Browsing by Author "R. Shanker"

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A study of the mean kinetic energy of recoil ions from ion-charge-resolved electron spectra produced in 3.5 keV electron-argon collisions
(Elsevier B.V., 2019) Suman Prajapati; Sunil Kumar; Bhupendra Singh; Bhartendu K. Singh; R. Shanker
New experimental results for the dependence of mean kinetic energy (MKE) of argon recoil ions of charge state 1+ to 4+ on energy selected correlated Auger electrons produced in 3.5 keV electron impact with thermal argon atoms using TOF mass spectrometry and electron spectroscopy techniques are presented. Values of the MKE of recoil ions are deduced from the width of the TOF peaks. The measured average values of MKE of Ar+, Ar2+, Ar3+and Ar4+ recoil ions are found to be respectively 216 meV ± 5 meV, 247 meV ± 6 meV, 290 meV ± 7 meV, and 324 meV ± 8 meV in the electron energy range of 125–210 eV. The average charge state ratios (∑nσn/∑σn) of recoil ions have been determined to be 1.8, 2.4 and 2.0 in the electron energy range of 125–145 eV, 150–200 eV, and 200–210 eV respectively. For the investigated electron energy range 120–210 eV, the considered Auger transitions are found to dominate the direct ionization; for low electron energies (<100 eV), the direct multiple ionization dominates which has not been considered in this work. Survey of results obtained from the present measurements suggests that the MKE depends not only on the charge state of the recoil ions but also weakly on the specific energy range of ejected electrons in the considered collision reaction. Presently we are not aware of any theoretical calculations that can be compared with our results. © 2018 Elsevier B.V.
Absolute double differential cross sections of bremsstrahlung produced from 4.0 ke V electrons incident on free ar atoms
(MDPI AG, 2020) Suman Prajapati; Bhupendra Singh; Sunil Kumar; Bhartendu Kumar Singh; C.A. Quarles; R. Shanker
New results are reported on the measurements of absolute double differential cross sections (DDCSs) of bremsstrahlung produced from 4.0 keV electrons incident on free Ar atoms in the angular detection range of 45°-120°. A significant reduction of the thick target bremsstrahlung (TTB) of the chamber wall and of the photon transmission windows has been achieved by modifying the experimental set-up used previously; a large reduction of TTB in the present experiments is supported by the results of our model calculations for the ratio of TTB background to the normal bremsstrahlung (NB) spectrum carried out for the employed geometry of the experimental set-up. The results of photon energy distribution measured at different angles and those of angular distributions of photons of a given energy are compared with theoretical predictions of Kissel-Quarles-Pratt (KQP) theory for ordinary bremsstrahlung and with predictions of total bremsstrahlung including polarization bremsstrahlung (PBS) of the stripping approximation (SA). A satisfactory agreement observed between experiment and predictions using SA theory for absolute DDCSs of bremsstrahlung provides evidence for an appreciable contribution of polarization bremsstrahlung at the considered impact energy of electrons on one hand, while on the other hand, it exhibits a large discrepancy (about a factor of 2) in DDCSs of bremsstrahlung photons obtained by experiment and by KQP theory for photon energy distributions at all detection angles measured in these experiments. In addition, present results of the angular dependence of photons of different energies show anisotropic distributions and they are found to be in reasonable agreement with both KQP and SA theories. The satisfactory agreement between experiment and theory for angular distributions is an indication of a significant reduction of the background produced from TTB photons. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
Absolute doubly differential cross section for bremsstrahlung spectra produced in 7.0 keV e--Ag and Au collisions
(1997) S.K. Goel; R. Shanker
The first experimental data are presented for the absolute doubly differential cross section (DDCS) for non-characteristics (bremsstrahlung) X-ray spectra produced by 7.0 keV electron bombardment of (semi-thick) targets of silver and gold at a photon detection angle of 90°. The bremsstrahlung spectra are corrected for detector's efficiency as well as for target effects; namely, electron energy loss, backscattering and photon-attenuation in the target. The DDCS values so obtained are compared with the predictions of a thin target bremsstrahlung theory. The agreement between experiment and theory for DDCS both in magnitude and shape is found to be satisfactory within the systematic experimental uncertainty of about 27%. The other solid-state effects, for example, the random motion of penetrating electrons into the thick targets and the depth distribution of photons generated inside the targets are expected to be also present in the interaction. However, the contributions of these effects to the DDCS have not been taken into consideration. Various possible reasons for the existing discrepancy between experiment and theory are pointed out. © 1997 IOS Press.
