

Supervisors: Prof. V. V. Flambaum, Dr. V. A. Dzuba

Recently great progress has been made in experiments on violation of parity and time reversal invariance in atoms. The aim of this project is to perform necessary atomic and nuclear calculations of the observed effects which are needed to test theories unifying all interactions of Nature. Different theories predict different strengths of weak interactions which violate parity and time reversal invariance, and comparison between the calculations and measurements will help to select correct theory.

It is also very important to find new, enhanced effects of the violation of the fundamental symmetries and suggest new measurements.

This project may involve both analytical and numerical calculations in atomic, nuclear and particle physics, and may accommodate several PhD students. Atomic calculations can be done using computer codes developed in our group.

Search for Strange Nuclear Matter in Earth's Atmosphere and Isotope Shift of Argon (honour project)

Supervisors: Prof. V. V. Flambaum, Dr. V. A. Dzuba

There are many theoretical arguments suggesting that nuclear matter with unusual properties might exist. Strange atoms contain nuclei with strange quarks. These atomic nuclei are expected to be much heavier than nuclei in normal atoms. The spectra of these exotic atoms has also to be slightly different from the spectra of normal atoms. This difference is due to different nuclear mass and nuclear volume and called isotope shift. If the value of isotope shift of a spectral line is known it can be used in experimental search for the strange nuclear matter. In general, isotope shift can be calculated. A set of methods and computer codes has been developed in our group for accurate calculations of isotope shift for many-electron atoms. Argon is the most abundant atomistic gas in Earth's atmosphere (other gases like nitrogen, oxygen, water vapour, etc. consist of molecules). Calculation of isotope shift for argon may help in search for strange nuclear matter in Earth's atmosphere. This calculation may also be used to search for black hole atoms (small charged black holes surrounded by orbiting electrons).

The project involves calculation of isotopic shifts using computer codes for atomic calculations developed by our group, collecting and interpreting the data and making suggestion for the search based on the findings.

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