Notes
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Outline
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"Another view"
  • Another view
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Tata Institute, Mumbai (Bombay)
  • TIFR On Arabian Sea
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Introduction
  • Detection of  low energy electrons emitted in atomic collisions provide  crucial information on the various ionization-mechanisms.


  • The e-DDCS spectrum identifies different processes such as  soft electrons (SE), electron capture in continuum (ECC) cusp and the binary encounter (BE).
  • In addition, the e-spectra from H2, is very rich since it can provide the evidence of the interference effect.


  • Since the two H-atoms in molecular hydrogen are indistinguishable, their contributions to the ionization add coherently and an interference effect might be expected.
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VOLUME 87, NUMBER 2        PHYS ICAL RE V IEW LETTERS         9 JULY 2001

Evidence for Interference Effects in Electron Emission from H2
Colliding with 60 MeVu Kr34+ Ions
N. Stolterfoht et al.
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                                                                                                                                RAPID COMMUNICATIONS
PHYSICAL REVIEW A 67, 030702(R) (2003)
Interference effects in electron emission from H2 by 68-MeV’u Kr33ø impact:
Dependence on the emission angle
N. Stolterfoht et al.
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Experimental Details
  • The electrons emitted from H2 were detected by an hemispherical electrostatic analyzer between 1  and 1000 eV for 10-12  angles between 150 and 1500.


  • We show “fully measured” (Experiment with atomic Hydrogen ) interference oscillation for relatively lower collision energies:
  • 1-2.5 MeV/u C6+ and F9+ on H2/H.


  • Also derived the oscillations  using Calculated DDCS for H :   6 MeV/u C6+ + H2.
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Experimental Setup
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Block Diagram
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Energy Distribution
6 MeV/u C6+ + H2
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6 MeV/u C6+ + H2.:45o,75o.
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Interference in backward angles.
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“Fully Measured” interference structure.
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Comparison between different methods.
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Absolute DDCS for H and ratio
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Conclusions
  • Interference effect is not only a phenomena of high energy collisions. It is important at relatively low collision energies also.


  • The dependence of the oscillations on the projectile atomic number is very weak.


  • First study of “fully measured” ratios giving a direct evidence of the interference effect.
  • Present method is free from:
  • i)   the normalization procedure.
  • ii)  choice of theoretical parameters like ZT
  • iii) systematic experimental errors.
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References
  • [1] N. Stolterfoht et al., Phys. Rev. Lett., 87 023201 (2001).


  • [2] M.E. Gallasi et al.,  Phys. Rev A 66, 052705 (2002).


  • [3] L. Nagy et al., J. Phys. B 35, L453 (2002).


  • [4] Deepankar Misra et al., ( Accepted in Phys. Rev. Lett.,)
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6 MeV/u C6+ + H2: 300
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6 MeV/u C6+ + H2: 600
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Experimental Technique
  • Electron spectroscopy:


  • ****C60 vapour source (450-500o C)
  • *** Hemispherical Electron Analyzer.
  • *** Preaccleration voltage = +5V
  • *** m-metal shielding used to reduce mag. Field (below 5 mG)
  • *** Gas pressure kept low : 0.1 mTorr
  • *** electrons between 1 eV to 6 keV
  • ****12 angles between 200 – 1600 degree
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"Lokesh C Tribedi"
  •    Lokesh C Tribedi


  • Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India
  • Students:
  •            U.Kadhane
  •            D. Misra
  •             Y.P.Singh, Aditya Kelkar : Post doc: Ajaykumar
  •  Sc. And Tech. Staff : K.V.Thulasiram
  •                W. Fernandez   And Pelletron Accelerator Staff
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X-ray set up with Pelletron
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Typical Lyman x-ray spectra
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The ratio of Lyb/ Lya for solid and gas
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Lya intensity for solid and gas
Effect of wake field and Stark mixing
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Wake phenomena and e-density fluctuations: Echenique, Ritchie, Brandt;  and Burgdoerfer
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Comparison of the ratio i.e. C60 / N2
  •  Difference ~ 15%\i() (for capture)
  •  Model predicts ~ 10%
  •  Other mechanisms: Post collisional effect!
  • Effect of Giant dipole polarization and Stark mixing!
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A comparative study
  •     ions   Z/ V    Quantity   Solid st. effect   td (s)
  • Kr36+   1.0      Ly ratio     20-25%        ~ 10-15
  •  S16+    1.3      Ly-ratio      15%            ~5.10-17
  •  Cl17+   1.4       Ly ratio      20 %         ~5.10-17
  • Si/S/Cl   1.1-1.5     REC   40-50%
  • C/O/F     <0.5-1      REC    No measurable effect
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Ly ratio in collisions with Cl17+
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E-DDCS spectrum of C60
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Future?
  • A new ion source, 14.5 GHz ECR source, (obtained from Pantechnik, France) will be installed dedicated mainly for atomic collisions in the low energy region.
  • It will be coupled with a 300 kV accelerator.
  • High resolution x-ray, electron spec, ToF
  • Noble gas cluster/ fullerenes
  • May be coupled with a laser
  • ………..
  • ………..
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Electron density distribution along trajectory in C60
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We are at work!! Electron spectroscopy set up
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