Volume 24, Issue 1-2
January 1985, pages 1-421
pp 1- January 1985
pp 1-14 January 1985 Quantum Physics
We review here classical Bogomolnyi bounds, and their generalisation to supersymmetric quantum field theories by Witten and Olive. We also summarise some recent work by several people on whether such bounds are saturated in the quantised theory.
pp 15-26 January 1985 Quantum Physics
Two special topics in the quantum theory of angular momentum are discussed in this article. They are: (i) the relationship between the coupling and recoupling coefficients (for two and three angular momenta, respectively) and sets of generalized hyper-geometric functions of unit argument; and (ii) the ‘non-trivial’ or polynomial zeros of angular momentum coefficients and their classification.
pp 27-29 January 1985 Quantum Physics
The linearization technique of random phase approximation is applied to the anharmonic oscillator to find a modified perturbation series. It is shown that for the anharmonic termλx4, the ground state energyE0 upto the second order of perturbation is given byE0=(35/48) (3/4)1/3λ1/3 asλ→∞.
pp 31-37 January 1985 Quantum Physics
We propose an analytic perturbative approach for the determination of the Feigenbaum-Cvitanović function and the universal parameterα occurring in the Feigenbaum scenario of period doubling for approach to chaotic behaviour. We apply the method to the caseZ=2 whereZ is the order of the unique local maximum of the nonlinear map. Our third order approximation givesα=2.5000 as compared to “exact” numerical valueα=2.5029 ... We also obtain a reasonably accurate value of the Feigenbaum-Cvitanović function.
pp 39-45 January 1985 Quantum Physics
Fluctuation properties of the regular and irregular energy levels for the Hénon-Heiles Hamiltonian are examined. The spacing distributions and the calculated values of the Δ3-statistic show that there is no difference in the short range correlation properties of these spectra. Remarkably, the Δ3 values agree with the results of random matrix theory.
pp 47-51 January 1985 Quantum Physics
A modification of the Wick-Cutkosky equation for the relativistic bound state of two scalar particles interacting through the exchange of a massless scalar field within the ladder approximation has been considered by incorporating the self-energy diagrams in the integral kernel. An exact analytical solution of the equation is obtained at vanishing total energy and it is shown that the self-energy effects generally diminish the eigenvalues in agreement with the findings of Liet al, who, however solved the equation numerically for the case of massive scalar exchange. An additional feature of the modified equation is that it preserves the 0(5) symmetry at zero total energy as was first noted by Cutkosky for the scalar bound state equation without self-energy effects.
pp 53-62 January 1985 Particle Physics
In a recently suggested variational quantum field theoretical approach the angular momentum and isospin properties of the pion field surrounding a quark bag are investigated using the Lagrangian of the Cloudy Bag Model.
pp 63-68 January 1985 Particle Physics
A current confinement model for glue-balls is proposed to maintain complete similarity with relativistic harmonic oscillator model (rhm) with Lorentz scalar and vector potentials for quarks. The spurious motion of the centre of confinement is accounted for in these models in exactly the same manner. We shall review some of the successes of therhm in hardronic masses, magnetic moments of baryons, nucleonic sizes and polarisability and proton-antiproton annihilation, as well as the recent results on glue-balls.
pp 69-76 January 1985 Particle Physics
Isobaric degrees of freedom δδ in nuclei are determined from the quark cluster model of a nucleus. These additional degrees of freedom are brought in by the coloured quark exchange between different nucleon clusters present in nuclei. They are found to be important in the region of momentum transfer near 3.5 fm−1. The mass dependence of these isobaric degrees of freedom in nuclei turns out to beA5/6.
pp 77-94 January 1985 Particle Physics
In this paper we present a review of our investigations on universal long range force between spins mediated by a massless axial vector gauge field which we name as “axial photon”. The invariance of the Lagrangian field theory of particles, possessing spin degrees of freedom, under local Lorentz transformations, necessitates the introduction of such an axial vector gauge field which interacts with spin current of the particles. Classical as well as quantum dynamics of electrons interacting with photon and axial photon are worked out. The new interaction is found to be asymptotically free. It is shown thatqed can be made finite if the coupling strengths of electron to photon and axial photon can be made equal. Experimental consequences of the existence of axial photon are discussed and the strength of the interaction is estimated by comparing predictions of the theory with experiments.
