Then
we can write the conservation of energy Ei = Ef as
2
0
0
1
(2 )(
)
2
4
4
e Ze
Ze
K
d
d
ε
ε
=
=
π
π
Thus the distance of closest approach d is given by
2
0
2
4
Ze
d
εK
=
π
The maximum kinetic energy found in a-particles of natural origin is
7 7 MeV or 1 2 × 10–12 J Since 1/4pe0 = 9