Thick-target X-ray bremsstrahlung spectra produced in 6.5 keV and 7.5 keVe--Hf collisions

The absolute doubly differential cross-sections (DDCS) for production of the thick-target X-ray bremsstrahlung spectra in collisions of 6.5 keV and 7.5 keV electrons with thick Hf target are measured. The X-ray photons are counted by a Si(Li) detector placed at 90° to the electron beam direction. The bremsstrahlung spectra are corrected for various ‘solid-state effects’ namely, electron energy-loss, electron back-scattering, and photon-attenuation in the target, in addition to the correction for detector’s efficiency. The DDCS values after correction, are compared with the predictions of a most accurate thin-target bremsstrahlung theory [H K Tseng and R H Pratt,Phys. Rev. A3, 100 (1971); Kisselet al, Atomic Data Nucl. Data Tables 28, 381 (1983)]. Also, a dependence of the absolute DDCS on atomic numberZ of the targets (₄₇Ag,₇₉Au and₇₂Hf) at 7.0 keV and 7.5 keV electron energies has been studied. The agreement between experiment and theory is found to be satisfactory within 27% systematic error of measurements. However, an apparent systematic difference between experiment and theory in the region of low-energy photons has been explained qualitatively by considering the fact that the hexagonal atomic structure of Hf offers possibly a greater magnitude of ‘solid-state effects’ in respect of blocking the low-energy bremsstrahlung photons from coming out of the target surface than does the cubic-face centered structure of Ag and Au target in similar conditions of the experiment.     

Studies onO-Vanillinoxime as an analytical reagent

o-Vanillinoxime has now been used for the gravimetric determination of copper and nickel alone and in presence of many foreign ions. Copper can be estimated in presence of appreciable amounts of cadmium, zinc, cobalt and lead. The interference due to iron (III), antimony (III), bismuth (III) and tin (II) can be removed by suitable masking agents. Determination of copper and nickel in presence of each other has also been carried out.     

Chemistry of mixed ligand complexes of platinum: crystal and molecular structure of trans-[PtCl(CH3)(PEt3)(AsPh3)]

The dimethyl platinum(II) complex containing mixed ligands, cis-[Pt(CH₃)₂(PEt₃)(AsPh₃)] reacted with one equivalent of hydrogen chloride yielding trans-[PtCl(CH₃)(PEt₃)(AsPh₃)]. The X-ray crystal structure of the molecule shows the trans orientation of the PEt₃ and AsPh₃ ligands.     

SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi

An on-line facility to measure coincidences between the recoil ions and the scattered projectiles (SCORPION) has been designed, fabricated and commissioned at Nuclear Science Centre (NSC), New Delhi. The facility consists of a four jaw slit assembly, a time of flight (TOF) spectrometer, a parallel plate electrostatic charge analyser and a one dimensional position sensitive parallel plate avalanche counter (PPAC). Details of the design and working principles of various components and the test results obtained for the Si ^q+-Ar collision system are presented to highlight the performance of the system. A multiple loss of up to four electrons has been observed for 60 MeV Si⁴⁺ ions colliding with argon atoms in a single collision condition. Spectra of recoil ions detected in coincidence with a particular charge state of the scattered projectile show a bell shaped distribution as a function of the recoil charge state (r) for the electron loss events. However, the yield of recoil ions drops asr increases for the direct ionization channel. Also for electron loss, the peak of the recoil ion distribution is seen to shift to a higher recoil charge state as the number of lost electrons from the projectile increases.     

A 44 GHz HEMT amplifier

A 44-GHz amplifier using 0.25-m gate length and double-heterojunction structure HEMT devices is described. Higher gain and power performance have been obtained from the amplifier using this device at millimeter-wave frequencies. A spot gain of 9.4 dB and a 1-dB gain compression point of +7.5 dBm has been achieved at 43.5 GHz.This work was supported by the Air Force Space Division under Contract No. F04701-84-C-0113.     

