A Helium 5 at rest decays into Helium 4 and a neutron.
Mass of Helium 4 = 6.648 x 10^-27
Mass of Neutron = 1.67493 x 10^-27
Helium 4 has a momentum of 1.903 x10^-20 and Ek 2.723x10^-14
v= square root of (E2/m)
The Attempt at a Solution
I have found the mass defect for both Helium 4 and the neutron. and Helium 5.
I think i can use E=mc^2, and then use E in v= square root of (E2/m). I am stuck in trying to figure out what I should use for m? The mass defect on the before or after the decay? Any help appreciated.