R Shanker

Electrical transport properties of CuWO4

The temperature dependence of the electrical conductivity, thermoelectric power and dielectric constant of the antiferromagnetic CuWO4 have been studied in the temperature range 300–1000 K. The conductivity results can be summarised by the equations σI=6.31 × 10−3 exp (−0.29 eV/kT) ohm−1 cm−1 in the temperature range 300–600 K and σII=3.16 × 105 exp (−1.48 eV/kT) ohm−1 cm−1 between 600 K and 1000 K. The thermoelectric power can be expressed byθ=[− 1.25 (103/T) + 3.9] mV/K. Initially dielectric constant increases slowly but for high temperatures its increase is fast.

Polarised raman and infrared spectra and vibrational analysis forα-naphthylamine

The Raman spectrum of polycrystalline α-naphthylamine was recorded in the region 100–4000 cm−1. Polarisation measurements were made in CS2 and CHCl3 solutions. The infrared spectrum was recorded in nujol mull in the region 200–4000 cm−1. The resolution was better than 2 cm−1 and the accuracy of the measurements was within ± 2 cm−1 for all the spectra. Vibrational assignments have been proposed for the observed frequencies. Out of the 54 normal modes of vibrations, 51 modes could be observed experimentally.

Doppler effect in fluorine K-Auger line produced in electron-induced core ionization of SF6.

An experimental evidence is reported on the observation of the Doppler effect in fluorine K-Auger line emitted from a core-ionized SF6 molecule under an impact of 16 keV electrons. The emitting source of the Auger line is found to acquire a kinetic energy of 4.7+/-0.3 keV. We propose that such large energy is released from the Coulomb repulsion taking place between F+ and SF5+ fragment ions under influence of an intense focusing field of the incident electrons. In the presence of the Coulomb field of these ions, the Auger line obtains a polarization P = 76%+/-7%.

Ejected electron-ion coincidence measurements of multiple ionization of argon by 10-24 keV electron impact

The charge state spectra of argon ions produced in single collisions by electrons having energies from 10 to 24 keV with argon atoms have been measured by using the ejected electron-ion coincidence technique. Charge analysis of the ions is accomplished by a time-of-flight mass spectrometer equipped with a channeltron while the ejected electrons are detected by another channeltron, both being used in the pulse-counting mode. The ions and the electrons are detected at 90° to the incident electron beam direction. The relative abundance of argon ions in charge state n up to n = 4 + was deduced from the experiment. The charge state fractions Fn of ions with charge states n are found to be constant in the investigated impact energy range. However, their values are seen to decrease rapidly with n. A good agreement is obtained between our experimental results and the calculations based on inner shell ionization cross sections folded with charge state abundances, which result from the decay of the corresponding initial inner shell vacancies. This agreement supports the idea that the multiple ionization of argon atoms by energetic electrons is caused mainly due to inner shell vacancy production followed by relaxation processes resulting in an increase of the charge state of the generated ion. Further, our results show that the Ar+ ions are produced mainly through dipole transitions while ions having n>1 + are dominantly produced by the non-dipole transitions in the entire energy range of investigation. The partial ionization cross sections for Arn + ions (n = 1-4) are found to be in close agreement with the results of other workers in the overlapping region of impact energies.

Development of an experimental facility for studying atomic-field, bremsstrahlung from keV electrons interacting with atoms and molecules

A dedicated working setup for studying the process of atomic-field bremsstrahlung and its dependence on various parameters for keV electrons incident on a solid or a gaseous target has been indigenously developed. The setup consists of a high vacuum scattering chamber attached with a rotatable X-ray photon detector, a home-built high voltage electron gun with a replaceable tungsten-filament cathode, an isolated floating high voltage system, high vacuum pumping units, various signal processing electronic modules and an IBM PC/XT based 4K-multichannel analyzer. A brief description of the facility is presented. The performance of the facility has been tested by recording the bremsstrahlung spectra from 7.0 keV electrons on thin Ag, Au and 7.5 keV electrons on Hf targets; the corresponding spectra are presented and discussed. The gun can operate in the range of 0–8.0 kV accelerating voltage in the present configuration. Other feasible experiments that can be performed on the setup are also briefly mentioned.

Energy and angular distributions of electrons ejected from CH4 and C3H8 under 16.0 keV electron impact

Relative cross sections, differential in energy and angle, for electrons ejected from CH4 and C3H8 molecules under 16.0 keV electron impact have been measured. Electrons were analyzed by a 45° parallel plate electrostatic analyzer at emission angles varying from 60° to 135° with energies from 50 eV to 1000 eV. The angular distributions of electrons exhibit structures which are found to arise from Coulomb and non-Coulomb interactions. Furthermore, the double differential cross sections of electrons ejected from C3H8 molecule are found to be higher in magnitude than those from CH4. This result supports the fact that the number of ejected electrons participating in collisions with C3H8 molecules is more than that in CH4. Also, the angular distributions of C-K-shell Auger electrons emitted from the target molecules have been studied and shown to be isotropic within the experimental uncertainty

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 Tables28, 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.

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 Siq+-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.

The angular dependence of the backscattering coefficient for 3.0 and 5.0 keV electrons from tungsten

Results for the angular dependence of the backscattering coefficient for 3.0 and 5.0 keV electrons incident on a tungsten target are presented. The values of measured at extreme angles of incidence , namely, at and , are found to be 0.389 and 0.468 for 3.0 keV and 0.429 and 0.524 for 5.0 keV respectively. Experimental data are compared with the available theoretical and experimental results. The agreement between experiment and theory is found to be satisfactory for the low angles of incidence but deviations are observed for higher values. Possible reasons for these discrepancies are pointed out and discussed.