Among the reactions involving protons, the (p, Y) and (p, n) reactions are relatively simple because the emitted particle is neutral. The two reactions are competing reactions, however, with the (p, n) reactions (governed by strong interactions) being more frequent. The threshold energy of (p, n) reactions is about 2—4 MeV, and the reactions are endoergic. In the (p, n) reaction, the number of protons increases and the number of neutrons decreases. The product nuclei are rich in protons, so they usually decompose by positive beta decays or electron captures. Carrier-free radio­active isotopes can be produced. For example:

7Be(p, n)7B (6.27)

An example of the (p, Y) nuclear reaction is

6Li(p, Y)7Be (6.28)

The energy of the emitted photon is extremely high—about 17 MeV. Another example is the

12C(p, y)13N (6.29)

reaction. The product nucleus has positive beta decay; it has some medical applications.

The (p, a) has little importance. The Coulomb barrier acts both on the irradiating proton and on the emitting alpha particle. The reaction is always endoergic. The ratio of neutrons increases, so the product nuclei decompose by negative beta decay. Carrier-free isotopes can be produced. For example:

14N(p, a)11C (6.30)