Single-cavity 8 MeV race-track microtron

This paper describes the operational details of the single-cavity race track microtron of this laboratory. The machine is capable of providing electrons of 8 MeV energy at 1 mA peak current. Important parameters of the machine and beam handling system are studied and the results are reported.     

Investigation of anomalons in He fragments

We have studied the mean free path of He fragments from projectile beams of Ar, Fe and Kr of energy 1 ? E ?2A GeV at different distances $\text{(L ? 2.5}\text{cm}\text{)}$ from their production point and found that they are the same, independent of their (i) energy, (ii) target size, (iii) target excitation, (iv) He multiplicities and (v) production angles.     

Properties of participants and spectators in non-peripheral Fe-induced reactions at 1.7 A GeV

Central relativistic Fe-induced heavy ion reactions in emulsion have been isolated and we observe that a clean-cut thermal participant-spectator model fails in predicting the experimental angular distributions of charged particles.     

Improved resonance in microtrons by orbit shaping

Microtron electron accelerators generally show a 50% reduction of the injected beam in the first orbits. A modification of the race-track magnet system is proposed in this paper to reduce the beam losses. Calculations of the phases of electrons at the microwave cavity yield exact shapes of different orbits required for resonance in a split magnet system. Introduction of small sector magnets in the field-free space provides a feasible method for obtaining the calculated orbit shapes.     

Uniqueness,reciprocity theorem,and plane waves in thermoelastic diffusion with a fractional order derivative

In this work, a theory of thermoelasticity with diffusion is taken into consideration by using the methodology of fractional calculus. The governing equations for particle motion in a homogeneous anisotropic fractional order generalized thermoelastic diffusive medium are presented. Uniqueness and reciprocity theorems are proved. The plane wave propagation in the homogeneous transversely isotropic thermoelastic diffusive medium with fractional order derivative is studied. For the two-dimensional problem, there exist a quasi-longitudinal wave, a quasi-transverse wave, a quasi-mass diffusion wave, and a quasi-thermal wave. From the obtained results, the different characteristics of waves, like phase velocity, attenuation coefficient, specific loss, and penetration depth, are computed numerically and presented graphically. Some special cases are also discussed.     

Ferroelastic detwinning of the high-temperature superconductor YBa2Cu3O7-δ

Crystals of YBa₂Cu₃O_7-δ (YBC) were prepared using a flux technique. The as-grown crystals were typically on the order of 200 μm × 200 μm × 50 μm, where the 50 μm dimension is in the c-direction. Ferroelastic behavior was observed by applying a uniaxial stress along the [100]_tet-direction using a specially-designed fixture which was mounted to a programmable hot/cold stage of a polarizing reflected-light microscope. Domain wall motion was observed for temperatures greater than 200°C, and complete poling was accomplished at stresses on the order of 50–100 MPa at temperatures of 350–400°C. An ionic diffusion-activated mechanism is suggested.     

Physical property characterization of bulk MgB<Subscript>2</Subscript> superconductor

We report synthesis, structure/micro-structure, resistivity under magnetic field [ρ(T)H], Raman spectra, thermoelectric power S(T), thermal conductivity κ(T), and magnetization of ambient pressure argon annealed polycrystalline bulk samples of MgB₂, processed under identical conditions. The compound crystallizes in hexagonal structure with space group P6/mmm. Transmission electron microscopy (TEM) reveals electron micrographs showing various types of defect features along with the presence of 3–4 nm thick amorphous layers forming the grain boundaries of otherwise crystalline MgB₂. Raman spectra of the compound at room temperature exhibited characteristic phonon peak at 600 cm^-1. Superconductivity is observed at 37.2 K by magnetic susceptibility χ(T), resistivity ρ(T), thermoelectric power S(T), and thermal conductivity κ(T) measurements. The power law fitting of ρ(T) give rise to Debye temperature (Θ_D) at 1400 K which is found consistent with the theoretical fitting of S(T), exhibiting Θ _D of 1410 K and carrier density of 3.81 × 10²⁸/m³. Thermal conductivity κ(T) shows a jump at 38 K, i.e., at T_c, which was missing in some earlier reports. Critical current density (J_c) of up to 10⁵ A/cm² in 1–2 T (Tesla) fields at temperatures (T) of up to 10 K is seen from magnetization measurements. The irreversibility field, defined as the field related to merging of M(H) loops is found to be 78, 68 and 42 kOe at 4, 10 and 20 K respectively. The superconducting performance parameters viz. irreversibility field (H_irr) and critical current density J_c(H) of the studied MgB₂ are improved profoundly with addition of nano-SiC and nano-diamond. The physical property parameters measured for polycrystalline MgB₂ are compared with earlier reports and a consolidated insight of various physical properties is presented.     

Polyaniline–graphene oxide nanocomposites: Influence of nonconducting graphene oxide on the conductivity and oxidation‐reduction mechanism of polyaniline

The present endeavor focuses on the unusual interactions between polyaniline and graphene oxide (PANi–GO) which radically affects the properties of nanocomposites as it is an emerging material for many potential applications. A series of nanocomposites have been synthesized by varying the weight percentage of highly nonconducting GO with respect to aniline which exhibit superior properties in terms of shelf life, processability and conductivity due to the synergistic effect of GO and PANi. A comparison of the resistances of samples reveal that though as‐synthesized GO is insulating (80 MΩ), when added to PANi (283 kΩ) in small amounts yields conducting composites (50–280 Ω). Up to 5 weight % concentration, GO renders conductivity to the composite probably by increasing the doping level of PANi. Nonetheless, no further increase in conductivity observed on addition of more than 5 wt% GO in the composite has dictated us to unravel the structure property relationship between PANi and GO, where GO facilitates the formation of partially reduced phase of PANi, thereby restricting the electronic transport. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3778–3786