• M K Mehta

      Articles written in Pramana – Journal of Physics

    • Spectroscopy of50V with (p, nγ) reaction

      S K Gupta S Saini L V Namjoshi M K Mehta

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      Information on the low-lying levels up to ∼1.9 MeV excitation of the doubly odd nucleus50V has been obtained through the Ge (Li)-Ge (Li) coincidence study with the50Ti(p, nγ)50V reaction. Branching ratios have been measured and tentative spin-parity assignments have been made. A detailed comparison with other measurements reported recently has also been made. Using the lowest seniority wave functions with (f7/2)p3 (f7/2)n−1 configuration, energy levels and electromagnetic properties have been calculated. These have been compared with the present and earlier experimental data.

    • Thermonuclear reaction rates from (p, n) reactions

      S Kailas M K Mehta

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      Thermonuclear reaction rates for the temperature range 1≤T9≤5 have been extracted from experimentally measured (p, n) cross sections for45Sc50Ti,51V,54Cr,55Mn and59Co nuclides below 5 MeV bombarding energy. These reaction rates are important in the build-up of medium and heavy nuclides in the stellar evolution process and nucleosynthesis. To enhance the usefulness of these reaction rates in astrophysical calculations, they have been fitted to an analytic function of temperature, valid throughout the temperature range considered here.

    • Total (p, n) reaction cross section study on51V over the incident energy range 1·56 to 5·53 MeV

      M K Mehta S Kailas K K Sekharan

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      The total (p, n) reaction cross section for51V has been measured as a function of proton energy in the energy range 1·56 to 5·53 MeV with thick and thin targets. The fluctuations in the fine resolution excitation functions were analysed, to extract 〈Γ〉, the coherence width. The thick target excitation function suitably averaged over appropriate energy intervals has been compared with the optical model, Hauser-Feshbach and Hauser-Feshbach-Moldauer calculations. The strong isobaric analog resonance atEp ∼ 2·340 has been shape analysed to extract the proton width Γp, the spreading withW and the spectroscopic factor.

    • A study of the reaction19F(α, n)22Na in the bombarding energy range 2·6 to 5·1 MeV

      M Balakrishnan S Kailas M K Mehta

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      The total (α, n) reaction cross section for19F has been measured as a function of alpha energy in the energy range 2·6 to 5·1 MeV with a thin target. The excitation function exhibits a large number of resonances. The prominent amongst these for which theJπ values are known have been analysed to extract the partial widthsΓα and Γn. Statistical analysis of the data in terms of strength function and average level spacing distribution has also been performed.

    • Mass absorption coefficients and range of beta particles in Be, Al, Cu, Ag and Pb

      Nathu Ram I S Sundara Rao M K Mehta

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      It is demonstrated that the practical range of a beta spectrum (Emax=E) in any material can be obtained from mass absorption coefficient (μ/ρ) values. It is further shown that a semiempirical relation likeμ/ρ =AE−B in whichA andB are related to the atomic numberZ, of the absorber can be used for determiningμ/ρ of any material of known atomic numberZ. Theβ particle ranges are compared with theoreticalcsda and practical ranges from literature.

    • Two million volt terminal tandem accelerator

      M G Betigeri T P David S C Hiremath P K Iyengar M K Mehta V S Raju P Singh J N Soni

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      Design and construction details of a horizontal 2 MV Tandem Van de Graaff accelerator built at Bhabha Atomic Research Centre are given. A terminal voltage of 2.15 MV has been achieved. Energy analysed Corona stabilized beams of protons and oxygen ions have been obtained. Experiments have been carried out to test the performance of the accelerator.

    • Reaction48Ca (p, n)48Sc fromEp=1.885 to 5.1 MeV

      Gulzar Singh S Kailas S Saini A Chatterjee M Balakrishnan M K Mehta

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      The total (p, n) reaction cross section for48Ca has been measured as a function of proton energy in the energy range 1.885 to 5.100 MeV with an overall resolution of ∼ 2 keV and in ∼ 5 keV energy steps. The fluctutions in fine resolution data have been analysed to determine the average coherence width 〈Γ〉. The excitation function averaged over large energy intervals has been analyzed in terms of the optical model. The isobaric analogue resonances atEp ∼ 1.95 and 4 MeV have been shape-analyzed to extract the proton partial width and the spectroscopic factorSn. A comparison of the gross structures observed in ∼ 55 keV averaged excitation function with the predictions of Izumo’s partial equilibrium model has also been made.

    • Proton-nucleus optical model potential at low energies—a review

      M K Mehta S Kailas

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      Ever since it was proposed more than three decades ago, the nuclear optical model has been very successful in interpreting a large body of nucleon-induced nuclear reaction data in terms of a complex nucleon-nucleus potential. Rapid progress both in the experimental measurements and the theoretical developments in the last two decades has led to a better understanding of this nucleon-nucleus optical potential. From the parameter-fitting phenomenological stage, the optical model has come a long way and it is now possible to calculate the nucleon-nucleus optical potential in a reasonable way starting from the fundamental nucleon-nucleon interaction. Excellent reviews on various aspects of the optical model exist in the literature for proton energies above 10 MeV. The present article is an attempt to review comprehensively the status of the proton-nucleus optical potential at low proton energies, below the Coulomb-barrier, for target nuclei with mass numbers lying between 40 and 130. The sets of phenomenological optical potential derived mostly from (p, n) reaction data are reviewed and their applicabilities discussed. The neutron-nucleus optical model is referred to wherever it is relevant. Microscopic calculations for one case is carried out and compared with the corresponding phenomenological values.

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