A neutron and proton collide with kinetic energy of 150 MeV.

Question

given that a pion has a mass energy of 140 MeV which of the following reactions are allowed. For those that are not allowed is the energy or charge conservation violated or both?

1. n p → n p ∏-

2. n p → p p ∏- ∏0

3. n p → n n ∏

4. n p → p p ∏- ∏-

Answer 1

You are looking at mass and charge.  Input charge is +1.  Input mass is two AMU plus the 150 MeV energy (enough to make one pion with 10 MeV left over for kinetic energy).    

1.  charge of products is neutral, violates charge

2 two pions produced, violates energy

3. charge is neutral, violates charge.

4. charge is neutral, violates charge. Also two pions, violates energy.

None of them is allowed.