Home : Hasi Ray welcomes you to share her interests :

Link            "Ignorance is the origin of sufferings, so let us learn more."
  Niels Bohr (1885-1962)   "No Competition but Co-operation & No Community but Humanity

            "Let us make ourselves free from the sense of Possessions and Expectations which poison life."                    
                              LIST OF PHYSICS JOURNALS IMPACT FACTORS 2013 (please click)

                                   BASIC PHYSICS OF ATOMS AND THE APPLICATIONS :

     Bohr's model

     The understanding of basic facts about the nature is the foremost goal of the science. We try to use ideas, concepts and laws of physics to answer these questions. Much of what we know about the forces and interactions in atoms and nuclei has been learned from scattering experiments and theories, e.g. Rutherford's alpha ($\alpha $) ray scattering, the experiment and the theory.
  'Our exact calculation on Positronium and Hydrogen atoms scattering using an ab-initio close-coupling approximation theory predicts a new kind of binding. It appears that the forces due to dynamic dipole polarizability which is attractive, bind the system through exchange between the triplet electrons.'

   A. Low Energy Physics of Positron  & Positronium (Ps):

  • Positronium (Ps) & Atom Scattering:
      One of the most important discoveries in science is the existence of positron( e+), the antiparticle of electron( e- ) by Anderson in 1932. Again the theoretical prediction of the existence of Positronium(Ps) , the bound state of a positron and an electron by Mohorovicic(1934) and Ruark(1945) led to the experimental discovery of Ps in 1953 by Deutsch. The interesting property of this particle is that it is an isotope of hydrogen, whose charge and mass centers coincide. It is itself its antiparticle.

      Recent astrophysical observations of high energy spectra from various sources: from solar flares, from both the interstellar medium and a variable compact source in the general direction of the galactic center, from gamma-ray bursts have proved existence of 0.511 MeV photons. The characteristic three photon continuum resulting from ortho-positronium has also been observed from the direction of galactic center. At the same time the existence of elecrons and positrons in the astro-ambient medium has increased the importance of theoretical studies on Positron-atom and Ps-atom scattering.

      (a) IONISATION :

  • The Coulomb Born & Oppenheimer Approximation Theory :

       Ionisation is a very important reaction process in Ps and atom scattering. Different ionisation channels open just above corresponding thresholds. It is 6.8 eV for Ps, 13.6 eV for H, ~24.6 eV for He and ~5.4 eV for Li. We are studying three different types of ionisation: the Ps-ionisation, the target-ionisation and the ionisation of both the projectile and target atoms named both-ionisation. The most reliable Coulomb-Born approximation(CBA) theory is developed for the following Ps-atomic systems: (i)Ps-H system; (ii)Ps-He system; (iii)Ps-Li system.
A Coulomb-Born-Oppenheimer(CBO) theory is introduced in Ps-H scattering for Ps-ionisation to include the effect of exchange exactly.

       At very low energies below threshold the elastic scattering is important. The effect of exchange is negligible at intermediate and high energies. At the incident energies well above threshold there is almost no effect of exchange. For obtaining a complete picture about the dynamics of positronic systems, it is necessary to do studies on ionisation with targets of different nature. In this context, H is an ideal system where exact wavefunctions are known. He is the simplest closed shell atomic system and Li is the simplest among the alkali atoms. Alkali atoms have a very high polarizability (almost 30 times more than hydrogen), whereas in He it is not so important.

      The problem is challenging due to the fact that it is very difficult to perform calculation involving Ps and complex atomic system makes the problem more complicated.    


  • Using the Coupled-Channel Method and the Angular-momentum Algebra : 

       Ps-H system is a system of great fundamental importance since beginning of this field. There is no experimental data for this system. But there is no question about the theoretical acurateness of the problem since both, Ps and H are ideal systems and the atomic wavefunctions are perfectly known. In practice it is very difficult to carry on theoretical investigation through scattering since an infinite number of open channels need to be considered. But to search new physics, the scattering phenomenon is most desirable. It is of interests to study scattering phenomenon at the energy region below threshold where all the other channels are closed except the elastic one. On the otherhand, at very low energy region the system is highly complicated due to the fact that other effects like exchange of electrons, mutual polarization e.g. Van der Waals interaction, etc. have significant contributions.