Copolymerization of 2-hydroxypropyl methacrylate with alkyl acrylate monomers

2-Hydroxypropyl methacrylate has been copolymerized with methyl acrylate, ethyl acrylate, n-butyl acrylate, and methyl methacrylate in bulk at 60°C using benzoyl peroxide as initiator. The compositions of copolymers have been determined by the estimation of the hydroxyl group by acetylation process. The copolymerization parameters have been determined by conventional scheme of copolymerization.     

Design of Peptides with α,β-Dehydro Residues: Synthesis,Crystal Structure and Molecular Conformation of a Peptide N-Boc-Phe-ΔPhe-Ile-OCH<Subscript>3</Subscript>

To develop a complete set of design rules with α,β-dehydro residues, a tripeptide N-Boc-Phe-ΔPhe-Ile-OCH₃ was synthesized. The synthesis was carried out in solution phase using azlactone procedure. The three-dimensional structure of the peptide was determined by X-ray diffraction method and refined to an R-factor of 0.085. The structure contains three peptide molecules in the asymmetric unit. In all the three crystallographically independent molecules ΔPhe residue adopts one of the three conformations that have been reported for a ΔPhe residue. The overall conformations of three peptide molecules in the asymmetric unit are not similar. Two out of three crystallographically independent molecules adopt type II β-turn conformations whereas the third molecule is found having the characteristic S-shaped conformation in which the values of dihedral angles φ, ψ have opposite signs alternately. One of these two types of conformations has been observed when a ΔPhe is introduced at (i+2) position of a tetrapeptide. The β-turn conformation is stabilized by a 4→1 hydrogen bond where the hydrophobic side chains of residues at (i+1) and (i+3) positions stabilized the unfolded conformation with van der Waals interactions. The three independent molecules are locked together by three hydrogen bonds between molecules A and B and two hydrogen bonds between molecules B and C.     

Ultrasound-assisted conversion of toxic beta-asarone into nontoxic bioactive phenylpropanoid: isoacoramone, a metabolite of Piper marginatum and Acorus tararinowii

Ultrasound-assisted synthesis of bioactive isoacoramone (1), a metabolite of Piper marginatum and Acorus tararinowii, has been achieved by oxidation of toxic beta-asarone (2) with potassium permanganate/copper sulphate/alumina into asaronaldehyde (3) followed by treatment with ethylmagnesium iodide to provide 1-(2,4,5-trimethoxy)phenyl-1-propanol (4) which upon further oxidation with potassium permanganate/copper sulphate afforded 1 in 64% yield (overall 32%). Toxicological evaluation of 1 reveals it to be nontoxic up to 60 mg/kg b.w.     

Development of a Cr(III)-specific potentiometric sensor using Aurin tricarboxylic acid modified silica

A new chelating resin, Aurin tricarboxylic acid modified silica, was synthesized. The resin behaves as a selective chelating ion exchanger for Cr(III) at a pH 3.8-5.5. A polyvinyl chloride-based membrane electrode of the modified silica has been fabricated and explored as sensor for Cr(III) ions. The membrane works well over the concentration range 7.0 × 10⁻⁶ to 1 × 10⁻¹ M of Cr(III) with a Nernstian slope of 19.0 mV per decade of concentration. The response time of the sensor is 10 s and it can be used for a period of 5 months. The performance of the sensor is best in the pH range 3.5-6.5 and it also works well in partially non-aqueous medium. The selectivity coefficient values depicts that the membrane exhibits good selectivity over a number of interfering ions. Moreover, the membrane sensor has been applied to analyse the concentration of chromium in certified steel sample and food materials with greater than 97% accuracy.     

Study of multiple relaxations in styrene-acrylonitrile copolymer using thermally stimulated current method

The dielectric behaviour and the electrical polarization in as-cast and polarized films of styrene-acrylonitrile (SAN) copolymer have been investigated using the Thermally Stimulated Current (TSC) technique. Films were polarized with various field strengths in the range 20 to 80 kV cm^?1. The TSC spectrum showed four peaks (at ～ 70, 105, 130 and ～ 180°); their origins are explained in terms of the relaxation of the nitrile side-groups, glass-transition of the copolymer and the space-charge displacement. Thermal peak-cleaning and partial-heating techniques were applied in order to determine the exact positions of the peaks and the activation energies associated with the processes.