• A Roy

      Articles written in Pramana – Journal of Physics

    • Study of analogue states in52Cr through proton capture by51V

      A Roy K V K Iyengar M L Jhingan S K Bhattacherjee

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      γ-Ray yield function has been studied for the proton capture by vanadium in the proton energy range 720–1300 keV. Isobaric analogues of low lying states in52V have been identified. At two resonances theγ-decay andγ-ray angular distributions have been obtained and the branching ratios and the multipole mixing ratios have been deduced. The analogue-antianalogue M1 transition in52Cr is found to be strongly hindered as in other f7/2 nuclei. TheQ-value obtained for this reaction is (10500±2.8) keV and the Coulomb displacement energy is (8.06±0.01) MeV. An upper limit of 2 meV has been obtained for theα- decay strength of the 11.395 MeV state in52Cr.

    • A search for colour van der Waals interaction

      C V K Baba A Roy

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      It is suggested that the strength of nuclear colour van der Waals interaction, if present, can be determined by measuring deviations from Rutherford scattering of charged hadrons from nuclei, at energies well below the Coulomb barrier. Experimental limit on the strength of such a potential is obtained asλ<50, when the colour van der Waals potential is given byV(r)=λ(hc/r0)(r0/r)7, withr0, the scaling length, taken as 1 fm. This limit is obtained from an analysis of existing experiments and by performing scattering experiments of 3–4.6 MeV protons from a208Pb target.

    • An experimental limit on the coupling of a light neutral pseudoscalar particle to hadrons

      D Indumathi C V K Baba A Roy S C Vaidya

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      Detailed results of an experiment, looking for a short-lived neutral particle decaying by ane+e pair in the decay of the 3.68 MeV (3/2) state in13C, whose decay is predominantly M1, are presented. An upper limit of 7 × 10−5 has been placed on the branching ratio for decay through such a particle with a mass in the range 1.7 to 1.9 MeV/c2. This leads to an upper limit of 10−6 for the coupling of such a particle to nucleons. Such a limit rules out the explanation of thee+ ande peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.

    • Four quasi-particle level at 2256 keV in182Re

      Y K Agarwal C V K Baba D Bhattacharya S K Bhattacherjee R K Bhowmik V M Datar H C Jain A Roy

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      In-beam nuclear spectroscopic studies of182Re, following the reaction181Ta(α, 3n)182Re have been made using gamma-ray and internal conversion electron techniques.K-conversion coefficients for several transitions have been measured and the multi-polarities of the various transitions assigned. In particular, the spin and parity of the four-quasi-particle isomeric level at 2256 keV were determined to be 16. Theg-factor of this level has been measured to beg = 0·32 ± 0·05. On the basis of theg-factor and the decay pattern of this level, a configuration {v9/2+ [624↑]v7/2 [514↓]v7/2 [503↑]π9/2 [514↑]}kx = 16 has been assigned to this level. The nature of the retardation of the gamma transitions deexciting this level is discussed. It is argued that the measured retardation factors can be explained if the nucleus has a triaxial shape.

    • 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.

    • 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.

    • A plunger set-up for measuring picosecond nuclear half-lives

      H C Jain S Chattopadhyay Y K Agarwal M L Jhingan S K Mitra H V Panchal A Roy

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      A plunger set-up has been designed and constructed to measure picosecond nuclear half-lives using recoil distance method (RDM). The system has been used to measure the half-lives of nuclear states in35Cl,37,38Ar and40K. The shortest half-life measured with the system isT1/2=0.36(14) ps for the 4366 keV (8+) state and the longest half-life isT1/2=1.10(7) ns for the 2543 keV (7+) state in40K.

    • Yields of evaporation residues and average angular momentum in heavy ion induced fusion reactions leading to compound nucleus96Ru

      M Dasgupta A Navin Y K Agarwal C V K Baba H C Jain M L Jhingan A Roy

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      Cross-sections for production of evaporation residues from the compound nucleus96Ru* formed by fusion reactions28Si+68Zn,32S+64Ni,37Cl+59Co and45Sc+51V have been obtained from the yields of their characteristicγ-rays. The measurements span an excitation energy range of 55 MeV to 70 MeV of the compound nucleus. The evaporation residue (ER) cross-sections have been analysed in terms of statistical model for the decay of the compound nucleus. A good agreement is found between statistical model calculation and the experimental evaporation residue cross-sections in all the four cases. It is shown that the average angular momentum$$\bar \ell $$ of the compound nucleus can be deduced from a comparison of the experimentally measured and the statistical model predictions for the ER cross-sections. The validity of this method of deriving$$\bar \ell $$ has been discussed for the case of16O+154Sm system.