       The close coupling approximation(CCA) methodology prescribed by Massey in 1932 is one of the most successful tool to study low energy scattering phenomenon. We have adapted this methodology in the Ps-H system where the wavefunctions of the initial and final channels are coupled through good quantum numbers in the eigen state expansion methodology. Ps is highly polarizable atom; its polarizability is eight times higher than normal hydrogen atom.

      Our motivation is to include effects of the forces due to polarizability together with exchange in the CCA scheme and to study different scattering parameters to search the basic physics.

   ***  B.   TWO-ATOMIC SCATTERING at cold energies : ***

     Very recently, I have introduced a new-model named modified static-exchange model (MSEM) using an ab-intio method considering all the Coulomb interaction terms exactly including the electron-electron exchange and the van der Waals interaction to evaluate the s-wave elastic phase shifts and the integrated elastic cross sections at cold energies for Ps and H system.  Again I have just introduced a new general code using static-exchange model (SEM) for two-atomic scattering when both the atoms are heavy. I have reproduced exactly the same data of Ps-H system just by  adjusting the parameters of the wavefunction and and the reduced mass of the system in the new code. In Ps-H system since Ps is a very light having a negligible mass in comparison to H, one can approximate the system as a three-centre problem. But in H-H system it should be strictly a four-centre problem.  So it was extremely difficult  to do the theoretical studies of  the system as accurately as necessity.  My new-code begins a new era in two-atomic collision physics.  At the beginning I planned to present the SEM data using the new code for Ps-H, H-H and Ps-Ps system. They will appear soon in arXiv and in journals.  Next  the present theory will be extended for Ps-Li and Li-Li, Ps-Na and Na-Na, Ps-K and K-K, Ps-Rb and Rb-Rb, Ps-Cs and Cs-Cs systems.  Later I like to include the van der Waals interaction in the new code.  I expect that it should provide a revolutionary new basic information in cold-atomic physics and also enrich the field of quantum computation.

     C. Theoretical Studies on Atomic Transitions :

  •  Physics of Highly Charged Ions using The Coupled-Cluster Approximation :

      The studies on atomic transitions is a subject of considerable interests in many fields. Extremely hot environment of the stars (for instances, corona of the sun, planetary nebulae etc.) show abundances of highly stripped ions. With the advent of many high resolution spectrographs, observation of weak or forbidden transition lines becomes possible and they are of great astrophysical interests. Many astrophysical phenomena like coronal heating, evolution of many chemical composition in the stellar envelope, determination of the chemistry in the planetary nebulae precursor's envelope are believed to be explained largely by these forbidden lines.

       The study of transition probabilities also plays an important role in astrophysics in the determination of atomic abundances. In controlled thermonuclear reactions, atomic radiation is one of the primary loss mechanism. In laboratory tokamak plasmas and in various astronomical objects, suitably chosen electric quadrupole (E2) forbidden lines serve as a basis for reliable electron density and/or temperature diagonostics. Accurate estimates of radiative transition probabilities among multiplet states are an important source for successful experimental identification of the spectra of astrophysical and laboratory plasma. Probabilities of magnetic dipole and electric quadrupole transitions, in particular, are important in plasma diagonostics, but experimental determination of these quantities is difficult, and accurate theoretical calculation only can provide important informations. More accurate studies are performed to find the term values and electric-quadrupole transitions for the highly stripped Na-like iso-electronic sequence of the iron group ions: (i) FeXVI, (ii) CoXVII and (iii) NiXVIII.

D.  Theoretical studies on parity non-conservation in heavy atomic systems caused by the nuclear anapole moments:

      For doing such studies to find basic physics, heavy atomic systems are more suitable. On the other hand, in heavy systems the accuracy of the atomic wavefunction is a great problem due to the strong Coulomb correlation and the relativistic effects. However, Dirac-Hartee-Fock wave functions can be used to include the relativistic effect, but proper inclusion of Coulomb correlation effect is a question. Many-body coupled-cluster method(CCM) is one of such tool which is very successful in alkali-like structure. I look for more accurate results by improving the basis with both bound and continuum orbitals and using CCM methodology for Cs.

                 !!! Search for electron's electric dipole moment. !!! 

E.   Bose-Einstein Condensation (BEC):

   (i) Laser Cooling, Trapping, Evaporative Cooling etc.
  (ii) Possible applications of BEC e.g. quantum computation & spintronics 
 (iii) Studies on basic physical properties of BEC
 (iv) The behaviour of cold atoms