12 MeV neutron... how fast is it going?

Answer 1

Dear Johannes,
The kinetic energy of the neutron
Ke=12Mev
and 1 eV = 1.602 E−19 Joules.
Ke=.5 m v^2
E=(12E+6 )(1.602 E−19)=1.92 E-12 J
E=
then
v=sqrt(2(1.92 E-12) /m)
since m=1.67 E−27

v=sqrt(2 x 1.92 E-12 / 1.67 E−27 )
v=47.95 E6 m/sec

Answer 2

Since the neutron is traveling about 16% of light speed we can compare the relativistic calculation.

mass
--------- =1/sqrt(1-v^2 / c^2)
rest mass

the rest mass of a neutron is 939.565 Mev/c^2. The mass will be 12Mev more than this.

939.565 + 12
-------------------=1.0127718678
939.565

From this v/c = 0.15831
So v = 47.46 E 6 m/sec