V S Ramamurthy
Articles written in Pramana – Journal of Physics
Volume 5 Issue 3 September 1975 pp 124-143 Nuclear And Particle Physics
Statistical properties of excited fissioning nuclei
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.
Volume 7 Issue 6 December 1976 pp 407-414 Nuclear And Particle Physics
Nuclear level densities in self-consistent field approximation
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.
Volume 8 Issue 4 April 1977 pp 322-327 Nuclear And Particle Physics
Prompt gamma ray multiplicity distributions in spontaneous fission of^{252}Cf
V S Ramamurthy R K Choudhury J O Mohankrishna
The shape parameters of the multiplicity distribution of prompt gamma rays emitted in spontaneous fission of^{252}Cf 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.
Volume 9 Issue 5 November 1977 pp 515-521 Atomic Physics
Search for superheavy elements in monazite from beach sands of South India
S S Kapoor V S Ramamurthy M Lal S K Kataria
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.
Volume 9 Issue 6 December 1977 pp 613-621 Nuclear And Particle Physics
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.
Volume 9 Issue 6 December 1977 pp 623-627 Nuclear And Particle Physics
Multiplicity distribution of prompt gamma rays in spontaneous ternary fission of^{252}Cf
V S Ramamurthy R K Choudhury J C Mohana Krishna
The first and the second moments of the multiplicity distribution of prompt gamma rays in spontaneous ternary fission of^{252}Cf 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%.
Volume 10 Issue 3 March 1978 pp 319-327 Nuclear Physics
Analysis of fission excitation functions and the determination of shell effects at the saddle point
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, (Γ_{f}/Γ_{n})_{1}. The method is applied to the typical case of the fissioning nucleus^{212}Po, formed by alpha bombardment of^{208}Pb. 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 of^{212}Po, 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 parameter
Volume 11 Issue 4 October 1978 pp 457-469 Nuclear And Particle Physics
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.
Volume 20 Issue 6 June 1983 pp 523-546 Nuclear Physics
Classical description of low energy^{16}O +^{16}O collisions
A N Dixit V S Ramamurthy Y R Waghmare
The aim of this paper is to study the scattering of the two ground state^{16}O nuclei, using classical microscopic approach. We have studied fusion cross-section (
Volume 22 Issue 3-4 March 1984 pp 275-282 Nuclear Physics
S S Kapoor V S Ramamurthy R Ramanna
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.
Volume 24 Issue 1-2 January 1985 pp 119-130 Nuclear Physics
Nucleon transport processes in fission and heavy ion reactions
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 of^{235}U, 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.
Volume 27 Issue 5 November 1986 pp 679-684 Nuclear Physics
Surface diffuseness of deformed and rotating nuclei
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.
Volume 33 Issue 1 July 1989 pp 133-144
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.
Volume 33 Issue 1 July 1989 pp 161-174
Fragment angular distributions in fission and fission-like reactions
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.
Volume 39 Issue 5 November 1992 pp 1- Rapid Communication
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
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.
Volume 42 Issue 2 February 1994 pp 107-122
S K Kataria Aruna Nijasure V S Ramamurthy A K Dutta
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 profiles
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