• V S Ramamurthy

      Articles written in Pramana – Journal of Physics

    • Statistical properties of excited fissioning nuclei

      S S Kapoor V S Ramamurthy

      More Details Abstract Fulltext PDF

      The phenomenon of the disappearance of the shell effects on the thermodynamic properties of nuclei with increasing excitation energy has been examined quantitatively on the basis of numerical calculations based on realistic shell model single particle level schemes. It is shown that shell effects disappear at moderate excitation energies and above these excitation energies, the thermodynamic behaviour of the nucleus is identical to that of the equivalent liquid drop model nucleus. Implications of the above feature in the interpretation of some aspects of fission of excited nuclei such as mass-asymmetry and angular anisotropy are examined. The relationship of the phenomenon of washing out of shell effects at high excitation energies with the temperature smearing method of determining ground state shell correction energies is also outlined.

    • Nuclear level densities in self-consistent field approximation

      S K Kataria V S Ramamurthy

      More Details Abstract Fulltext PDF

      The effect of two-body nature of the nuclear shell model potential on the recent numerical calculations of the nucleai level density has been examined. For the two most widely used single particle energy level schemes based on harmonic oscillator and Woods-Saxon potential, this effect is shown to significantly modify the excitation energy dependence of the level densisties.

    • Prompt gamma ray multiplicity distributions in spontaneous fission of252Cf

      V S Ramamurthy R K Choudhury J O Mohankrishna

      More Details Abstract Fulltext PDF

      The shape parameters of the multiplicity distribution of prompt gamma rays emitted in spontaneous fission of252Cf were obtained using the multiple coincidence technique. The multiplicity distribution is well represented by a Gaussian distribution. Assuming the average number of prompt gamma rays emitted per fission to be 10.3, the standard deviation of the multiplicity distribution was estimated to be 4.2±0.4. The variation of the standard deviation of the multiplicity distribution has also been obtained as a function of kinetic energy of one of the fragments and was found to exhibit a strong zigzag dependence on the single fragment kinetic energy. The results have been discussed on the basis of the emission mechanism of prompt gamma rays in fission.

    • Search for superheavy elements in monazite from beach sands of South India

      S S Kapoor V S Ramamurthy M Lal S K Kataria

      More Details Abstract Fulltext PDF

      Monazite minerals obtained from beach sands of South India were examined for the presence of superheavy elements with photon-induced x-ray fluorescence method. The accumulated data of a number of runs each of several days duration do not show any convincing peaks above the background at the expected locations for superheavy elements which are above the present sensitivity of detection of about 10 ppm by weight for element 126. However, some intriguing features pertaining to structures in the x-ray spectra around 27 keV were observed, which are of interest for further investigations.

    • Evaluation of nuclear shell correction energies for realistic level schemes by temperature smearing method

      V S Ramamurthy S S Kapoor

      More Details Abstract Fulltext PDF

      Calculations of shell correction energies by the temperature smearing method for realistic single particle level schemes of finite depth potentials are described and discussed. It is found that the method provides unique values of the shell correction energies for the various shapes relevant in the fission of actinide nuclei including those shapes where breakdown of the usual Gaussian energy smearing procedure was observed.

    • Multiplicity distribution of prompt gamma rays in spontaneous ternary fission of252Cf

      V S Ramamurthy R K Choudhury J C Mohana Krishna

      More Details Abstract Fulltext PDF

      The first and the second moments of the multiplicity distribution of prompt gamma rays in spontaneous ternary fission of252Cf have been measured by the multiple coincidence technique. While both these moments were found to be nearly independent of the energy of the light charged particle accompanying the fission fragments, the width of the multiplicity distribution was larger than that in the case of normal binary fission by about 20%.

    • Analysis of fission excitation functions and the determination of shell effects at the saddle point

      V S Ramamurthy S S Kapoor

      More Details Abstract Fulltext PDF

      A method is proposed to deduce the shell correction energy corresponding to the fission transition state shape of nuclei in the mass region around 200, from an analysis of the first chance fission values of the ratio of fission to neutron widths, (Γfn)1. The method is applied to the typical case of the fissioning nucleus212Po, formed by alpha bombardment of208Pb. For the calculation of the neutron width, the level densities of the daughter nucleus after neutron emission were obtained from a numerical calculation starting from shell model single particle energy level scheme. It is shown that with the use of standard Fermi gas expression for the level densities of the fission transition state nucleus in the calculation of the fission width, an apparent energy dependence of the fission barrier height is required to fit the experimental data. This energy dependence, which arises from the excitation energy dependence of shell effects on level densities, can be used to deduce the shell correction energy at the fission transition state point. It is found that in the case of212Po, the energy of the actual transition state point is higher than the energy of the liquid drop model (LDM) saddle point by (3 ± 1) MeV, implying significant positive shell correction energy at the fission transition state. Further, the liquid drop model value of level density parametera is found to be a few per cent smaller for the saddle point shape as compared to its spherical shape.

