• B P SINGH

      Articles written in Pramana – Journal of Physics

    • Effective interactions and charges in58Ni

      S P Pandya B P Singh

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      The structure of the low-lying states of58Ni has been calculated in shell model by assuming an inert56Ni core plus two valence nucleons in the p3/2, f5/2 and p1/2 orbitals. The two-body matrix elements are first expressed in terms of seven radial matrix elements and these are then parametrized to give best fit between the computed and the observed energies of the levels below 4 MeV. The wave-functions obtained using these two-body matrix elements are used to study the concept of effective charges. It is found that a single effective charge is not sufficient to predict theB(E2) rates equally well for the thirteen known transitions for which experimental values are available. Assumption of state-dependent effective charges gives a far better agreement. An analysis using wavefunctions obtained with Kuo’s two-body matrix elements also gives a similar result.

    • Beta-gamma-gamma directional correlation in103Rh

      IVS Rathore B P Singh

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      β-γ-γ directional correlation studies for the cascades (i)β-rays ofEmax=0.12 MeV,γ-rays of 557 keV andγ-rays of 53 keV and (ii)β-rays ofEmax=0.21 MeV,γ-rays of 444 keV andγ-rays of 53 keV have been made. The triple correlation functionsW(θ) were obtained to beW(θ)=1+(−0.153±0.031)P2(cosθ)+(0.004±0.035)P4(cosθ) forβ-rays ofEmax 0.12 MeV→557→53 keV cascade andW(θ)=1+(0.163±0.042)P2(cosθ)+(−0.035±0.058)P4(cosθ) forβ rays ofEmax=0.21 MeV→444 keV→53 keV cascade.

      Spins and parities of the 650, 537 and 93 keV levels of103Rh are deduced by triple angular correlation and the internal conversion coefficient studies. Multipolarities of the transitions are also determined.

    • Negative parity states in144Nd and multipolarity of gamma-transitions from 1 to 2+ states by beta-gamma-gamma angular correlation method

      I V S Rathore B P Singh

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      Some of the low-lying states in many isotopes144Nd,148Sm,152Gd and156Gd show a similar typical behaviour. The first 2+ is regarded as a single quadrupole phonon state and 3 as a single octupole phonon state. The levels with the spins and parities 1, 5, 3, 4, etc. are considered due to the simultaneous excitation of quadrupole and octupole phonons. If this consideration is correct, then the transition fromJ to 2+ states must contain an appreciableE3 content. Theβ-γ-γ angular correlation coefficients for the cascade ofβ-rays ofEmax 800 keV→γ-rays of 1489 keV→γ-rays of 696 keV are used to estimateE3 content inE1 transition in144Nd.

    • Optimization of deconvolution in Compton profile measurements

      V K Agrawal B P Singh

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      The method of generalized least squares has been used to deconvolute the Compton profile measurements in nickel. The method depends on two arbitrary parameters namely the cut-off parameterK and the damping factor λ. This has been discussed and a method suggested to optimize the damping parameter.

    • Measurement and analysis of excitation functions for alpha induced reactions on iodine and cesium

      N P M Sathik M Afzal Ansari B P Singh R Prasad

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      The excitation functions for the reactions127I(α, 2n)129Cs,127I(α, 4n)127Cs,133Cs(α, 2n)135La and133Cs(α, 4n)133La have been measured up to ≈50 MeVα-particle energy using the stacked foil activation technique. Measured excitation functions are compared with pre-equilibrium geometry dependent hybrid model calculations. It has been found that theoretical calculations using an initial exciton numbern0=4 (2p+2n+0h) give good agreement with experimental excitation functions.

    • Synthesis, characterization and third-order nonlinear optical properties of polydiacetylene nanostructures, silver nanoparticles and polydiacetylene–silver nanocomposites

      B BHUSHAN S S TALWAR T KUNDU B P SINGH

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      We have synthesized, characterized and studied the third-order nonlinear optical properties of two different nanostructures of polydiacetylene (PDA), PDA nanocrystals and PDA nanovesicles, along with silver nanoparticles-decorated PDA nanovesicles. The second molecular hyperpolarizability $\gamma (−\omega; \omega,−\omega,\omega$) of the samples has been investigated by antiresonant ring interferometric nonlinear spectroscopic (ARINS) technique using femtosecond mode-locked Ti:sapphire laser in the spectral range of 720–820 nm. The observed spectral dispersion of $\gamma$ has been explained in the framework of three-essential states model and a correlation between the electronic structure and optical nonlinearity of the samples has been established. The energy of two-photon state, transition dipole moments and linewidth of the transitions have been estimated. We have observed that the nonlinear optical properties of PDA nanocrystals and nanovesicles are different because of the influence of chain coupling effects facilitated by the chain packing geometry of the monomers. On the other hand, our investigation reveals that the spectral dispersion characteristic of $\gamma$ for silver nanoparticles-coated PDA nanovesicles is qualitatively similar to that observed for the uncoated PDA nanovesicles but bears no resemblance to that observed in silver nanoparticles. The presence of silver nanoparticles increases the $\gamma$ values of the coated nanovesicles slightly as compared to that of the uncoated nanovesicles, suggesting a definite but weak coupling between the free electrons of the metal nanoparticles and $\pi$ electrons of the polymer in the composite system. Our comparative studies show that the arrangement of polymer chains in polydiacetylene nanocrystals is more favourable for higher nonlinearity.

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