why does a neutron make a better nuclear bullet thatn a proton?

Answer 1

Because the neutron is not a bullet. Unlike the proton, which has to overcome coulombic resistance to enter the nucleus, the neutron "rolls right in." This is a principle of neutron analysis, when analyzing for the presence of elements. You expose the sample to "thermal neutrons," and you record the characteristic beta-minus emission plus the characteristic gamma rays.