An apparatus to study the energy and angular distributions of electron-bremsstrahlung photons from gaseous targets
(2014) Namita Yadav; Pragya Bhatt; Raj Singh; B.K. Singh; C.A. Quarles; R. Shanker
An apparatus is developed to measure the energy- and angular distributions of bremsstrahlung generated from collisions of energetic electrons with isolated atoms and molecules. A considerable reduction of thick target bremsstrahlung (TTB) background produced by scattered electrons from the chamber wall is achieved. Details of the experimental setup with regard to design of its components, experimental technique, data acquisition and analysis etc. are given and discussed. The reliability and performance of the setup are demonstrated by obtaining some test results on angular- and energy distributions of bremsstrahlung produced in collisions of 4.0. keV electrons with free argon atoms. These results are compared with the theoretical predictions of the ordinary- and the polarization bremsstrahlung emissions. In this comparison, the experimental data for energy distributions of BS photons are found to be in reasonable agreement while they are found to have noticeable differences in shape of angular distributions. © 2013.
An experimental set up for studying the fusion edge plasma facing materials using TOF mass spectrometry
(Elsevier, 2015) Sunil Kumar; Pragya Bhatt; B.K. Singh; Ajai Kumar; R. Shanker
A new experimental set up is developed to study the fusion edge plasma facing materials under impact of low-energy (40-10,000 eV) atomic and molecular ions. The primary ions are obtained from a low-pressure D.C. gas discharge Colutron ion source. The product ions resulting from the ion-surface interactions involving different processes, for example, surface-induced dissociation (SID), surface-induced reaction (SIR), chemical- and sputtering are detected and identified by using a single-field linear time-of-flight (TOF) mass spectrometer coupled with a time- and position-sensitive dual micro-channel plate detector. The mass spectra of secondary ions are recorded by employing a pulsed extraction and acceleration technique. The experimental set up, experimental technique and data acquisition methodology are presented and discussed. A test experiment is conducted on the developed set up to demonstrate the performance and reliability of the apparatus. For this, a primary beam of 427 eV N2+ ions was chosen to interact with a hydrocarbons covered surface of platinum target kept at room temperature. SID of N2+ into N+ and TOF mass spectra of sputtered, reflected and chemically formed ions from the ion-surface interaction are analyzed. A noticeable feature in the spectra is observed which shows that the odd-electron ions of sputtered hydrocarbons are preferentially produced in the interaction in addition to the other product ions. The nominal mass resolution (M/ΔM) of the present tandem mass spectrometer system is estimated to be about 600, while energy and spatial spreads of the primary ion beam are determined to be about 518 meV and 2.8 ± 0.3 mm respectively. The survival probability of the incident ions is found to be 6.6% suggesting that the major process of ion-surface interaction at the considered impact energy is neutralization. © 2015 Elsevier B.V. All rights reserved.
An experimental setup for studying the core-excited atoms and molecules by electron impact using energy analysed electron–ion coincidence technique
(Scientific Publishers, 2017) S. Kumar; S. Prajapati; B. Singh; B.K. Singh; R. Shanker
Operation and performance of an apparatus for studying the decay dynamics relevant to core–hole decay processes in atoms and molecules excited by energetic electrons using an energy analysed electron–ion coincidence technique are described in some detail. The setup consists of a time- and position sensitive double-field linear TOF mass spectrometer coupled with a dual MCP detector and a single-pass CMA to select the energy of detected electrons. Details of different components involved in the setup are presented and discussed. To demonstrate the performance and capability of the apparatus, we present some typical results extracted from the TOF argon ion-mass spectra observed in coincidence with 18-energy selected electrons emitted from interaction of a continuous beam of 3.5 keV electrons with a dilute gaseous target of argon atoms. Specifically, the variation of relative correlation probability for the final ion-charge states Ar1+ to Ar4+ produced in the considered collision reactions as a function of energy of emitted electrons is determined and discussed. © 2017, Indian Association for the Cultivation of Science.
