Environmental Engineering Reference
In-Depth Information
Ta b l e 2 . 6
The ratio between the diffusion cross section of elastic ion-atom scattering
σ
and
the cross section of resonant charge exchange
σ
res
and
x
defined by (2.47) at a collision energy
of 0.1 eV in the laboratory frame of reference.
Element
σ
/
σ
res
x
, % Element
σ
/
σ
res
x
,%
H
0.79
3.2
Sr
1.1
5.9
He
0.78
3.1
Mo
0.97
4.8
Li
1.1
6.3
Pd
0.86
3.8
Be
1.1
5.9
Ag
0.93
4.4
N
0.81
3.3
Cd
1.1
6.4
O
0.64
2.1
Sn
0.74
2.8
Ne
0.90
4.2
Xe
0.99
5.0
Na
0.93
4.4
Cs
0.84
3.2
Mg
1.1
5.8
Ba
1.1
5.8
Al
0.83
3.5
Ta
1.1
5.8
Ar
1.1
6.0
W
1.2
7.6
K
0.96
4.8
Re
0.91
4.3
Ca
1.2
7.2
Os
0.95
4.6
Cu
0.75
2.9
Ir
0.95
4.6
Zn
1.1
5.8
Pt
0.88
4.0
Kr
1.0
5.4
Au
0.88
4.0
Rb
0.90
4.2
Hg
0.94
4.6
collision velocities. The influence of elastic ion-atom scattering on the resonant
charge exchange cross section is twofold. On the one hand, curvature of the par-
ticle trajectory draws together the colliding ion and atom and increases the cross
section of resonant charge exchange. On the other hand, at a low collision energy
theresonantchargeexchangeprocessisdeterminedbycaptureinion-atomcolli-
sions, and the cross section of resonant charge exchange is half the capture cross
section, that is, it is
r
α
1
2
σ
e
2
σ
res
(
g
)
D
cap
(
g
)
D
π
,
2
ε
where we assume the polarization character of ion-atom interaction. At larger col-
lision velocities we have the following connection [1] between the collision impact
parameter
and the distance of closest ion-atom approach
r
min
for the polarization
interaction potential between them
r
2
min
1
.
e
2
2
r
4
min
ε
C
α
2
D
For the cross section of resonant charge exchange this gives
e
2
R
0
ε
D
2
R
0
C
4
α
σ
,
(2.46)
res
