Henrik Cederquist, Physics Department, Stockholm University
description
Transcript of Henrik Cederquist, Physics Department, Stockholm University
Henrik Cederquist, Physics Department, Stockholm University
4th Annual LEIF Meeting Belfast, June 29, 2003
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,
C70 and C60 colliding with slow highly charged ions – a comparison
and P. Hvelplund
C70C60
Part of the team (in Stockholm in December 2002):
P. Hvelplund
J. Jensen
S.B. Nielsen
S. Tomita
J. Rangama
Missing in the picture: H. Zettergren, H.T. Schmidt, and B. Huber
H. Cederquist
C70r+
Important collision features:
Hollow ions and atoms A(q-s)+
E0+E
E0
Aq+
Projectiles:
Xe8+ , Xe16+ , Xe23+ (v= 0.07, 0.10, 0.12 v0)
Targets:
C60, C70 (T=600 °C)
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
Fragmentation modes of excited C60 and C70:
Neutral evaporation of small fragments:
Asymmetric fission:
Multifragmentation:
C60 r+ C60-2mr+ + C2m (m=1,2,3,4…)
C60 r+ C60-2m(r-1)+ + C2m
+ (m=1,2,3,4…)
C60 r+ many small fragments in low charge states
C70 r+ C70-2mr+ + C2m (m=1,2,3,4…)
C70 r+ C70-2m(r-1)+ + C2m
+ (m=1,2,3,4…)
C70 r+ many small fragments in low charge states
C60
C70
The experimental technique:
Vex
Multi-hit TDC
START
TRIG
STOP
0 V
-100 V
Collimated C70 Jet
tim
e-of
-fli
ght
Cylindrical analyzer
PSD2
V1
V2
V3
C685+
time-of-flight
Xe23+
21+22+
PSD1
C705+
The C70 powder has high purity (99.4 %)
10 20 30 40
C3+
60
C5+
60
C6+
70
C5+
70
C4+
70
C4+
60
C7+
70
C6+
60
C3+
70
C3+
60
C2+
60
C2+
70
(b)
(a)
m/q (units of C)
Inte
nsi
ty (
arb
. un
its)
Xe8+ - C70 (24 keV)
Xe8+ - C60 (24 keV)
Similarities in the production of intact C60 and C70 ions:
10 20 30 40 70
C7+
70 C5+
70
C8+
70
C5+
70
C7+
70
C6+
70
s=1
s=2
s=3
C8+
70
C7+
70
C6+
70
C5+
70
C4+
70 C3+
70
C4+
70
C3+
70
C2+
70
C4+
70
C+
70
C3+
70
C2+
70
m/q (units of C)
Inte
nsi
ty (
arb
. un
its)
Xe23+ + C70 Xe (23-s)+ + C70r+ +...
10 20 30 60
C8+
60
C7+
60
C8+
60
C6+
60C
5+
60
C7+
60
C5+
60
C6+
60
s=1
s=2
s=3C7+
60
C6+
60
C5+
60
C4+
60
C3+
60
C4+
60
C3+
60
C2+
60
C4+
60
C+
60
C3+
60
C2+
60
Xe23+ + C60 Xe (23-s)+ + C60r+ +...
Relative cross sections for producing intact C70
r+ and C60
r+ ions in Xe23+-C60 and Xe23+- C70 collisions.
0 1 2 3 4 5 6 7 8 9 10
10-3
10-2
10-1
s=1 s=2 s=3
rel
Charge of Cr+
70
0 1 2 3 4 5 6 7 8 9 10
10-3
10-2
10-1
s=1 s=2 s=3
rel
Charge of Cr+
60
C60r+
C70r+
Similarities in the fragmentation of C60 and C70 ions
Maximum fullerene charges
and
4 6 8 10 12
C9+
70
C8+
70
C7+
70 C6+
70
4 6 8 10 12
C7+70C
+5
C2+11
C+11
C+6
C+3
C+4
C2+15 C+
8
C6+70C
9+70
C8+70
C709+
Inte
nsi
ty (
arb
. un
its)
m/q (units of C)
Inte
nsi
ty (
arb
. un
its)
Xe23+ + C70 Xe 20+ + C70r+ +...
GATED!
4 6 8 10 12
C9+
60
C2+
11
C+
6
C+
5C+
3
C+
4
C9+
60C
8+
60
C8+
60
C6+
60 C5+
60
C7+
60C
5+
60
C7+
60
C6+
60
Xe23+ + C60 Xe 20+ + C60r+ +...
