• R Shanker

Articles written in Pramana – Journal of Physics

• 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.

• 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

• Contribution of backscattered electrons to the total electron yield produced in collisions of 8–28 keV electrons with tungsten

It is shown experimentally that under energetic electron bombardment the backscattered electrons from solid targets contribute significantly ($\sim 80$%) to the observed total electron yield, even for targets of high backscattering coefficients. It is further found that for tungsten ($Z = 74$) with a backscattering coefficient of about 0.50, about $20$% of the total electron yield is contributed by the total secondary electrons for impact energies in the range of 8–28 keV. The yield of true backscattered electrons at normal incidence ($\eta_{0}$), total secondary electrons (𝛿) and the total electron yield ($\delta_{\text{tot}}) produced in collisions of 8–28 keV electrons with W have been measured and compared with predictions of available theories. The present results indicate that the constant-loss of primary electrons in the target plays a significant role in producing the secondary electrons and that it yields a better fit to the experiment compared to the power-law. • Energy and angular distributions of backscattered electrons from collisions of 5 keV electrons with thick Al, Ti, Ag, W and Pt targets The energy and angular distributions of backscattered electrons produced under the impact of 5 keV electrons with thick Al, Ti, Ag, W and Pt targets are measured. The energy range of backscattered electrons is considered between$E_{B} = 50$eV and 5000 eV. The angle of incidence α and take-off angle 𝜃 are chosen to have values$\alpha = 0^{\circ}$and 10° and$\theta = 100^{\circ}$,$110^{\circ}$and$120^{\circ}$respectively. The measured energy spectra are compared with the available theoretical models for$\alpha = 0^{\circ}$and$10^{\circ}$. The elastic peak intensity of backscattered electrons is found to be a function of angle of incidence, take-off angle and atomic number of the target material. The considered theories are reasonably in good agreement with experiment for the energy spectra of the backscattered electrons having their reduced energies$\epsilon (= E_{B}/E_{0})$in the range of 0.20 to 1.00. • Measurement of the bremsstrahlung spectra generated from thick targets with$Z=2–78$under the impact of 10 keV electrons We present new experimental data on thick target bremsstrahlung spectra generated from the interaction of energetic electrons with bulk matter. The ‘photon yields’ in terms of double differential cross-sections (DDCS) are measured for pure elements of thick targets: Ti ($Z = 22$), Ag ($Z = 47$), W ($Z = 74$) and Pt ($Z = 78\$) under the impact of 10 keV electrons. Comparison of DDCS obtained from the experimental data is made with those predicted by Monte-Carlo (MC) calculations using PENELOPE code. A close agreement between the experimental data and the MC calculations is found for all the four targets within the experimental error of 16%. Furthermore, the ratios of DDCS of bremsstrahlung photons emitted from Ag, W and Pt with those from Ti as a function of photon energy are examined with a relatively lower uncertainty of about 10% and they are compared with MC calculations. A satisfactory agreement is found between the experiment and the calculations within some normalizing factors. The variations of DDCS as a function of Z and of photon energy are also studied which show that the DDCS vary closely with Z; however, some deviations are observed for ‘tip’ photons emitted from high Z targets.

• # Pramana – Journal of Physics

Volume 94, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019