• Volume 3, Issue 2

      August 1974,   pages  61-132

    • 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.

    • Study of cosmic ray diurnal variation on a day-to-day basis

      A G Ananth S P Agrawal U R Rao

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      From a careful examination of the diurnal variation of cosmic ray intensity at high energies and the interplanetary field characteristics, the average characteristics of diurnal variation were recently explained by us in terms of a balance between outward convection and field aligned diffusion, the latter arising out of a positive radial density gradient. In this paper, we extend this new concept to explain the large variability observed in the diurnal variation on a day-to-day basis and further demonstrate that the measurement of diurnal anisotropy characteristic of cosmic ray particles on a day-to-day basis can be used directly to infer the nature and scale sizes of interplanetary field parameters. Comparing with the magnetic field vector, we show that this simple concept holds good on more than 80% of days. On the rest 20% of days which have a predominant morning maxima, the diurnal anisotropy characteristics seem to indicate the presence of a significant component of transverse diffusion current in addition to the normal convection and diffusion flow. Such days are found to be present in the form of trains of consecutive days and are found to be associated with abrupt changes in the interplanetary field direction having scale sizes >4 hr. The value ofK/K which is normally about ⩽0.05 is found to be ≈1.0 on non-field aligned days.

    • 22Ne(a, n)25Mg reaction in CONe mantle of massive stars at high temperatures

      B N Kakati H L Duorah

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      The effectiveness of22Ne (a, n)25Mg reaction as a neutron source is examined at high temperatures 0.8⩽T9⩽3.0 (T9 is the temperature in units of 109K). An assembly consisting of12C,16O, and22Ne is considered at the end of helium burning in some massive stars. Alpha particles necessary for this neutron producing reaction are assumed to be due to reactions involving12C and16O nuclei. Assuming22Ne as the only neutron absorber, the number density of neutrons is calculated. The mantles outside the cores of massive stars are possibly the physical sites for these reactions.

    • Study of molecular motions in liquids by electron spin-lattice relaxation measurements, I: Semiquinone ions in hydrogen bonding solvents

      S K Rengan M P Khakhar B S Prabhananda B Venkataraman

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      The electron spin-lattice relaxation times (T1) of a variety of semiquinone ions in hydrogen bonding solvents have been measured by the pulsed saturation recovery technique as a function of temperature (T) and viscosity (η) of the solvent. Also linewidths (ΔH) have been measured in suitable cases in such solvents at low radical concentrations (∼10−4M). It is observed that (i) the temperature and viscosity dependence ofT1 can be fitted to an equation of the form 1/T1=A(T/η)+Bexp(-ΔE/RT) whereA andB are constants and ΔE is an activation energy of the order of 1 kcal mole−1 for these systems; (ii)T1 is essentially independent of the radical concentration within the range 10−3 to 5×10−2M; (iii) the concentration independent part of the linewidth (ΔH) increases linearly with (η/T) at sufficiently low temperatures, and (iv) the (η/T) dependent part ofT1 is sensitive to the size of the semiquinone as well as that of the solvent molecule, whereas the linewidth which is proportional to (η/T) at high viscosity, low temperature region is not sensitive to the size of the semiquinone and that of the solvent. Based on these observations, it is postulated that in hydrogen bonding solvents, three types of motion contribute significantly to electron spin relaxation:

      1. A restricted small step diffusional motion, not involving large changes in the orientation of the molecule, leading to the dominant viscosity dependent contributions toT1 and ΔH, due to spin rotation interaction;

      2. a large amplitude reorientation of the semiquinone, coupled to translational diffusion, resulting in viscosity dependent contributions toT1 and ΔH, throughg-modulation;

      3. a hindred rotation of the semiquinone within the solvent cage, contributing toT1 due to spin rotation interaction.

      The fact thatT1 is not sensitive to the concentration of the radicals, is ascribed to the formation of the solvent cage that prevents the close approach of radicals, thereby rendering radical-radical interactions to be weak mechanisms for relaxation, even at relatively high radical concentrations.

    • Crystal field effects on the saturation magnetic moment of Sm3+ ion in ferronagnetic samarium compounds

      S K Malik R Vijayaraghavan

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      The effects of cubic crystal fields on the saturation magnetic moment of Sm3+ ion in ferromagnetic compounds have been investigated. In samarium compounds with magnetic elements, the exchange fieldHex acting on Sm3+ ion is taken to be proportional to the sublattice magnetization of the magnetic element, while in compounds with nonmagnetic elementsHex is taken to be proportional to the spin average of the Sm3+ ion and is determined self-consistently. In both types of compoundsHex is assumed to be along [001] direction. The saturation magnetic moment is calculated by taking into account the admixture of excited (J=7/2 andJ=9/2) levels into the ground (J=5/2) level of Sm3+ ion by crystal fields and exchange fields. It is shown that depending upon the strength, the crystal fields quench or enhance the magnetic moment from the free ion value, and in some cases force Sm3+ ion to behave effectively like an (L+S) ion rather than an (LS)ion. The crystal fields may have important bearing on the performance of samarium compounds as permanent magnet materials.

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