1 / 26

Henrik Cederquist, Physics Department, Stockholm University

C 70 and C 60 colliding with slow highly charged ions – a comparison. Henrik Cederquist, Physics Department, Stockholm University. Atomic Physics SU : H. Zettergren, H. T. Schmidt, J. Jensen. and H. Cederquist. CEA Ganil : B. Huber, and B. Manil.

edmund
Download Presentation

Henrik Cederquist, Physics Department, Stockholm University

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. C70 and C60 colliding with slow highly charged ions – a comparison Henrik Cederquist, Physics Department, Stockholm University Atomic Physics SU: H. Zettergren, H. T. Schmidt, J. Jensen and H. Cederquist CEA Ganil: B. Huber, and B. Manil Aarhus University: S. Tomita, S.B. Nielsen, J. Rangama, and P. Hvelplund C60 C70 4th Annual LEIF Meeting Belfast, June 29, 2003

  2. Part of the team (in Stockholm in December 2002): J. Jensen S. Tomita P. Hvelplund S.B. Nielsen J. Rangama H. Cederquist Missing in the picture: H. Zettergren, H.T. Schmidt, and B. Huber

  3. Projectiles: Targets: Xe8+ , Xe16+ , Xe23+ (v= 0.07, 0.10, 0.12 v0) C60, C70 (T=600 °C) Important collision features: A(q-s)+ Hollow ions and atoms E0+E Aq+  E0 C70r+

  4. Similarities and differences in ion-induced fragmentation of C60 and C70 C60 C70 Charge stability limits Kinetic Energy Releases (KER) Fission barriers Competition asymmetric fission/evaporation

  5. Fragmentation modes of excited C60 and C70: Neutral evaporation of small fragments: C60 C60r+C60-2mr+ + C2m (m=1,2,3,4…) C70r+ C70-2mr+ + C2m (m=1,2,3,4…) Asymmetric fission: C70 C60r+C60-2m(r-1)+ + C2m +(m=1,2,3,4…) C70r+ C70-2m(r-1)+ + C2m +(m=1,2,3,4…) Multifragmentation: C60r+many small fragments in low charge states C70r+ many small fragments in low charge states

  6. The experimental technique: Collimated C70 Jet Cylindrical analyzer Xe23+ Vex 0 V -100 V TRIG V1 time-of-flight V2 V3 PSD1 START STOP PSD2 Multi-hit TDC 22+ 21+ C705+ C685+ time-of-flight

  7. (a) Intensity (arb. units) (b) m/q (units of C) Xe8+ - C70 (24 keV) Xe8+ - C60 (24 keV) The C70 powder has high purity (99.4 %)

  8. Similarities in the production of intact C60 and C70 ions:

  9. Xe23+ + C70 Xe (23-s)+ + C70r+ +... Xe23+ + C60 Xe (23-s)+ + C60r+ +... Intensity (arb. units) m/q (units of C)

  10. Relative cross sections for producing intact C70r+ and C60r+ ions in Xe23+-C60 and Xe23+- C70 collisions. C60r+ C70r+

  11. Maximum fullerene charges and Similarities in the fragmentation of C60 and C70 ions

  12. Xe23+ + C70 Xe 20+ + C70r+ +... Light fragments: GATED! Xe23+ + C60 Xe 20+ + C60r+ +... Intensity (arb. units) C709+ GATED! + 2+ C C 15 8 + 7+ C + C 6+ C 9+ C C + 3 C 70 5 70 70 6 8+ C + C Intensity (arb. units) 70 + C 11 2+ C 4 11 4 6 8 10 12 m/q (units of C)

  13. Heavy fragments: 4+ 3+ 5+ C C C 70 70 70 5+ C Xe23+ + C70 Xe 21+ + C70r+ +... 68 4+ 66 C 5+ C 70 68 Xe8+ + C70 Xe 6+ + C70r+ +... 70 3+ C 60 5+ 6+ C C 68 70 10 20 4+ 3+ 5+ C 6+ C C C 60 60 7+ 60 60 C 60 Xe23+ + C60 Xe 21+ + C60r+ +... 56 58 4+ 5+ 3+ C C C 60 60 60 Xe8+ + C60 Xe 6+ + C60r+ +... 6+ C 60 10 20