GATED!
Light fragments:
C7+
60
C6+
60
C4+
60 C3+
60
C6+
60
C5+
60
C5+
60C
4+
60 C3+
60
10 20
C4+
70
C6+
70
C5+
70
C5+
68
C5+
68
C5+
70C
4+
70
C3+
60
C3+
70
10 20
Xe23+ + C70 Xe 21+ + C70r+ +...
Xe8+ + C70 Xe 6+ + C70r+ +...
Xe23+ + C60 Xe 21+ + C60r+ +...
Xe8+ + C60 Xe 6+ + C60r+ +...
6866
5856
Heavy fragments:
Similarities in kinetic energy releases:
C68(r-1)+
C2+
C58(r-1)+
C2+
Kinetik energy releases – calibration and resolution
Detector
Ion beam
C60+
Collimator
’Cold’ C60-jet (low v(C60))
Xe+
Detector
Ion beam
Warm Xe target (high v(Xe))
~ 3 meV ~ 40 meV
Energy resolution
Energy calibration
Kinetic Energy Releases (KER’s) for C60r+ asymmetric fission –
comparison with other measurements
1 2 3 4 5 6 7 8 90
4
8
12
16
Present expt. data for Xe17+
Scheier et al., MIKE
Senn et al., MIKE
Chen et al., TOF
Tomita et al., TOF
Kin
etic
Ene
rgy
Rel
ease
(eV
)
Charge of final fragment C58
C60r+ C58
(r-1)+ + C2+
KER’s are insensitive to production method!
1 2 3 4 5 6 7 8 90
4
8
12
16 Matt et. al., MIKE Senn et. al., MIKE
Present expt. data for Xe23+
Present expt. data for Xe16+
Kin
etic
Ene
rgy
Rel
ease
(eV
)
Charge of final fragment C68
Kinetic Energy Releases for C70r+ asymmetric fission – comparison with
other measurements (Xe16+ and Xe23+ projectiles)
C70 KER’s are similar for Xe23+ and Xe16+!
2 3 4 5 6 7 8 9 10 11 120
5
10
15
20
25
Xe23+
, C60
Cederquist et al., C60
Present data Xe23+
Present data Xe16+
Kin
etic
En
ergy
Rel
ease
(eV
)
Initial charge of C70/C60, r
C70 data:
C60 data:
Comparisons Kinetic Energy Releases C60/C70 C58(r-1)+
C2+
C68(r-1)+
C2+
U
R
Model:
Differences in fragmentation pathways:
C684+ C68
5+C705+C70
4+
Xe23+ + C70 Xe 21+ + C70r+ +...
C704+ C68
4+ C705+ C68
5+
Xe8+ + C70 Xe 6+ + C70r+ +...
Surprising no such difference for the C60 target!
200 250 300
C5+68
C5+70
200 250 300
C5+68
C5+70
Xe23+ + C70 Xe 21+ +... Xe8+ + C70 Xe 6+ +...
Same comparison - projected distributions:
1 2 3 4 5 6 7 8 90
4
8
12
16
Expt. data for Xe23+
Expt. data for Xe16+
Expt. data for Xe8+
Matt et al., MIKE
Expt. data for Xe23+
Expt. data for Xe16+
Matt et. al., MIKE Senn et. al., MIKE
Kine
tic
Ener
gy R
elea
se
(eV)
Charge of final fragment C68
Note!!
Data for Xe8+ impact!
Conclusions:The relative cross sections for production of intact C60
r+ 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 C70
r+ 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
4th Annual LEIF Meeting Belfast, June 29, 2003
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!
C704+ C68
4+ C705+ C68
5+
Xe8+ + C70 / C60 Xe6+ + C70r+ / C60
r+ +...
C604+ C58
4+ C605+ C58
5+
Note!
Look at the raw data again C60 and C70 really behaves differently with Xe8+ projectiles:
C684+ C68
5+C705+C70
4+
Xe23+ + C70 / C60 Xe21+ + C70r+ / C60
r+ +...
C584+ C58
5+C605+C60
4+
There are some differences even with Xe23+ projectiles:
Fission barriers are lower for C70r+
than for C60r+
C60 C70
Activation energies for neutral C2-emission must be lower for C70
r+ than for C60r+
thus
Ea (C60
r+) = Ea (C60) + (Ik(C58)-Ik(C60) )
k=1
k=r
Ea (C70
r+) = Ea (C70) + (Ik(C68)-Ik(C70) )
k=1
k=r