Modifications in track registration response of PADC detector by energetic protons

It has been well established that different ionising radiations modify the track registration properties of dielectric solids. In an effort to study the response of Polyallyl diglycol carbonate (PADC Homalite) detector towards fission fragment, PADC detectors were exposed to 10⁴ Gy dose of 62 MeV protons and then one set of samples were exposed to fission fragments from a ²⁵²Cf source. Two of these detectors were containing a thin layer of Buckminsterfullerene (C₆₀). The study of the etched tracks by Leitz Optical Microscope reveals that the track diameters are enhanced by more than 70% in the proton irradiated zone as compared to that in the unirradiated zone. Scanning Electron Microscopy was performed after etching the sample in 6 N NaOH at 55°C for different etching times, to study the details of the surface modifications due to proton irradiation of PADC detectors with and without C₆₀ layer. Our observations revealed that the diameters and density of proton tracks have increased with etching time on the surface facing the fullerene layer as well as the other surface. However, a relatively more open structure of the etched surface containing C₆₀ as compared to the bare one may be an indication of the extra damage caused by the energy released upon the destruction of C₆₀ molecules by energetic protons.     

Luminescence in ZnS: La and ZnS: (Mn,La) phosphors

The photo (PL) and electro (EL) luminescence in ZnS: MnLa and ZnS: La have been studied. The enhancement and quenching of emission bands have been observed on the simultaneous application of sinusoidal field and photons. The wave shape, voltage, frequency and temperature dependence of EL brightness have been reported. A study of the phosphorescence and thermoluminescence of these phosphors is also carried out and it is observed that the trap-depth changes slowly with temperature and activator concentration. An attempt has been made to calculate the trap depth by studying temperature dependence of EL brightness. The results are reported and discussed.     

Spin-transition in nearly cubic site in [FeII(L)3][PF6]2

The spin-transition (¹A₁?⁵T₂) behaviour of a new mononuclear iron(II) compound [Fe^II(L)₃][PF₆]₂[L = 2-[3-(2′-pyridyl)pyrazole-1-ylmethyl]pyridine] has been investigated by ⁵⁷Fe Mössbauer spectroscopy. Analysis of the Mössbauer spectra revealed low value of the quadrupole splitting of the high-spin state which reflects iron(II) to be in nearly cubic lattice site. Mössbauer spectra under light show the light-induced excited spin state trapping effect and the observed quadrupole splitting of the metastable high-spin state is found little sensitive to the high-spin fraction value. DFT calculations are in progress to document the almost cubic nature of the ligand-field acting on the iron atom.     

A novel confocal optical pulse stretcher for laser pulses

We present an analytical and experimental study of a novel confocal optical pulse stretcher (COPS). The simple and passive pulse stretcher consists of two concave mirrors and a scraper beam-splitter and its optical configuration ensures a perfect spatial overlapping of laser pulses at the beam-splitter. The pulse stretcher is compact and suitable for laser pulses of large divergences. The confocal optical pulse stretcher is demonstrated on a pulsed copper vapour laser to convert a 40 ns (1/e² % points) pulse into a 55 ns with reduction of peak power by a factor of 1.375 without loss of pulse energy.     

Phospholipid/protein cones

The presence of protein in tubule-forming solutions of the diacetylenic phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine results in the formation of hollow cones rather than the expected hollow cylinders. Differential phase-contrast video microscopy reveals that cones grow from proteinaceous nodules in a fashion similar to cylindrical tubule growth from spherical vesicles. Spatially resolved electron-beam energy-dispersive X-ray fluorescence spectroscopy shows the protein to be associated with the cone wall. Small-angle X-ray scattering shows that, like the protein-free cylinders, the cones are multilamellar with essentially identical interlamellar spacing.     

Kinetics and mechanism of the oxidation of n-acetyl l-cysteine by 2,6-dichloroindophenol in methanol–water medium

The principal reactants interact in a molar ratio of 2:1 forming dihydroindophenol and the corresponding disulfide. The order of reaction is unity with respect to each reactant, namely, N-acetyl L-cysteine and indophenol. The rate shows an inverse linear relation with hydroxyl ions. It is not influenced by the variation in the initial concentration of indophenol. The rate increases on adding the salts possessing a cholinergic effect and the neutral electrolytes, as well as on increasing the dielectric constant of the medium. The products, namely, N-acetyl L-cystine (disulfide) and the leuco dye, do not influence the rate. A low energy and a highly negative entropy of activation (4.11 kcal/mol and -60.49 e.u., respectively) suggest the formation of an outer sphere complex as the rate-determining step.     

Lyoluminescence of sensitized glucose

Lyoluminescence studies have acquired considerable significance in recent years due to its potential as a cheap, convenient and versatile method for radiation dosimetry. It has advantages over other conventional techniques due to tissue equivalence of organic lyoluminescent materials and small size in which this type of dosimeter can be used. It is particularly attractive for therapeutic dosimetry. The paper reports the performance of glucose crystallised with known concentrations of sensitizer luminol. It also gives the relative performance of various lyoluminescence materials of similar type being studied currently.     

Kelvin Helmholtz Instability in a Magnetoplasma

Two dimensional transverse Kelvin-Helmholtz (K-H) instability has been studied at the interface between the two fluids (plasma medium) of finite thickness in relative motion to each other. The perturbations on the interface are assumed to be electromagnetic and a dispersion relation is obtained. The interface (boundary) has been found to be unstable for a wide range of perturbation wavelengths (wave numbers kx, ky). It is shown that the modification introduced by electromagnetic (quasi-electrostatic) perturbations in comparison to electrostatic one is to reduce the growth rate of perturbations. The growth rate maximizes when kx = ky. The applications of this study have been discussed to explain some of the observed ionospheric (auroral arc formation) and magnetospheric (unstable magnetopause boundary, hydromagnetic pulsations) phenomena.     

Raman and infrared spectra of tere-phthalaldehyde

The laser Raman spectrum of tere-phthalaldehyde powder has been recorded on a Jobin Yvonhg 2S spectrophotometer with a~100 mW Argon-Ion laser. The infrared spectrum of the solid substance has been recorded on a Perkin-Elmer 621 spectrophotometer in the region 300–4000 cm^-1 using KBr and nujol mull techniques. The observed frequencies have been assigned in terms of the fundamentals, overtones and combinations assumingD _2h point-group symmetry.