Angular and impact energy dependence of intensity ratio of K α,β x-rays to underneath bremsstrahlung radiation emitted from 15 to 25 keV electrons incident on a pure thick Cu (Z=29) target
(Elsevier Ltd, 2019) Bhupendra Singh; Suman Prajapati; B.K. Singh; R. Shanker
We present new results on angular and impact energy dependence of the relative intensity ratios of K α and K β characteristic (CS) x-ray lines to their respective underneath bremsstrahlung (BS) radiation produced from 15-25 keV electrons incident on a thick polycrystalline pure target of Cu (Z = 29). The angular distributions of relative intensity ratios were carried out by measuring the radiations emitted at incidence angle θ i that varied from 15° to 75° in reflection geometry mode of the target. The x-rays emerging from the target surface were detected by an energy dispersive Si PIN photodiode detector. The magnitude of relative intensity ratio of K α /BS is found to be larger than that of K β /BS by a factor of about 5.11, 5.24 and 5.49 for 15 keV, 20 keV and 25 keV impact energy, respectively measured, for example, at θ i = 15°. However, the intensity ratio of a given characteristic line to its underneath BS increases on average by a factor of about 2.2 in varying the impact energy from 15 keV to 25 keV measured at different angles. The experimental results on angular and impact energy dependence are compared with the corresponding results obtained from Monte-Carlo simulations using the PENELOPE code. The overall agreement between experiment and theory is found to be satisfactory within the uncertainty of measurements. © 2019 Elsevier Ltd
Angular and impact energy dependence of intensity ratio of K x-rays to bremsstrahlung radiation emitted from 10-25 keV electrons incident on a pure thick Cu (Z=29) target
(American Institute of Physics Inc., 2019) Suman Prajapati; Bhupendra Singh; B.K. Singh; X. Llovet; R. Shanker
The variation of relative intensity ratios of the characteristic K x-ray lines, namely, K and K to that of the underneath BS radiation as a function of incidence angle 150-750 under bombardment of 10-25 keV-electrons on a pure thick target of polycrystalline Cu (Z=29) in the reflection geometry mode using a Si PIN photodiode detector has been studied.The comparison of experimental results with those of MC simulations using PENELOPE code shows a good agreement between experiment and theory within the error of measurements for both angular and energy dependence of the considered ratios. The details of these results are presented and discussed in this work. © 2019 American Institute of Physics Inc.. All rights reserved.
Angular dependence of Kβ/Kα intensity ratios of thick Ti and Cu pure elements from 10–25 keV electron bombardment
(Scientific Publishers, 2018) B. Singh; S. Kumar; S. Prajapati; B.K. Singh; X. Llovet; R. Shanker
Measurements yielding the first results on angular dependence of Kβ/Kα X-ray intensity ratios of thick Ti (Z = 22) and Cu (Z = 29) targets induced by 10–25 keV electrons are presented. The measurements were done by rotating the target surface around the electron beam direction in the angular detection range 105° ≤ θ ≤ 165° in the reflection mode using an energy dispersive Si PIN photodiode detector. The measured angular dependence of Kβ/Kα intensity ratios is shown to be almost isotropic for Ti and Cu targets for the range of detection angles, 105° ≤ θ ≤ 150°, while there is a very weak increase beyond 150° for both targets. No dependence of Kβ/Kα intensity ratios on impact energy is observed; while on average, the value of the Kβ/Kα X-ray intensity ratio for Cu is larger by about 8% than that for Ti, which indicates a weak Z-dependence of the target. The experimental results are compared with those obtained from PENELOPE MC calculations and from the Evaluated Atomic Data Library (EADL) ratios. These results on Kβ/Kα X-ray intensity ratios are found to be in reasonable agreement in the detection angle range 105° ≤ θ ≤ 150° to within uncertainties, whereas the simulation and experimental results show a very slight increase in the intensity ratio with θ as the latter attains higher values. The results presented in this work provide a direct check on the accuracy of PENELOPE at oblique incidence angles for which there has been a lack of measurements in the literature until now. © 2018, Indian Association for the Cultivation of Science.
