• A P Sharma

      Articles written in Pramana – Journal of Physics

    • Comments on the capture cross-section of electrons in silver bromide grains

      A P Sharma G P Sharma

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      The values in the range of 10−15 cm2 to 10−14 cm2 have been reported by various authors for the capture cross-section of electrons at the traps in silver bromide grains. In this paper we have given a suitable value of this cross-section which is used for computing the track characteristics in nuclear emulsions (e.g. effective ionization, probability of development, grain density and mean gap length) and the ratio of the rate constant of recombination and trapping. Theoretical results agree well with the experimental observations and the available data of other workers and give a convincing support to our choice of this cross-section parameter.

    • Comments on the number of sensitivity centres in silver halide grains

      A P Sharma B P Shukla Vinod Kumar

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      A comment on the number of sensitivity centres in silver halide grains of nuclear emulsions is made and a theory for its evaluation at different temperatures is presented. The results at room temperature agree satisfactorily with assumptions made by various workers.

    • On the formation of silver specks in silver halide crystals

      Mahendra Singh A P Sharma

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      This theoretical study summarizes ionic and electronic processes in AgBr crystals and the influence of its results on photographic process. It deals with the importance of surface generated interstitials which Gurney and Mott left untouched because of the non-availability of sufficient data at that time. The magnitude of various parameters,e.g., mean intra-electron-ion distance in a latent image site, the rate of neutralization of Ag+ ion with trapped electron and capture cross-section for combination of Ag+ ion with the trapped electron, etc. (as desired for understanding the theory of photographic process) are calculated at different temperatures. The results when used in our earlier papers (Singh and Sharma, 1974 and 1975, and Singh 1975) for calculating charged particle track characteristics theoretically were found to give good agreement with the published experimental data (Della Corteet al 1953 and Dyer and Hechman 1967). A model for the mechanism of latent image formation (silver speck) is discussed.

    • An experimental study of angular distribution of fast secondaries in 50 GeV/cπ-Em collisions

      V Kumar S C Varma N S Verma A P Sharma

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      The pseudo-rapidity distribution has been studied for 50 GeV/cπ-colliding with various groups of target nuclei in emulsion. These data are compared with the published data onp-A collisions. It is observed that leading component multiplicity inπ-Em collisions decreases withNh in highη-region. It is also observed that nearly 20% of the interactions proceed via single cluster formation at this projectile energy.

    • Response of photosensitive silver halide micro-crystals to multiple-charged particles

      Mahendra Singh A P Sharma

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      Temperature dependence of sensitivity of silver halide micro-crystals is theoretically examined for a wide range of momenta and charges of ionising particles. Our earlier results on the ionisation theory have now been extended for the interaction of multiple-charged particles with AgBr emulsion grains.

    • Momenta and rapidity characteristics of the multiparticle production in 50 GeV/cπ-Emulsion collison

      V Kumar N S Verma S C Varma A P Sharma

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      The momenta and rapidity characteristics of the particles produced in 50 GeV/cπ-collision with emulsion nuclei have been studied with an emulsion stack exposed under a pulsed magnetic field. The longitudinal rapidity plots suggest that leading pion is attenuated strongly when passing through a heavy nucleus. The average net charge 〈Ns+Ns〉 produced in the final state of the reaction rises rapidly from a negative to a positive value atNh⩽1 and attains a constant value⋍0.60±0.08 at allNh⩾7.

    • A search for superheavy nuclei tracks in extraterrestrial olivine crystals

      J S Yadav A P Sharma G N Flerov V O Perelygin S G Stetsenko P Pellas C Perron R Antanasijevich B Jakupi Y Todorovich

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      A study is made for the search of superheavy nuclei in Marjalahti, Eagle Station and in other pallasite olivines. The olivine crystals are calibrated for heavy ion track lengths by using heavy ion beams from cyclotrons. The calibration for ultra heavy ions which are presently not available with sufficient energy to produce volume tracks in olivine crystals, is based on Katz and Kobetich model of track formation. The length spectrum of volume tracks, revealed by puncturing them with focussed Nd-glass laser beam, is measured and the abundances of different nuclei groups are calculated. Partial annealing has been used at 430°C for 32 hr which eliminates the interfering tracks due to nuclei of atomic numberS ≤ 50. During the scanning 4 cm3 olivine crystals, about 360 long tracks of uranium group as well as two very long tracks have been found. If these tracks belong to superheavy nuclei, the relative abundance of super heavies is found to be 6 × 10−11 in galactic cosmic rays.

    • Plastics as nuclear track detectors for thermal neutron dosimetry

      S M Farid A P Sharma S A Durrani

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      An attempt is made to determine the response of CR-39 and cellulose nitrate plastic track detectors subjected to thermal neutrons. The α-particles are produced from (n, α) reactions in lithium tetraborate convertor placed in contact with different plastics and are recorded in the detectors. The corrected track density gives a fluence sensitivity and dose sensitivity of the order of 10−4 tracks per neutron and 102 tracks/cm2 mrem respectively. A linear relationship is observed between track density and neutron fluence.

    • Study of1840Ar ion tracks in cellulose nitrate

      Subhash Chander Shyam Kumar J S Yadav A P Sharma

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      Sample of cellulose nitrate (Russian) is exposed to1840Ar ions. The bulk etch rate has been studied at different etching temperatures and the activation energy for bulk etch rate has been calculated. The etched track lengths are measured for different etching times. The energy loss rate and range of1840Ar ions in CN(R) is also calculated. The critical threshold value for etchable track in CN(R) is determined by comparing the theoretical and experimental values of track length. The response curve of CN(R) is also presented.

    • Response of Makrofol polycarbonate plastic track detector to 1.1 MeV/N54132Xe-ion

      S M Farid A P Sharma

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      Makrofol polycarbonate plastic track detectors have been exposed to54132Xe -ions of energy 1.1 MeV/N from the cyclotron beam. The bulk etch rate and track etch rate are measured for different temperatures and the activation energies are calculated. The maximum etched track length is compared with the theoretically computed range. The critical energy loss is (dE/dx)c=5 MeV cm2 mg−1 for this detector material.

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