pp 95-108 January 1985 Particle Physics
Recent experimental data on single hadron production by two-photon beams inpetra andpep have provided a unique opportunity for testing specific models of confinement through a study of one of their cleanest predictionsviz the γγ →H amplitudes. Motivated by this new facility, aqcd-oriented Bethe-Salpeter model of harmonic confinement, which has already been found to describe rather well several classes of hadronic data (from mass spectra to electromagnetic and pionic couplings), is now employed for a detailed comparison of its predictions onP → γγ andT → γγ couplings with the data. The agreement is quite good for all cases except one (η → γγ).
pp 109-117 January 1985 Nuclear Physics
Adiabatic time-dependent Hartree-Fock (atdhf) theory, including the authors’ work in this field, has been summarised. In response to the criticism of Yamamuraet al the role of curvature in preventing the choice ofpurerpa mode as the solution near the static Hartree-Fock minimum has been discussed.
pp 119-130 January 1985 Nuclear Physics
The nucleon exchange process between two nuclei in close proximity and its application to an explanation of fragment mass and charge distributions in fission and in heavy ion deep inelastic collisions are reviewed. An analysis of the measured correlations between the energy loss from relative motion and the fragment mass and charge variances in the heavy ion deep inelastic collisions is presented. The recent data on fragment mass and charge variances as a function of the fragment kinetic energy in thermal neutron induced fission of235U, lends added support to the hypothesis that the nucleon transport process plays a similar role both in fission and in heavy ion deep inelastic collisions.
pp 131-136 January 1985 Nuclear Physics
The angular distribution of long-range alpha particles emitted in keV-neutron induced fission of235U has been measured using a technique which employs only a particle telescope to derive the angular information. The neutron energy region investigated is 100 keV-1 MeV. The angular distribution oflras has been found to be peaked perpendicular to the neutron-direction with a substantial amount of anisotropy near 200 keV.
pp 137-153 January 1985 Nuclear Physics
Since its discovery in 1939, nuclear fission has been extensively studied by various experimental as well as theoretical groups in several countries leading to an understanding of major aspects of this important and complex nuclear reaction. In Trombay, studies have been carried out in the last 25 years using both physical and radiochemical methods and significant contributions have been made towards a better understanding of this reaction. This paper presents highlights of radiochemical studies on fission of actinides, particularly mass, kinetic energy and charge distribution and fragment angular momentum. Results of these studies brought out the important role played by deformation energy surface, spherical and deformed nuclear shells and nucleon pairing.
pp 155-164 January 1985 Nuclear Physics
Studies of prompt radiations emitted in fission were started at Trombay in the late 1950’s by Dr R Ramanna and over the years extensive investigations on the emission of prompt neutrons, gamma ray and K x-rays in fission were carried out with neutron beams fromapsara andcirus reactors. In the early 1960’s studies on the emission of light-charged particles in fission, which is a rare mode of fission, were also started. This paper reviews some of the recent studies on the emission of light-charged particles (lcp) in fission which were carried out with a view to investigate the mechanism oflcp emission, the scission configuration and the dynamics of the last stages of the fission process.
pp 165-177 January 1985 Nuclear Physics
This paper describes the reactor physics methods developed for thermal reactor lattices in India. The formulation of the models introduced is based on energy-dependent integral neutron transport theory. More emphasis was put on the development of lattice cell calculational methods which indeed form the basis of physics design of nuclear reactors. The physical formulation and the cross-sections used were subjected to comprehensive validation tests through analyses of experimental information. The comparison of computed and measured parameters have amply brought out the soundness of the physical formalism and the cross-sections used in our calculational procedures.