Backscattering of 8-28 keV electrons from a thick Al, Ti, Ag and Pt targets
(2006) R.K. Yadav; R. Shanker
Measurements of electron backscattering coefficient η for thick Al, Ti, Ag and Pt targets have been made for incident electrons with energy 8-28 keV. The variations of η with angle of incidence α, impact energy E 0 and with target atomic number Z have been studied. The data are compared with available theories. The mean fractional energy absorbed in the backscattering process has been determined and compared with an analytical expression and with Monte-Carlo simulations based on the Kanaya and Okayama electron-electron and electron-nucleus interactions and on the Quinn electron-plasma interactions. The comparison between our experimental data and the model calculations using Monte-Carlo simulations and analytical expression shows a reasonably good agreement among themselves within experimental errors of measurements. © 2005 Elsevier B.V. All rights reserved.
Backscattering of 8-28 keV electrons from a thick tungsten target
(2003) R.K. Yadav; Argala Srivastava; S. Mondal; R. Shanker
The backscattering process of 8-28 keV electrons from a thick tungsten target is studied. Measurements on the variation of the backscattering coefficient, η, with angle of incidence α and with diffusion range xd for different impact energies are presented and discussed. Simple analytical expressions based on continuous energy-loss and diffusion of incident electrons inside the target are used to examine the above variations. Over the entire ranges of impact energy and angle of incidence of the present studies, the predictions of the analytical relations are found to be in good agreement with most of our data and with those of earlier workers within experimental errors of measurement.
Bremsstrahlung spectra produced from kilovolt electrons incident on thick targets of Ti, W and Pt
(Institute of Physics Publishing, 2008) A.N. Agnihotri; V.S. Subrahmanyam; R.K. Yadav; R. Shanker; X. Llovet
Measurements of x-ray emission spectra generated by 10-20 keV electrons impinging normally on bulk targets of pure elements Ti (Z = 22), W (Z = 74) and Pt (Z = 78) have been performed using an experimental setup developed for studying electron-atom/molecule collisions in our laboratory. Values extracted from the experimental data for bremsstrahlung yield, integrated yield and mean energy of the bremsstrahlung radiation beam for the above collision systems have been compared with the simulation results obtained from the general purpose Monte Carlo simulation code PENELOPE. The comparisons are found to show a satisfactory agreement between them within their statistical uncertainties. Some apparent mismatches are observed for which possible causes and their origins are discussed. © 2008 IOP Publishing Ltd.
Characteristic and non-characteristic X-ray yields produced from thick Ti element by sub-relativistic electrons
(2012) Namita Yadav; Sunil Kumar; Pragya Bhatt; Raj Singh; B.K. Singh; R. Shanker
Measurements are performed to study the electron impact energy dependence of doubly differential bremsstrahlung yields (DDBY) and of characteristic Ti Kα line yields produced from sub-relativistic electrons (10-25 keV) colliding with a thick Ti (Z = 22) target. The emitted radiation is detected by a Si-PIN photo-diode detector with energy resolution (FWHM) of 180 eV at 5.9 keV. The measured data of DDBY are compared with the results predicted by Monte-Carlo (MC) simulations using the general purpose PENELOPE code. A reasonable agreement is found between experimental and simulation results within the experimental uncertainty of measurements of 12%. Characteristic Ti K α yields are obtained for the considered impact energy range and they are compared with the existing theoretical results. A good agreement is found between the present measurements and the theoretical calculations. Furthermore, data are presented for impact energy dependence of the ratio K α/(Kα+ Kβ) of a thick Ti target under impact of 10-25 keV electrons. The ratio shows a very weak dependence on impact energy in the studied range. The average value of the ratio is found to be 0.881 ± 0.003. © 2012 Elsevier B.V.
Coincidence electron spectroscopy of electron-impact multiple ionization of argon
(American Physical Society, 2005) S. Mondal; R. Shanker
Measurements of the partial double differential ionization cross sections of argon atoms have been made by performing coincidences between recoil ions and energy- and angle-selected slow electrons produced in 12-24 keV e- -Ar collisions. Results show that the Ar3+ ions are formed mainly by a two-step-one process via electron shake-off. These measurements have enabled determination of the shake-off probability S=0.14±0.01 for L2,3 subshell, which is in good agreement with a theoretical predication. Additionally, Ar2+ and Ar+ ions are found to arise respectively from the filling of L -shell vacancy by an auger transition and from the direct ionization of M -shell of the argon atom. © 2005 The American Physical Society.
