• Volume 12, Issue 5

      May 1979,   pages  427-563

    • Alpha particle scattering in the rigid projectile approximation

      Jayati Ghosh V S Varma

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      We study elastic α-particle scattering offp,α-particle and12C targets at 17.9 GeV/c incident momentum in the rigid projectile approximation of the Glauber model. Differential and total cross-sections are computed and compared with the data. Reasonable agreement with the observed differential cross-sections is found for small momentum transfers but short-range dynamical correlations in the target will probably have to be taken into account to get better agreement at larger momentum transfers, particularly in the case of α-12C scattering.

    • A search for rare types of fission induced in silver and bromine nuclei

      K Bhattacharya T D Goswami

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      Ternary and quaternary fission produced in silver and bromine nuclei have been studied withK5 nuclear emulsion exposed to 1.8 GeV/cK beams. The frequency of the ternary events is found to be ∼0.08 of that of the binary events produced in the same volume of the emulsion. The range ratio and range distribution of the fission fragments are studied and the angles between each pair of the fragments are determined. Ranges are found to vary from 5 to 40µ with a maximum number lying between 5 and 10µ. The angles between the fission fragments are found to form a broad distribution extending from 40° to 180°. A few of the events have also been analysed to give them a possible identity. A possible case of quaternary fission has also been reported.

    • Long range interactions between some charged solitons

      M Raj Lakshmi

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      A procedure is offered for evaluating the forces between classical, charged solitons at large distances. This is employed for the solitons of a complex, scalar two-dimensional field theory with a U(1) symmetry, that leads to a conserved chargeQ. These forces are the analogues of the strong interaction forces. The potential,U(Q, R), is found to be attractive, of long range, and strong when the coupling constants in the theory are small. The dependence ofU(Q, R) onQ, the sum of the charges of the two interacting solitons (Q will refer to isospin in the SU(2) generalisation of the U(1) symmetric theory) is of importance in the theory of strong interactions; group theoretical considerations do not give such information. The interaction obtained here will be the leading term in the corresponding quantum field theory when the coupling-constants are small.

    • Iodine stabilised He-Ne Laser

      V D Dandwate P N Puntambekar D Sen

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      A single mode He-Ne laser operating at 6328 Å is used with an iodine cell in the cavity to detect the absorption components of iodine falling within the gain curve of the laser line. Experimental details are given for locking the frequency of the laser line with one of the hyperfine components of the iodine absorption line, using a servo-control system. The system uses the technique of detecting the first and third harmonics of the modulation frequency.

    • Exact solutions of Dirac equation

      S V Kulkarni L K Sharma

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      In this paper Dirac equation for two electromagnetic potentials viz vector potential and scalar potential have been solved. These solutions of the Dirac equation are written in terms of known solutions of the Schrödinger equation. The presentation is within the two-component relativistic description. Mainly the bound state solutions have been obtained.

    • Power spectrum of density fluctuations in a finite reactive-diffusive system: resistance fluctuation spectroscopy

      V Balakrishnan N K Bansal

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      The measurement in thermal equilibrium of the vacancy contribution to the residual resistivity of metals has posed certain difficulties. The recent experiment of Celasco and co-workers represents a new, powerful approach to this problem, via the measurement of the power spectrum of the voltage noise generated by resistivity fluctuations. The latter originate in vacancy number fluctuations. We develop a theory for the power spectrum, incorporating three basic features. Vacancies can be annihilated in the material and they diffuse. Grain boundaries act as sources and sinks for vacancies. Both annihilation (a form of reaction) and diffusion are noisy processes. We therefore set up and solve a reactive-diffusive stochastic equation for the instantaneous density, with appropriatefinite boundary conditions. Assuming for simplicity that the grains are spherical, the power spectrum is evaluated exactly, in closed form. A detailed comparison with experiment is made. The physical origins of different time scales in the problem and the consequent frequency regimes in the power spectrum are analysed. Recognising the very general applicability of our theory, we also mention possible applications to other problems.

    • Infrared intensity analysis of CH2Cl2 and CD2Cl2 in vapour and liquid states

      Pratibha Naik N Rajeswara Rao

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      In the infrared spectra of molecules with more than one C-H bond the symmetric and antisymmetric stretching bonds often overlap, causing uncertainty in the intensity analysis. For CH2Cl2 and CD2Cl2 in the vapour state, the two bands overlap to such an extent that Straley who takes it as one band attributes it to antisymmetric stretching while Saekiet al assign it to the symmetric stretching. Following the method of analysis initiated in this laboratory, we have solved this problem by ultimately obtaining intensities separately forA1 andB2 species. The band is mostly due to the symmetric stretching, 0.06 out of the total of 0.31 contributing toB2. Thus, this gives a method of separating the intensities of bands which are highly overlapping.

    • Impurity effects on the critical behaviour of the electrical resistance of binary liquid mixtures

      Anil Kumar E S R Gopal

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      The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region, both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H2O/D2O impurities.Tc was approached to aboutt=3×10−6 wheret=(TTc)/Tc. The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dTt−b does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the non-critical region. Binary liquid systems seem to violate the universality of the critical resistivity.

    • Pressure induced phase transition in mercurous chloride

      T Ranga Prasad K Satyanarayana Murthy Leela Iyengar K V Krishna Rao

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      Pressure induced phase transition in mercurous chloride has been studied by high pressure x-ray diamond anvil cell. The change in diffraction pattern started and ended at a pressure of about 5 kbar and 20 kbar respectively. The patterns recorded at 20 kbar could be indexed basing on an orthorhombic lattice, with lattice parametersa=4.23 Å,b=4.54 Å andc=10.44 Å.

    • Stochastic theory for clustering of quenched-in vacancies—1. General mathematical properties

      G Ananthakrishna

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      The problem of clustering of quenched-in vacancies into various types of extended defects is considered. A master equation for the evolution of the concentration of clusters of various sizes is written down with general transition rates. It is shown that this model represents a continuous time non-stationary Markoff process. A particular choice of transition rates corresponding to the formation of vacancy loops and stacking fault tetrahedra is considered in some detail. It is shown that this choice of transition rates allows us to obtain the solution for the concentration of the single vacancy units, and hence yields some information on the nucleation time. Further, the transition matrix becomes stationary and doubly stochastic due to the short time constant of the concentration of single vacancy units. This in turn leads to an unphysical stationary state. Finally we show how the rate equations for the irradiated situation can be written down and derive the phenomenological rate equations that are conventionally used.

    • A stochastic theory for clustering of quenched-in vacancies—2. A solvable model

      G Ananthakrishna

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      The model introduced for clustering of quenched-in vacancies in the first part of this series of papers is considered. Using a generating function, the rate equations are converted into a first order partial differential equation for the generating function coupled to a differential equation for the rate of change of the concentration of single vacancy units. A decoupling scheme is effected which gives an exponentially decaying solution with a very short time constant for the concentration of single vacancy units. The differential equation for the generating function is solved for times larger than the time required for the concentration of single vacancy units to reach its asymptotic value. The distribution for the size of the clusters is obtained by inverting the solution thus obtained. Several results that follow are shown to be in reasonably good agreement with the experimental results.

    • Errata

      S Ananda Rao S V Pappu

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