Performance study of LaBr3:Ce detectors coupled to R2083 PM tube for energy and timing characteristics

Journal of Radioanalytical and Nuclear Chemistry - Performance of 1″?×?1″ LaBr3 (5% Ce) scintillator coupled to Hamamatsu R2083 PM Tube has been investigated for the...     

A moving-load controlled-displacement fracture-toughness testing machine

In conventional fracture-toughness testing, the line of application of the loads remains fixed with respect to specimen geometry. In this testing machine, the load moves with the advancing crack front, and displacement is used as the controlled variable to propagate and arrest a crack. The energy-release rate at the onset of crack propagation and, hence, the plane-strain fracture toughnessK _Ic can be measured directly without compliance calibration or stress-intensity evaluation. The specimen is in the form of a flat plat 25 by 50 cm which is simple to machine and provides about 30 values ofK _Ic. The versatility of the machine is demonstrated by making a statistical analysis ofK _Ic for 7075-T6 Al by showing the effect of plate thickness on the fracture toughnessK _c using a tapered specimen, and by evaluatingK _c in 7075 Al as a function of aging temperature in a thermal-gradient-treated specimen.     

Integral equation formulation for buoyancy-driven convection problems

An integral equation formulation for buoyancy-driven convection problems is developed and illustrated. Buoyancy-driven convection in a bounded cylindrical geometry with a free surface is studied for a range of aspect ratios and Nusselt numbers. The critical Rayleigh number, the nature of the cellular motion, and the heat transfer enhancement are computed using linear theory. Green's functions are used to convert the linear problem into linear Fredholm integral equations. Theorems are proved which establish the properties of the eigenvalues and eigenfunctions of the linear integral operator which appears in these equations.     

Free volume related fluorescent behavior in electron beam irradiated chalcone doped PVA

Effect of electron irradiation on the free volume related microstructural and optical properties of chalcone doped Poly(vinyl alcohol) composite films have been studied using FTIR, UV-Visible, XRD and Positron Annihilation techniques. The FTIR spectral study shows that the irradiation induces the crosslinking within the composite. Using UV-Visible absorption spectra the optical energy band gap and activation energies were estimated and the variation of these parameters suggests the existence of defects and molecular ordering within the irradiated composite. XRD diffractograms reveal that the crosslinking enhances the crystallinity of the sample. In this cross-linked polymer composite the fluorescence enhancement has been observed in the fluorescence spectral study. The Positron annihilation result suggests that the irradiation affects the free volume properties and crosslinking hinders the chalcone chromophore molecular rotation. Under this restricted condition the chromophore molecules likely to emit enhanced fluorescence and its mobility is directly related to the free volume around it.     

Chemical characterization of soda-lime glass samples by in situ current normalised PIGE and conventional INAA methods for forensic applications

Nuclear analytical methods namely in situ current normalised Particle Induced Gamma Ray Emission (PIGE) and conventional Instrumental Neutron Activation Analysis (INAA) were utilized for determining major, minor and trace concentrations of eighteen elements in five soda-lime (automobile) glass samples. Concentration of four major elements (Si, Na, Mg and Al) by PIGE and fourteen elements including ten trace elements by INAA were determined. For forensic application, major elements were used for confirming the class of glass samples, whereas concentration results of trace elements like transition and rare earth elements were utilized for finding similarity or differences among the glass samples.

     

Determination of fluorine concentrations in soil samples using proton induced gamma-ray emission

A non-destructive, in situ current normalized particle induced gamma-ray emission methodology has been standardized for quantification of fluorine (F) in soil samples from Punjab state, India. The samples were irradiated using 4 MeV proton beam from the Folded Tandem Ion Accelerator at BARC, Mumbai. The gamma rays of energies 197 and 478 keV arising from ¹⁹F(p, p′γ)¹⁹F and ⁷Li(p, p′γ)⁷Li nuclear reactions were measured using high resolution gamma-ray spectrometry. The concentration of fluorine in soil samples was found to vary between 414 and 5,746 mg kg^?1.     

Direct evidence of Cd vacancies in CdSe nanoparticles: positron annihilation studies

Poly vinyl alcohol (PVA) capped CdSe nanoparticles having size in the range of 7–17 nm have been synthesized through chemical route and characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Positron coincidence Doppler broadening (CDB) measurements have been carried out in these nanoparticles. It is observed that the electron momentum distributions show a variation in the core electron momentum region with the particle size. In order to examine the influence of defects, first principle calculations of electron momentum distributions in bulk CdSe and in the presence of Cd as well as Se vacancy defects have been performed. Comparison of experimental data with the calculated momentum distribution reveals the presence of Cd vacancy defects, the concentration of which decreases with the increase in the particle size. The present study also indicates possible Se enrichment on the surface of the nanoparticles with the decrease in the particle size.     

Effect of guest-host interaction on the dynamics of ethylene glycol in H-ZSM5 zeolite

Dynamics of ethylene glycol (EG) adsorbed in H-ZSM5 zeolite as studied using quasielastic neutron scattering (QENS) technique is reported here. Analysis of QENS data revealed that observed dynamics correspond to isotropic rotational motion of EG. Rotational diffusion coefficient of EG adsorbed in H-ZSM5 zeolite is found to be slower compared to bulk and comparable to that of benzene adsorbed in the same host. Positron Annihilation Spectroscopy (PAS) technique is used to understand the nature of guest-host interaction and the results of both QENS and PAS are found to be consistent with each other.     

Correlation of soft magnetic properties with free volume and medium range ordering in metallic glasses probed by fluctuation microscopy and positron annihilation technique

Amorphous ribbons of different thicknesses of Co_64.5Fe_3.5Si₁₆B₁₄Ni₂ alloy were synthesized using the melt spinning technique by varying wheel speed. The effect of cooling rate on the ribbon thickness and their soft magnetic properties have been studied. The amorphous structure has been characterized in terms of structural free volume and medium range order (MRO) by positron annihilation spectroscopy and fluctuation electron microscopy techniques. Positron lifetime spectra of amorphous samples showed two lifetime components. The first component was found to be correlated with MRO whereas, the second lifetime component was found to be associated with nanovoid type of defects, and the second component was strongly dependent on processing conditions. It could be established that the coercivity of the amorphous samples produced by the rapid solidification technique mainly depends on the defects formed during processing rather than change induced in MRO.