Coincidence studies of quasimolecular electron emission in 700-keV Ar2+-Kr collisions
(1989) R. Shanker; U. Werner; R. Bilau-Faust; R. Hippler; U. Wille
Continuum electron emission following 700-keV Ar2+-Kr collisions has been investigated by detecting electrons in coincidence with projectile ions scattered through laboratory angles between 5°and 20°. From the analysis of the experimental data in terms of quasimolecular Auger-electron emission, molecular-orbital binding energies at small internuclear distances as well as collision-broadening parameters have been inferred. The results indicate that the electron emission is dominated by the decay of 4s and 4p vacancies in the highly charged Ar-Kr quasimolecule. The analysis also reveals the presence of an exponentially decreasing high-energy tail of the spectra, which cannot be ascribed to quasimolecular Auger electrons and which has not been taken into account in previous analyses. © 1989 The American Physical Society.
Contamination of potable water by enterotoxigenic Escherichia coli: qPCR based culture-free detection and quantification
(2011) C.B. Patel; P. Vajpayee; G. Singh; R.S. Upadhyay; R. Shanker
Tourists visiting to endemic zones may acquire Enterotoxigenic Escherichia coli (ETEC) infection resulting into diarrhea due to consumption of contaminated potable waters. In this study, a qPCR assay (SYBR Green), targeting LT1 and ST1 genes was designed to quantify ETEC in potable waters derived from civic water supply. The assay could detect lowest 1. CFU/PCR targeting LT1/. ST1 gene from ten-fold diluted culture of the reference strain (E. coli MTCC 723) and is ten-fold more sensitive than the conventional PCR. The quantification of the ETEC in potable waters collected from civic supply of a major city of the northern India exhibiting high flow of tourists reveals that all the sites that ran along sewage line were contaminated by the ETEC. Contamination was due to percolation of sewage. The assay could be used for the regular monitoring of potable water in places exhibiting heavy flow of tourists to prevent ETEC induced diarrhea. © 2011 Elsevier Inc.
Contribution of backscattered electrons to the total electron yield produced in collisions of 8-28 keV electrons with tungsten
(2007) R.K. Yadav; R. Shanker
It is shown experimentally that under energetic electron bombardment the backscattered electrons from solid targets contribute significantly (∼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 (η0), total secondary electrons (δ) and the total electron yield (δtot) 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. © Indian Academy of Sciences.
Design and fabrication of a time-of-flight spectrometer for studies of multiple ionization of gases by charged particle impact
(Indian Academy of Sciences, 2002) R.K. Singh; R.K. Mohanta; M.J. Singh; R. Hippler; S.K. Goel; R. Shanker
A time-of-flight spectrometer has been designed and fabricated for measuring the charge state distributions of target ions produced in collisions of keV-electrons with gaseous target atoms/molecules. The design details of the spectrometer and the description of experimental procedures for optimizing various parameters are presented and discussed. The working principle of the spectrometer, its time- and mass-focussing conditions, transmissions and detection efficiency etc. are given. A few typical test runs on multiple ionization of Ne and Ar gas atoms are illustrated. These spectra are found to yield the time resolution of about 10 ns for Ar4+ ion peak in 24.0 keV e- - Ar collisions while the mass resolution of the spectrometer is obtained about 10% at mass m = 20.
Development of a new experimental setup for studying collisions of keV-electrons with thick and thin targets
(Indian Academy of Sciences, 2002) R.K. Singh; R.K. Mohanta; R. Hippler; R. Shanker
Development of a new electron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering, innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0 keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based 8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design, fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray spectrum are illustrated to exhibit the satisfactory performance of the developed setup.
Development of an experimental facility for studying atomic-field, bremsstrahlung from keV electrons interacting with atoms and molecules
(Springer India, 1995) S.K. Goel; M.J. Singh; R. Shanker
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. © 1995 Indian Academy of Sciences.