Browsing by Author "M.J. Singh"

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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 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.
Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV Si8+-Ar collisions
(Springer New York, 1998) M.J. Singh; S.K. Goel; R. Shanker; D.O. Kataria; N. Madhavan; P. Sugathan; J.J. Das; D.K. Avasthi; A.K. Sinha
Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV Si8+ ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of "optimized parameters" of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for Ar+ to 4.02 eV for Ar10+. These values are compared with the results reported by earlier workers and are shown to follow a g2-behaviour up to a charge state q = 8+ of the recoil ions. © EDP Sciences Springer-Verlag 1998.
Relative shape of the bremsstrahlung-photon energy spectrum from 7.0-keV electrons on Ag and Au
(1995) S.K. Goel; M.J. Singh; R. Shanker
We have measured the relative shape of the bremsstrahlung-photon energy spectrum from 7.0-keV electrons incident on Ag and Au targets; the targets are thick enough to stop the incident electrons, yet thin enough to transmit a substantial fraction of the radiated photons. Our results for the ratio of double differential cross sections for the bremsstrahlung-photon emission from Ag and Au at 90°to the incident electron beam direction are found to yield excellent agreement with Pratt's theoretical prediction [Comments At. Mol. Phys. 10, 121 (1981);. ul2 Electron Bremsstrahlung ×80: Theory and Recent Developments, Proceedings of the International Conference on X-ray Processes and Inner Shell Ionization, Stirling, Scotland, 1980, edited by D. J. Fabian, H. Kleinpoppen, and L. M. Watson (Plenum, New York, 1981)] on the relative shape of the spectrum; however, the thick-target effect introduces a discrepancy between experiment and theory of about 20%. Also, the calculated absolute efficiency of the detector employed using the theoretical bremsstrahlung cross sections is found to agree with the normalization to the radioactive source within the uncertainty of about 20% in the target thickness. © 1995 The American Physical Society.
SCORPION: A system for coincidences between recoil and projectile ions at NSC, New Delhi
(Indian Academy of Sciences, 1997) M.J. Singh; S.K. Goel; R. Shanker; D.O. Kataria; N. Madhavan; P. Sugathan; J.J. Das; D.K. Avasthi; A.K. Sinha
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 as r 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.
Two-electron processes in the ionization of [Formula Presented] and [Formula Presented] by fast protons
(1996) Bhas Bapat; E. Krishnakumar; C.P. Safvan; M.J. Singh; S.K. Goel; R. Shanker
Measurements on dissociative ionization of [Formula Presented] and [Formula Presented] by fast (16–25 MeV) protons are carried out in an effort to understand two-electron processes in collisional ionization. The high velocity limit of the ratio of cross sections, R, of two-electron processes to one-electron processes obtained from these measurements along with earlier data is used to obtain a universal scaling law for R as a function of projectile charge and energy, irrespective of the sign of the projectile charge. © 1996 The American Physical Society.