• Volume 35, Issue 1

      July 1990,   pages  1-114

    • On the discontinuities in the energy spectrum of a model Hamiltonian

      R K Pandey V S Varma

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      The occurrence of discontinuities in the energy spectrum of thes-wave Hamiltonian in three dimensionsH(μ, λ) =p2/2 − 1/r + 2µr + 2λ2r2 has been reported by us. In this communication we develop a unified understanding, based principally on the topography of the energy surfaces, of the different discontinuities we reported earlier. These discontinuities do not in general occur wherever the corresponding classical system would display catastrophic behaviour.

    • Regge behaviour at high energy and more on boson-fermion interaction

      A Roy Chowdhury B Sidhanta

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      Our approach to the problem of boson-fermion interaction in the conventional RFT stems from a model of super-symmetric version in 2-space and 1 time world. Basically it is stressed here that at super high energy there may not be any distinction between the bosonic and fermionic modes and may be treated on a common footing. Usual renormalization group approach for the vertex function has been adopted and the characteristic functionsβ1 andβ2 are calculated and the possibility of having stable points in the theory has been studied.

    • Static baryon properties in a relativistic quark model with centre-of-mass correction

      S N Jena S Panda

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      The static properties such as magnetic moments, charge radii and axial vector coupling constant ratios of the quark core of baryons in the nucleon octet have been calculated in an independent-quark model based on the Dirac equation with equally mixed scalar-vector potential in linear form in the current quark mass limit. The results obtained with appropriate corrections due to centre-of-mass motion are in reasonable agreement with experimental data. The magnetic moments of the quark core of baryons in the charmed andb-flavoured sectors have also been calculated with this model and the overall predictions so obtained compare very well with other model predictions.

    • Model of confinement

      S Biswas S Kumar L Das

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      Confinement model for quarks and gluons is formulated. An attempt has been made to derive the dielectric function starting from a Lagrangian that also determines the quark and gluon field equations. Deconfinement mechanism is also discussed.

    • A multi NaI(Tl) detector array for medium energyγ-ray spectroscopy

      Y K Agarwal C V K Baba D R Chakrabarty V M Datar D A Gothe H C Jain A Roy M K Sharan

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      An array of seven hexagonal NaI(Tl) detectors has been set up for measuringγ-ray spectra in the energy region 5 MeV ≤Eγ ≤ 40 MeV with good accuracy. This is in contrast to earlier set ups which mostly used one large sized (about 10 inchesφ × 15 inches long)NaI(Tl) detector. This set up has been made for the study ofγ decay of GDR based on high spin states and ultra-dipole radiations.

      The array has been provided with the following features: a) TOF discrimination against neutrons, b) pile up detection and elimination, c) active and passive shielding to cut down background and d) an array of trigger counters for multiplicity dependence measurements. The well known program EGS4 has been used to determine the response of the array forγ-rays in the energy region 5–40 MeV and several test measurements have been carried out to confirm the validity of the calculated response functions. Some typicalγ-ray spectra fromα and16O induced reactions measured at VECC, Calcutta and Pelletron accelerator at TIFR are also shown.

    • On πd elastic scattering using aligned deuteron targets

      A Sudha Rao G Ramachandran

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      A theoretical study is made of the advantages to be gained in polarizing a deuteron target by applying an external electric quadrupole field with non-zero asymmetry parameter for carrying outd(π, π)d experiments, in order to determine empirically the helicity amplitudes A, B, C, D characterizing the scattering, without any phase ambiguities.

    • General transient solutions for the four-coupled Bloch-type equations for a two-level system

      J B Shinde S C Mehrotra

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      When the collisional dynamics of two states under consideration for a radiative transition is different, the polarization and population relaxations in gas phase at low pressure are governed by four-, instead of three-, coupled Bloch-type equations. The general transient solutions of these four-coupled equations are solved by using the Laplace transformation technique. It has been found that an additional exponential term appears because of the effect. This is also responsible for the non-exponential character in the decay signal of a transient microwave pulse experiment, besides other factors reported earlier.

    • Inner-shell excitation of alkali-metal atoms

      S N Tiwary

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      Inner-shell excitation of alkali-metal atoms, which leads to auto-ionization, is investigated. Comparison is made with other available data. Basic difficulties in making accurate calculations for inner-shell excitation process are discussed. Suggestions are made for further study of inner-shell process in atoms and ions.

    • Three photon resonant ionization in atomic potassium via S, P, D and F series Rydberg states

      A Sharma G L Bhale M A N Razvi

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      Single colour three photon resonant ionization (2 + 1) is observed in atomic potassium vapour in a heat pipe oven using an excimer laser pumped dye laser. Using wavelengths between 570 nm and 603 nm various2S and2D Rydberg states are populated by two photon excitation. Third photon of the same wavelength ionizes the atoms. Rydberg states up ton ⋍ 50 are observed. Electric field as low as 1 V/cm causes extensive Stark mixing of the states. This results in progressively higher three photon ionization signals via the perturbed2P and2F Rydberg states. The three photon ionization process is studied using both linearly and circularly polarized incident light. The experiment shows qualitatively that the2P Rydberg states are perturbed primarily by the2D states in the prescence of an external electric field and to a much smaller extent by2S states. This is also explained theoretically by calculating the Stark mixing coefficients under the Bates and Daamgard (1949) approximation. Implication for a similar effect in other alkali elements is discussed.

    • Experimental investigation of angular dependence of photon induced L-shell X-ray emission intensity

      K S Kahlon K Shatendra K L Allawadhi B S Sood

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      The angular dependence of emission intensity of L shell X-rays induced by 59.57 keV photons in Pb and U is investigated by measuring the normalized intensities of the resolved L X-ray peaks at different angles varying from 40° to 120°. It is observed that while Ll and Lα X-ray peaks (originating fromJ = 3/2 state) show some anisotropic angular distribution, the emission of Lβ and Lγ X-ray peaks is isotropic. The present results contradict the calculations of Co-oper and Zare (1969) that after photoionization of inner shell, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic but confirm the predictions of Fluggeet al (1972) that the atomic inner shell vacancies produced after photoionization are aligned and the x-ray emission from the filling of vacancies in state withJ ⩾ 3/2 is anisotropic.

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