pp 179-192 January 1985 Nuclear Physics
The prime requirement of reactor safety combined with the need for high availability of nuclear plants have, in recent years, led to considerable research and development efforts at the Bhabha Atomic Research Centre in the field of reactor safety and control engineering. The areas of special interest have been the development of a fast acting emergency shutdown system, on-line fault detection facility for the reactor protection circuits, enhanced instrumentation capability for measurement of critical plant parameters and computerised systems for plant protection, control, performance evaluation, disturbance analysis, and data acquisition and display with particular attention to the problem of manmachine interface. Some of these recent concepts have been incorporated in safety and control systems of theDhruva reactor which is at present undergoing commissioning trials at Trombay. The special features of these systems are highlighted in the paper. The safety strategy adopted for the reactor and the consequent development of special safety systems are described in detail. The choice of the reactor control scheme and the methodology followed in the design of the automatic power control system are indicated. Campbell instrumentation for measurement of neutron flux or in other words reactor power, extensive use of microprocessors in safety related instrumentation and an improved man-machine interface through suitable design of control room have helped in achieving a high degree of reactor safety. The salient features of these systems are also included.
pp 193-210 January 1985 Nuclear Physics
A vast amount of research and development work has been done in recent years to resolve the issues of relevance to the safety of the Liquid Metal cooled Fast Breeder Reactor (lmfbr). Based on the results of this research as well as on the experience gained from the operation of test and prototypelmfbr’s, a certain consensus is emerging on the safety requirements of a modern sodium-cooled large fast power reactor. The paper reviews the fundamental physics and engineering aspects oflmfbr safety with reference to the Fast Breeder Test Reactor (fbtr) now being commissioned at Kalpakkam, and the proposed larger Prototype Fast Breeder Reactor (pfbr). The elements contributing to the inherent safety of fast reactors are recapitulated followed by description of the philosophy of the plant protection system and the use of engineered safeguards to enhance the safety. Finally, the principles used for the containment of radioactivity are discussed.
pp 211-226 January 1985 Nuclear Physics
This article reviews the engineering development and safety aspects that are relevant to the nuclear power programme being pursued in the country. Some of the important aspects have been discussed in detail bringing out the current status and also the directions for further work.
pp 227-244 January 1985 Nuclear Physics
Accelerator development in India is reviewed with special emphasis on indigenous effort. It started with the 4 MeV cyclotron at the Saha Institute of Nuclear Physics, grew substantially with the installation of the Van de Graaff accelerators at Trombay and really came of age with the 224 cm Variable Energy Cyclotron at Calcutta, which resulted in considerable fall-out of technology. Simultaneously electron linac development has also taken place. Thus the stage is set for developing new types of accelerators such as the electron storage ring synchroton, and a proton/heavy ion synchrotron.
pp 245-258 January 1985 Nuclear Physics
The phenomenology of the Pokaranpne experiment (yield - 12 kiloton oftnt) conducted in a shale-sandstone rock, 107 meters underground, is described with the aid of computations using a one-dimensional spherical symmetric rock mechanics computer code developed by the authors. The calculated values of cavity radius, spall velocity and extent of rock fracturing are in good agreement with the observed values. The principal mechanism for crater formation at Pokaran was spall and the relatively smaller crater dimensions and non-venting of radioactivity gases were due to lower kinetic energy transferred to the shale-sandstone rock.
pp 259-278 January 1985 Atomic And Molecular Physics
Discovery of the neutron in 1932 by Chadwick ushered in a new era of scientific research and technology. The neutron is endowed with unique properties in its mass, life time, spin and magnetic moment etc and every important property has been used in the study of condensed matter, biological molecules, nuclear forces, stellar objects and other fields. Neutron has a wide range of applications in power production, breeding of fissile fuel, radiography, medicine and others.
pp 279-292 January 1985 Atomic And Molecular Physics
The advent of nuclear reactors ushered in an era of increasing number of sources of ionizing radiations. However, the potential of ionizing radiations to cause harmful effects was recognized soon after the discovery of x-rays and radioactivityi.e. long before the building of nuclear reactors. Therefore, protection against ionizing radiations has been of paramount concern and has guided the development of atomic energy and related fields. The advances in technology in general resulted in an increase in accidents causing injury and death. It was realised that even medicines, food additives and a host of other substances of daily use had injurious side effects. Smoking was found to be extremely harmful. From these emerged the concepts of quantitative and relative risks. This article discusses briefly the concept of riskvis-a-vis ionizing radiations and approaches to protection against them.