    • Classical microscopic description of particle cluster collisions: application to heavy ion collisions

      V S Ramamurthy S K Kataria

      More Details Abstract Fulltext PDF

      A classical microscopic description of the collision between two bound particle clusters, interacting via a suitable two body force is presented with a view to extend the analogy to nuclear collisions. It is shown that with a proper choice of the parameters of the two body force, the model calculations can bring out qualitatively all the essential features of low energy heavy ion collisions such as complete fusion, deep inelastic scattering and nucleon transfers. The model avoids some of the limitations of purely hydrodynamic descriptions connected with the shape parametrization, compressibility and viscosity effects, etc.

    • Classical description of low energy16O +16O collisions

      A N Dixit V S Ramamurthy Y R Waghmare

      More Details Abstract Fulltext PDF

      The aim of this paper is to study the scattering of the two ground state16O nuclei, using classical microscopic approach. We have studied fusion cross-section (σF) for various incident energies, its energy variation with time, and also other aspects such as shape deformation in head-on collision, life-time of resonance-scattering etc. Our calculations indicate that for projectile energies of the order of 1–2 MeV per nucleon (low energies) classical microscopic calculations for heavy ion reactions seem to give satisfactory description. However, at very low energies (less than 1 MeV/nucleon) appreciable deviations are seen which may indicate the breakdown of classical approximations.

    • Fusion-fission angular distributions: A new probe of fast fission fractionation in nucleus-nucleus collisions

      S S Kapoor V S Ramamurthy R Ramanna

      More Details Abstract Fulltext PDF

      Fragment angular distributions in heavy ion-induced fission reactions have been analysed in terms of a two component model—fission following compound nucleus formation and fast fission events. It is seen that, contrary to the general assumption, fast fission competes with compound nucleus fission even when the composite system is formed with a spin less than the rotating liquid drop model limit for vanishing fission barrier.

    • Nucleon transport processes in fission and heavy ion reactions

      S S Kapoor V S Ramamurthy

      More Details Abstract Fulltext PDF

      The nucleon exchange process between two nuclei in close proximity and its application to an explanation of fragment mass and charge distributions in fission and in heavy ion deep inelastic collisions are reviewed. An analysis of the measured correlations between the energy loss from relative motion and the fragment mass and charge variances in the heavy ion deep inelastic collisions is presented. The recent data on fragment mass and charge variances as a function of the fragment kinetic energy in thermal neutron induced fission of235U, lends added support to the hypothesis that the nucleon transport process plays a similar role both in fission and in heavy ion deep inelastic collisions.

    • Surface diffuseness of deformed and rotating nuclei

      Alok Saxena V S Ramamurthy

      More Details Abstract Fulltext PDF

      The surface diffuseness of deformed and rotating nuclei has been studied using the energy density formalism. It is shown that the surface diffuseness exhibits an anisotropy. This anisotropy in surface diffuseness can result in an anisotropic charged particle emission from highly spinning nuclei as has been seen in some recent experiments.

    • Nucleon exchange mechanism of mass asymmetry relaxation in fission and other binary nuclear reactions

      V S Ramamurthy R Ramanna

      More Details Abstract Fulltext PDF

      Mass asymmetry relaxation as manifested in fission and heavy ion-induced binary reactions is reviewed. In fission, the dynamics is characteristic of a fully damped case and is well described by a stochastic theory. In heavy ion deep inelastic collisions and quasi-fission, on the other hand, the relaxation is incomplete giving rise to the possibility of studying its time evolution.

    • Fragment angular distributions in fission and fission-like reactions

      S S Kapoor V S Ramamurthy

      More Details Abstract Fulltext PDF

      Fragment angular distributions in fission is one of the oldest and well understood aspects of fission theory. However, recent heavy ion-induced fission and fission-like reactions have added a new dimension to this problem. We review here our present understanding of the fragment angular distribution theory in fission and fission-like reactions.

    • A novel study of charged carbon clusters using a tandem Van de Graaff accelerator

      V S Ramamurthy D P Mahapatra R T Yadav G V Ravi Prasad Arjun Gopalakrishna

      More Details Abstract Fulltext PDF

      A conventional tandem Van de Graaff accelerator is used to produce charged carbon cluster beams. The unique capability of the method for studying highly charged clusters unaccessible to other methods of producing cluster beams is demonstrated.

    • Leptodermous expansion of nuclear ground state energies and the anomaly in the nuclear curvature energy

      S K Kataria Aruna Nijasure V S Ramamurthy A K Dutta

      More Details Abstract Fulltext PDF

      The leptodermous expansion of the total ground state energy of a nucleus into volume, surface, curvature and gauss curvature contributions has been studied starting from a semi-classical energy density formalism of extended Thomas Fermi type. A numerical procedure was used to obtain the surface energy and curvature energy contributions from surface moments of energy density profilesH(r) for a sequence of nuclei withN=Z and neglecting the coulomb interaction for the three Skyrme forces. A transition to the liquid drop model type expansion in increasing powers ofA−1/3 is then made, taking into account the dependence of the central density and the surface structure on the mass of the nucleus. It is found that there is no inconsistency between the curvature contribution to the total energy in the leptodermous expansion and theA−1/3 term contribution in the liquid drop model expansion. It has been shown that the earlier apparent anomaly between the above two methods arises due to the use of semi-infinite approximation and the mass dependence of the central density and the surface structure of finite nuclei.

  • Pramana – Journal of Physics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.