Question

A
 tritium
 nucleus
 explodes
 by
 beta
 decay.
 An
 electron
 leaves
 with






1x108m/sec. 
Its
 mass 
is
9x10‐31kg.
 What 
is 
the 
recoil
velocity 
if 
the
 3He+
 







ion
 mass 
is
 3x
1.66x10‐27kg.

 What 
is 
the 
kinetic 
energy 
of 
both 
particles








in 
Joules 
and 
in 
electron volts 
(1eV
=
1.16x
‐19J)?


Answer 1

If this were really a two-particle "explosion", then the recoil momentum of the 3He++ particle would be equal and opposite to that of the electron. One could use that fact and the mass to calculate the 3He++ velocity.

Actually, beta decay is a three-particle process, with a variable and often large part of the momentum carried away by an antineutrino. Whoever made up the question should be aware of that.

See
http://hyperphysics.phy-astr.gsu.edu/Hbase/Nuclear/beta.html