  14. C68(r-1)+ C58(r-1)+ C2+ C2+ Similarities in kinetic energy releases:

  15. Kinetik energy releases – calibration and resolution Collimator Ion beam Ion beam Warm Xe target (high v(Xe)) ’Cold’ C60-jet (low v(C60)) Xe+ Detector Detector C60+ ~ 40 meV ~ 3 meV Energy resolution Energy calibration

  16. Kinetic Energy Releases (KER’s) for C60r+ asymmetric fission – comparison with other measurements 16 C60r+  C58(r-1)+ + C2+ 17+ Present expt. data for Xe 12 KER’s are insensitive to production method! MIKE Scheier et al., 8 Kinetic Energy Release (eV) MIKE Senn et al., 4 Chen et al., TOF TOF Tomita et al., 0 1 2 3 4 5 6 7 8 9 Charge of final fragment C 58

  17. Kinetic Energy Releases for C70r+ asymmetric fission – comparison with other measurements (Xe16+ and Xe23+ projectiles) C70 KER’s are similar for Xe23+ and Xe16+!

  18. C68(r-1)+ C58(r-1)+ C2+ C2+ Model: Comparisons Kinetic Energy Releases C60/C70 C70 data: 25 23+ Present data Xe 16+ Present data Xe 20 15 Kinetic Energy Release (eV) U C60 data: 10 23+ Xe , C 60 5 et al. Cederquist , C 60 R 0 2 3 4 5 6 7 8 9 10 11 12 Initial charge of C /C , r 70 60

  19. Differences in fragmentation pathways:

  20. Xe23+ + C70 Xe 21+ + C70r+ +... C684+ C685+ C704+ C705+ Xe8+ + C70 Xe 6+ + C70r+ +... C685+ C705+ C704+ C684+ Surprising no such difference for the C60 target!

  21. Xe23+ + C70 Xe 21+ +... Xe8+ + C70 Xe 6+ +... 5+ 5+ C C 68 68 5+ 5+ C C 70 70 200 250 300 200 250 300 Same comparison - projected distributions:

  22. Data for Xe8+ impact! Note!!

  23. 4th Annual LEIF Meeting Belfast, June 29, 2003 Conclusions: The relative cross sections for production of intact C60r+ and C70r+ ions are almost identical as functions of r for a given projectile. The fragmentation spectra are very similar for C70 and C60 indicating similar roles played by asymmetric fission and evaporation – exception: Enhanced production of C60 from C70 Measured Kinetic Energy Releases (KER) for asymmetric fission C70r+  C68(r-1)+ + C2+ are significantly lower than those reported earlier in the literature. KER’s are close for C60 and C70 ionized by Xe23+ - in agreement with the fission process being controlled by a barrier Fission barriers and stability limits are similar for C60 and C70 C70 in intermediate charge states fission after collisions with Xe16+ or Xe23+ but evaporate after collisions with Xe8+ - new phenomena not observed with C60!

  24. Look at the raw data again C60 and C70 really behaves differently with Xe8+ projectiles: Xe8+ + C70 / C60 Xe6+ + C70r+ / C60r+ +... C685+ C705+ C704+ C684+ C604+ C605+ C585+ C584+ Note!

  25. There are some differences even with Xe23+ projectiles: Xe23+ + C70 / C60 Xe21+ + C70r+ / C60r+ +... C684+ C685+ C704+ C705+ C584+ C585+ C604+ C605+

  26. Fission barriers are lower for C70r+ than for C60r+ thus Activation energies for neutral C2-emission must be lower for C70r+ than for C60r+ k=r Ea(C60r+) = Ea(C60) + (Ik(C58)-Ik(C60) ) k=1 k=r Ea(C70r+) = Ea(C70) + (Ik(C68)-Ik(C70) ) k=1 C70 C60

More Related