pp 293-310 January 1985 Atomic And Molecular Physics
An indigenous electron energy loss spectrometer has been designed and fabricated for the study of free molecules. The spectrometer enables the recording of low-resolution electronic spectra of molecules in the vapour phase with ready access to the vacuum ultraviolet region. Electron energy loss spectra of aliphatic alcohols and carbonyl compounds as well as of benzene derivatives have been recorded with the indigenous spectrometer and the electronic transitions in these molecules discussed.
pp 311-316 January 1985 Solid State Physics And Materials Science
The magnetic structures of Fe4N and Mn4N have been redetermined using neutron diffraction. The magnetic form factors, obtained from polarised neutron data have been shown to be different for the face-centred and corner atoms. A qualitative explanation of the structures of Fe4N and Mn4N has been provided from the shapes of the magnetic form factors.
pp 317-350 January 1985 Solid State Physics And Materials Science
The current status of the controversy relating to melting in two dimensions is surveyed. To begin with, a review is given of the seminal work of Kosterlitz and Thouless. This is followed by a discussion of the modifications introduced by Nelson and Halperin. The search for the continuous transitions and the intermediate hexatic phase predicted by these theories is then described, covering both the laboratory as well as simulation experiments. Alternate viewpoints to thekt theory aired recently in the literature are also briefly examined. The paper concludes with an outlook for the future.
pp 351-359 January 1985 Solid State Physics And Materials Science
The positron annihilation method is a new addition to the range of sensitive complementary nuclear techniques available for materials’ research. The preferential sensitivity of positrons towards micro-defect domains which are not assessable by other techniques makes it an attractive tool for many materials science problems. The present paper is intended as a brief introduction on the principle of measurements and its potential is exemplified with the help of results on some metallic and ceramic systems.
pp 361-381 January 1985 Solid State Physics And Materials Science
Development of alloys for reliable performance in extreme radiation environments is vital for the viability of advanced nuclear reactor systems. Over the past decade, there has been a considerable growth in our understanding of the basic processes of radiation damage, the nature of the induced defects, their interaction and migration, and the influence of these on the mechanical behaviour of metals. This understanding has however come mainly from studies in pure metals and dilute alloys, and there are difficulties when applying these concepts to concentrated alloys, particularly of technological interest. The present article, which attempts to bridge this gap, discusses recent research developments and some of the emerging new concepts as applicable to alloy systems. Interstitialcy transport; percolation effects in defect migration; short range and long range ordering and restructuring of alloys; defects and damage behaviour of metallic glasses; synergetic processes and phase instabilities; and finally, swelling, irradiation creep and ductility behaviour of alloy systems are the topics discussed.
pp 383-395 January 1985 Solid State Physics And Materials Science
Surface films on metals and alloys often protect them from reaction with the environment, and hence a knowledge of their protective properties and composition could be invaluable for predicting their corrosion behaviour. XPS (x-ray photoelectron spectroscopy) could provide a quantitative analysis of the chemical composition, the nature of valence states and elemental distribution within the surface films.
The present paper reviews the potential of this technique in corrosion studies. A brief review of the work done on the passivation of iron and iron-chromium alloys and on the inhibition studies on copper base alloys has been given. A few examples of investigations carried out at authors’ laboratory are also included. An attempt has been made to establish a correlation between the compositions of the films formed and corrosion behaviour of carbon steel in 10.5 pH lithium hydroxide solution and of Cu-Ni alloys and sacrificial Al-Zn-Sn alloys in synthetic sea-water.
pp 397-421 January 1985 Solid State Physics And Materials Science
This paper gives a brief review of the important phenomena observed in metallic uranium and ceramic nuclear fuels during irradiation in reactors. The mechanism of irradiation growth, irradiation creep and swelling which are responsible for the dimensional instability of uranium has been described. Important phenomena observed in ceramic nuclear fuels,e.g. fuel densification, fuel restructuring, plutonium segregation, oxygen and fission product migration, irradiation creep, fission gas release and swelling have been discussed. A brief note is included on computer modelling for prediction of fuel element irradiation behaviour.
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