Question

There is a stream of neutrons with a kinetic energy of 0.0327 eV. If the half life of neutron is 700 s, what fraction of neutrons will decay before they travel a distance of 10 m? (mass of neutron = 1.675×10^–27 Kg)

Answer 1

Let m and v denote the mass and speed of neutron. Let N be the initial number of neutrons in the beam. 

Then 1/2 mv² = 0.0327 eV = 0.0327×1.6×10^–19 J

The time dt taken by neutrons to travel a distance of 10 m is 

Since dt is very small as compared to half life of neutrons