9. [4 points] An isotope of helium with mass 5 u breaks up from rest into a nucleus of ordinary helium (assume: mass = 3 u) plus a neutron (assume: mass = 2 u). The rest energy liberated in the break-up is 0.8 MeV, which is shared (not equally) by the products.
a) Using energy and momentum conservation, find the kinetic energy of the neutron.
b) The lifetime of the original nucleus is 2.1 x 10^{-20}s. What is the minimum width of the range of neutron kinetic energies we would measure in the laboratory as a result of the uncertainty relationship?