• Y R Waghmare

      Articles written in Pramana – Journal of Physics

    • (π+,p) Reaction in12C

      R S Bhalerao Y R Waghmare

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      Hartree-Fock wave functions obtained from realistic nucleon-nucleon interaction are employed to calculate cross-sections for the reaction12C(π+,p)11C(g.s.). These wave functions take into account central correlations between nucleons inside the nucleus. This itself is found to change the cross-section by more than an order of magnitude. The incoming pion is represented by a plane wave while proton-distortion is taken into account in the high-energy or semi-classical approximation, thereby determining the proton optical well parameters. These values agree well with those obtained by more conventional methods. Variation of the cross-section with the oscillator well parameter is also studied. Calculations have been made using the one-nucleon mechanism for the pion-absorption process.

    • Phenomenological effective interaction for40K

      M Prakash Y R Waghmare

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      Effective interactions of various forms incorporating central, spin-orbit and tensor dependences of two-nucleon potential are parametrized so as to give a satisfactory description of energy levels of40K. These parameters are applied to calculate energy levels of38Cl. Except for the lowest 3 level, the agreement is satisfactory.

    • Microscopic theory of particle-hole states

      Y R Waghmare

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      A self-consistent procedure for calculating the particle-hole states of nuclei is given. This has been applied to the levels of16O nucleus. The particle-hole interaction is derived using Landau theory. The basis states are generated using the Brueckner many-body theory, and used in the random-phase-approximation calculation. The sensitivity of the 3- state at 6.13 MeV with the interaction is discussed, the other states being reasonably insensitive to such a choice. The effect of renormalization of the particle-hole interaction, on various states is also discussed.

    • Effect of correlations on nuclear muon capture

      R Parthasarathy Y R Waghmare

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      The process μ+12C→12B+vμ is studied using the modified Hartree Fock wavefunction obtained with the unitary-model-operator-approach starting from the realistic hardcore nucleon-nucleon interaction, with the aim of testing the wavefunctions and obtaining a numerical value for the induced pseudoscalar coupling constant (gP). These observables, namely, the partial capture rate to the12B(1+; g.s), its recoil nuclear polarisation and the total capture rate, which exhaust the available experimental data in the above process have been calculated and compared with the other theoretical and experimental results.

      As far as the partial capture rate is concerned the use of the unitary-model operator approach wave functions for12C withb=2.09 fm and Cohen-Kurath wave function for12B(1+; g.s) reduces the pure shell model capture rate by about 30%. The effect of strong configuration mixing in the ground state of12C in taken into account by introducing a scale factor ξ similar to the ‘amplitude reduction factor’ of Donnelly and Walecka. With this ξ the agreement with the experiment both for the partial capture rate and the beta decay ‘ft’ value is found to be satisfactory.

      The12B(1+; g.s) recoil polarisation is found to be insensitive to the use of the unitary-model-operator-approach wave functions. When compared with the experimental data, we obtaingP=(14.9±1.9)gA.

      The total capture rate is found to be sensitive to the use of the unitary-modeloperator-approach wave functions which contain the effect of nucleon-nucleon short range correlations and we obtain a satisfactory agreement with the experiment for16O and12C, thereby revealing the importance of the effect of such correlations in the total capture rate studies.

    • Classical description of low energy16O +16O collisions

      A N Dixit V S Ramamurthy Y R Waghmare

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      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.

    • A study of pion absorption by16O using realistic interactions—I. Twonucleon emission following bound-pion absorption

      U N L Mathur Y R Waghmare

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      Matrix element of the Galilean invariant non-relativistic reduction of the pseudoscalar-pseudovector interaction has been calculated assuming the reaction to be a direct process with boundπ being absorbed by a correlated pair of nucleons. The Hartree-Fock wavefunctions obtained with the unitary-model-operator approach starting with the realistic nucleon-nucleon interaction have been used forπ-capturing nucleon pair in the initial state. The calculations have been done with and without antisymmetrising the initial state wavefunction of the pion absorbing pair. For the final state nucleon-nucleon interaction has been taken into account. The strongπ-nucleus interaction together with the Coulomb interaction with the finite nuclear size on the bound pion wavefunction are taken into account. Angular distributions of the emitted nucleon-pair, the branching ratios and the total absorption rates are calculated for16O with and without antisymmetrisation effect. The calculated results are compared with the experimental and other theoretical work.

    • Pion absorption by16O using realistic interactions—II: Free pion absorption followed by emission of proton

      U N L Mathur Y R Waghmare

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      Matrix element of the Gallilean invariant nonrelativistic reduction of the pseudoscalar-pseudovector interaction has been calculated for free pion absorption by a single nucleon inside the nucleus of16O. The Hartree-Fock wavefunctions obtained with the unitary-model-operator approach starting with the hard-core nucleon-nucleon interaction have been used for the π-capturing nucleon in the initial state. The initial pion distortion in the presence of nuclear field of the absorbing nucleus prior to its absorption together with the Coulomb interaction with the finite nuclear size has been taken into account. The distortion of the emitted proton in the field of the residual nucleus has also been considered. The differential cross-sections have been obtained and calculated results are compared with the previous experimental and theoretical work.

    • Muon capture by16O—using a microscopic theory of particle-hole states

      V N Sridhar R Parthasarathy Y R Waghmare

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      The partial capture rates for the process,μ +16O (g·s) →16N (2, 1, 0, 3) +vμ have been calculated using the particle-hole wavefunctions obtained using self-consistent procedure. In deriving these wavefunctions, the effectiveN-N interaction has been constructed from the bare Hamada-Johnston interaction. The terms in the muon capture Hamiltonian that depend on the momentum of the capturing proton have been included and their importance in 0+ → 0 transition is exhibited. The agreement with the available experimental data is good. The need to incorporate meson exchange effects in 0+ → 0 transition is pointed out.

    • Heavy-ion fusion cross-section calculations in classical microscopic equations of motion approach

      S S Godre Y R Waghmare

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      Fusion cross-sections for16O +16O reaction earlier calculated in classical microscopic equations of motion approach, with Lennard-Jones form ofNN interaction potential are overestimated compared to the experimental data at lower energies. This large deviation was attributed to possible break down of classical approximations at lower energies. The aim of this paper is to show that this discrepancy was rather due to certain assumptions made in the specification of initial conditions; in particular due to neglect of Coulomb interaction between the colliding ions at far off distances. Use of Lennard-Jones potential is also critically examined.

    • Heavy-ion fusion in classical and semiclassical microscopic approaches

      S S Godre Y R Waghmare

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      Classical and semi-classical microscopic approaches leading to fusion of two heavy nuclei are studied. Calculations show that the results depend strongly on the nature of the nucleon-nucleon interaction. It is also observed that there is no angular momentum window unlike in TDHF calculations.

    • A possible mechanism of cold fusion

      J K Bhattacharjee L Satpathy Y R Waghmare

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      A possible mechanism for the occurrence of nuclear fusion at room temperature is presented. Neutralization of the positive charge of the deuteron nucleus by its orbiting electron due to large enhancement of effective mass results in the vanishing of the Coulomb barrier which facilitates fusion at room temperature.

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