    • Propagation of waves in a multicomponent plasma having charged dust particles

      Sukanya Burman A Roy Chowdhury S N Paul

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      Propagation of both low and high frequency waves in a plasma consisting of electrons, ions, positrons and charged dust particles have been theoretically studied. The characteristics of dust acoustic wave propagating through the plasma has been analysed and the dispersion relation deduced is a generalization of that obtained by previous authors. It is found that nonlinear localization of high frequency electromagnetic field in such a plasma generates magnetic field. This magnetic field is seen to depend on the temperatures of electrons and positrons and also on their equilibrium density ratio. It is suggested that the present model would be applicable to find the magnetic field generation in space plasma.

    • ECR ion source based low energy ion beam facility

      P Kumar G Rodrigues U K Rao C P Safvan D Kanjilal A Roy

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      Mass analyzed highly charged ion beams of energy ranging from a few keV to a few MeV plays an important role in various aspects of research in modern physics. In this paper a unique low energy ion beam facility (LEIBF) set up at Nuclear Science Centre (NSC) for providing low and medium energy multiply charged ion beams ranging from a few keV to a few MeV for research in materials sciences, atomic and molecular physics is described. One of the important features of this facility is the availability of relatively large currents of multiply charged positive ions from an electron cyclotron resonance (ECR) source placed entirely on a high voltage platform. All the electronic and vacuum systems related to the ECR source including 10 GHz ultra high frequency (UHF) transmitter, high voltage power supplies for extractor and Einzel lens are placed on a high voltage platform. All the equipments are controlled using a personal computer at ground potential through optical fibers for high voltage isolation. Some of the experimental facilities available are also described.

    • Superconducting linear accelerator system for NSC

      P N Prakash T S Datta B P Ajith Kumar J Antony P Barua J Chacko A Choudhury G K Chadhari S Ghosh S Kar S A Krishnan Manoj Kumar Rajesh Kumar A Mandal D S Mathuria R S Meena R Mehta K K Mistri A Pandey M V Suresh Babu B K Sahu A Sarkar S S K Sonti A Rai S Venkatramanan J Zacharias R K Bhowmik A Roy

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      This paper reports the construction of a superconducting linear accelerator as a booster to the 15 UD Pelletron accelerator at Nuclear Science Centre, New Delhi. The LINAC will use superconducting niobium quarter wave resonators as the accelerating element. Construction of the linear accelerator has progressed sufficiently. Details of the entire accelerator system including the cryogenics facility, RF electronics development, facilities for fabricating niobium resonators indigenously, and present status of the project are presented.

    • First on-line test of the LINAC superbuncher at nuclear science centre

      S Ghosh R Mehta P N Prakash A Mandal G K Chaudhari S S K Sonti D S Mathuria K K Mistry A Rai S Rao P Barua A Pandey B K Sahu A Sarkar G Joshi S K Datta R K Bhowmik A Roy

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      An on-line test of the LINAC superbuncher at Nuclear Science Centre has been successfully performed. DC O7+ beam of nominal energy 92 MeV was accelerated through the superbuncher resonator, operating at a field of 4.54 MV/m. The total energy gain of the beam was measured to be 4.5 MeV. For the pulsed beam test a phase locked bunched beam of O7+ of nominal energy 92 MeV, FWHM 1.3 ns from the pre-tandem multiharmonic buncher was injected into the superbuncher. By properly adjusting the phase and amplitude of the resonator, the best FWHM of the bunched beam was measured to be 185 ps near the entrance of the first LINAC module. Fully depleted cooled surface barrier detector was used for measuring the time width. In a separate experiment the intrinsic time resolution of the same detector was measured to be 134 ps. Consequently the intrinsic time width of the bunched beam, after correcting for the detector resolution, would be 127 ps. Details of the experiment and results are presented.

    • Solitary wave and modulational instability in a strongly coupled semiclassical relativistic dusty pair plasma with density gradient


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      Using a set of fluid equations to describe the inertial dust grain component in a dense collisionless unmagnetised plasma under the influence of weakly relativistic semiclassical electrons and positrons, the propagation of dust-acoustic wave is studied in the strong coupling regime when the dust density is non-uniform.Our main aim is to analyse the role of semiclassical and relativistic environment (frequently encountered in astrophysical context) on various features of strongly coupled dusty plasma. The semiclassical environment of the electrons and positrons is assumed to be described by the Chandrasekhar equation of state. Our second aim is to see the effect of spatial variation of the dust equilibrium density, which is known to occur due to the deformation of the Debye sheath which in turn leads to polarisation force.Anew type of nonlinear Schrödinger equation with spatially varying coefficient is deduced and its modulational stability is studied in detail. In the last section, we have taken recourse to Madelung picture to deduce a variable coefficient Korteweg–de Vries equation from this new nonlinear Schrödinger equation.

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