• S Kailas

      Articles written in Pramana – Journal of Physics

    • 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.

    • 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.

    • Elastic scattering of 36 MeV alpha particles from197Au

      S Kailas S K Gupta S Bhattacharya S N Chintalapudi Y P Viyogi

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      Angular distribution for the elastic scattering of 36 MeV alpha particles from gold target has been measured fromϑ ∼ 10–56°. The cross-section data have been analyzed in terms of the optical model. The real part of the optical model potential (VR) has been deduced by two prescriptions: (i) combining the volume integral, the radius at whichVR=2.4 MeV and the slope at this radius (1/VR) (dVR/dr) (ii) combining the volume integral, the root mean square radius and the equivalent sharp radius systematics. The imaginary potential depth has been searched to fit the data. The prediction using (i) for the real potential fits the data the best.

    • 51(p, n)51Cr reaction from Ep 1.9 to 4.5 MeV

      S Kailas S K Gupta S S Kerekatte C V Fernandes

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      The total cross-section for the reaction51V(p, n)51Cr has been measured fromEp 1.9 to 4.5 MeV by using two different techniques: (i) by detecting the neutron using the 4π neutron counter and (ii) by measuring the activity of the residual nucleus51Cr. The two measurements are consistent with each other and together they are in good agreement with the data of Zyskindet al. The thermonuclear reaction rates have also been extracted starting from these cross-sections.

    • 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.

    • Elastic and inelastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb

      P P Singh Q Li P Schwandt W W Jacobs M Saber E J Stephenson A Saxena S Kailas

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      Differential cross-section angular distributions for the elastic scattering of 270 MeV3He particles from58Ni,90Zr,116Sn and208Pb have been measured. Optical model analysis of the cross-sections has yielded the optical model parameters for3He particles at 270 MeV. Angular distributions have also been measured for the inelastic excitation of the low-lying levels in the above mentioned nuclei. A collective model analysis using the distorted wave Born approximation (DWBA) of these cross-sections with the distorted waves generated by the optical model parameters determined from the elastic scattering analysis, has yielded the reduced transition probability (B(EL)) values consistent with those reported in the literature.

    • Giant resonances in90Zr and116Sn

      S Kailas A Saxena P P Singh Q Chen D L Friesel P Schwandt E J Stephenson

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      The giant resonance region in90Zr and116Sn excited by 270 MeV helions has been measured up to about 35 MeV excitation energy. The low and the high energy octupole resonances are seen prominently in addition to the quadrupole and the monopole resonances. The angular distribution data for the various multipoles are satisfactorily explained by the collective model calculations. The percentatge energy weighted sum rule strengths have been determined for all the prominent resonances.

    • Fusion cross section for the system6Li+28Si atE ∼ 36 MeV

      S Kailas R Vandenbosch A Charlop A Garcia S Gil S J Luke B McLain D Prindle

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      The fusion cross section for the system6Li+28Si has been measured atE∼36 MeV. Combining this with the data available at lower energies, the nucleus-nucleus real potentials have been determined for a range of interaction distances.

    • Neutron flow or collective degrees of freedom for near barrier heavy-ion fusion

      S Kailas A Navin

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      Various models have been proposed in order to understand the near barrier heavy-ion fusion data. Amongst others the coupled channel approach of Dasso and Landowne and the neutron flow picture of Stelson are two of the mechanisms which describe well a large body of near barrier fusion data. From an analysis of16O induced fusion reaction around the barrier for various targets an attempt has been made to identify which out of the above two mechanisms is more appropriate to explain these data.

    • Sub-barrier fission fragment angular distributions for the system19F+232Th

      S Kailas A Navin A Chatterjee P Singh A Saxena D M Nadkarni D C Biswas R K Choudhury S S Kapoor

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      The measurements of fission fragment angular distributions for the system19F+232Th have been extended to the sub-barrier energies of 89.3, 91.5 and 93.6 MeV. The measured anisotropies, within errors are nearly the same over this energy region. However, the deviation of the experimental values of anisotropies from that of standard statistical model predictions increases as the bombarding energy is lowered.

    • Heavy-ion induced fission reactions at near-barrier energies — what have we learnt?

      S Kailas

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      Systematic studies of heavy-ion induced fission reactions at near-barrier energies carried out in the last decade have brought out many interesting aspects of fission process in general. The recent experimental findings which show dependence of fission fragment angular distributions on entrance channel, shape, size and spin of the interacting nuclei and shell closure of the intermediate compound nucleus are summarised in the present paper.

    • Nuclear orbiting and anomalies in nuclear reactions

      A De A Mitra A Ray SR Banerjee M Sengupta A Chatterjee S Kailas HS Patel MG Betigiri SK Dutta

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      In this paper, we report our measurements of back-angle oxygen and carbon particle yields from 16O+89Y, 12C+93Nb reactions forming the same compound nucleus 105Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence at high excitation energies from 16O+89Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission is also discussed.

    • Light charged particle emission in heavy-ion reactions — What have we learnt?

      S Kailas

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      Light charged particles emitted in heavy-ion induced reactions, their spectra and angular distributions measured over a range of energies, carry the signature of the underlying reaction mechanisms. Analysis of data of light charged particles, both inclusive and exclusive measured in coincidence with gamma rays, fission products, evaporation residues have yielded interesting results which bring out the influence of nuclear structure, nuclear mean field and dynamics on the emission of these particles.

    • Breakup of 42 MeV 7Li projectiles in the fields of 12C and 197Au nuclei

      Dhruba Gupta C Samanta R Kanungo P Basu Subinit Roy S Kailas A Chatterjee B J Roy K Mahata A Samant A Shrivastava

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      Inclusive cross sections of α particles and tritons from the breakup of 42 MeV 7Li by 12C and 197Au targets are presented and analysed in the framework of the Serber model. Spectral distortions due to the targets and relevant reaction mechanisms are discussed.

    • Status report on the folded tandem ion accelerator at BARC

      P Singh S K Gupta M J Kansara A Agarwal S Santra Rajesh Kumar A Basu P Sapna S P Sarode N B V Subrahmanyam J P Bhatt P J Raut S S Pol P V Bhagwat S Kailas B K Jain

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      The folded tandem ion accelerator (FOTIA) facility set up at BARC has become operational. At present, it is used for elemental analysis studies using the Rutherford backscattering technique. The beams of1H, 7Li, 12C, 16O and 19F have been accelerated up to terminal voltages of about 3 MV and are available for experiments. The terminal voltage is stable within ±2 kV. In this paper, present status of the FOTIA and future plans are discussed.

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