For head on collision, distance between centres of two deuterons
= r = 2 × radius ⇒ r = 4 fm = 4 × 10–15 m
charge of each deuteron, e = 1.6 × 10–19 C
Potential energy
=

e2

4πε0r

=

9×109(1.6×10−19)2

4×10−15

joule =

9×1.6×1.6×10−14

4×1.6×10−16

keV
P.E. = 360 keV or P.E. = 2 × K.E. of each deuteron = 360 keV
∴ K.E. of each deuteron =

360

2

= 180 keV.
This is a measure of height of Coulomb barrier.