• S Lokanathan

      Articles written in Pramana – Journal of Physics

    • Transverse momenta of secondaries from 200 GeV/c proton-nucleus interactions

      Y V Keshava Rao R K Puri K B Bhalla S Lokanathan

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      A study of 100 interactions, produced by secondary particles from 200 GeV/c proton interactions in nuclear emulsions, has been made to estimate the transverse momenta of the secondary particles. The data have been analysed by different methods of energy estimation and the weighted average values ofpt have been compared as estimated from various methods. An average value ofpt equal to 0.38 ± 0.03 GeV/c, in proton-nucleus interactions at 200 GeV/c, has been obtained from the production mechanism method.

    • Lattice sum calculations and a Mössbauer study on electric field gradient in phlogopite

      Anjali Krishnamurthy Bipin K Srivastava S Lokanathan

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      Lattice sum contributions have been calculated at the two octahedral sites in a phlogopite mica assuming a systematic distribution of octahedral cationic charges. This, unlike the case of a random distribution of charges, is able to reproduce broad features of quadrupole doublet spectra in Mössbauer experiments suggesting that the doublet assignments in terms of the two structural sites,M1 (trans) andM2(cis), are quite valid. Angle dependence of Mössbauer spectra has also been studied for a ferric-rich phlogopite mica sheet to determine the orientation of the EFG principal axis component and the sign of the quadrupole coupling constant. Quadrupole splitting values and the positive sign of coupling constants match the theoretical predictions quite well but the model fails to predict the observed EFG orientation.

    • Mossbauer study of ferrite systems CoxMn1−xFe2O4 and NixMn1−xFe2O4

      V K Singh N K Khatri S Lokanathan

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      Mössbauer spectra of CoxMn1−xFe2O4 and NixMn1−xFe2O4 ferrites withx values ranging from 0·1 to 0·8 in steps of 0·1 have been recorded at room temperature. All spectra exhibit well-defined Zeeman hyperfine patterns. It has been observed that hyperfine field at Fe3+ nucleus increases more rapidly by nickel substitution than by cobalt substitution. This has been explained in terms of exchange interactions and cation distribution in the spinels. Hyperfine fields, isomer shifts and quadrupole splittings have been determined.

    • A Mössbauer study of hyperfine interaction in the systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4

      V K Singh R Chandra S Lokanathan

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      A Mössbauer study of systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4 for values ofx=0·1, 0·5, 1·0 andy ranging from 0·1 to 2·0 in steps of 0·2 have been made. At room temperature samples fory values ranging in between 0·1 to 0·5 exhibit paramagnetic behaviour while all spectra for values ofy between 0·6 to 0·8 show relaxation effects. Well-defined hyperfine Zeeman spectra are observed for all the samples withy>0·8 and resolved in two sextets corresponding to octahedral and tetrahedral site symmetries and a central doublet probably due to the presence of super-paramagnetic particles in the system. The hyperfine field at57Fe nucleus reduces with decreasing iron cobalt and nickel concentration. These observations have been explained in terms of site preference of cations and exchange interactions.

    • A Mössbauer study of octahedral site symmetries in systems Cox Mn3−xy FeyO4 and NixMn3−xyFeyO4

      V K Singh S Lokanathan

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      A Mössbauer study of cation distribution in systems Cox Mn3−xyFeyO4 and Nix Mn3−xy FeyO4 has been made. It has been found that in both systems all specimens withy<0.6 value exhibit quadrupole doublets corresponding to site symmetries Fe3+(I) and Fe3+(II) of octahedral site. As more and more cobalt or nickel is introduced into the matrix the intensity of the inner quadrupole doublet increases while on introducing iron that of the outer quadrupole doublet increases. After a certain concentration of iron the inner doublet starts becoming more intense. It is suggested that this arises possibly from the substitution of cations in the second co-ordination sphere of Fe3+(I) and Fe3+(II) sites. Fory>0.6 the Mössbauer spectra show relaxation effects.

    • Collective bounce-off phenomenon in139La+Ag(Br) reaction at 1.1 A GeV energy

      B Singh H S Palsania V Kumar K B Bhalla S Lokanathan

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      Out of a total statistics of 896139La+Ag(Br) interactions, 128 interactions having multiplicity of target fragments (Z⩾1)⩾8 and projectile fragments (Z⩾2)⩾4 have been selected. They correspond to quasi-peripheral interactions. Azimuthal angle correlation between sources of target fragments (TFs) and projectile fragments (PFs) shows the existence of bounce-off effect. Using data of La+Ag(Br) and84Kr+Ag(Br) reactions it is shown that individual helium [Z=2, PFs] and heavier fragment [Z⩾3, PFs] show different emission characteristics. Further, a two prong correlation functionTij) plotted for heavier fragments and helium fragments separately, indicates the possibility of existence of different physical conditions. This observation is supported by the different momentum widths of helium fragments and heavier fragments. From the momentum width data of Kr+Ag(Br) reactions normalized density comes out to be ≈4.7. Using quasi-elastic kinematics for the bounce-off nuclei, the excitation energy has been computed from the experimental data of flow angles. The strength of bounce-off seems to decrease with the increase of excitation energy or temperature.

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