The positron decay of 15o goes directly to the ground state

The positron decay of 15_o goes directly to the ground state of 15_N; no excited states of l5N are populated and no y rays follow the beta decay. Yet a source of^15_O is found to emit gama rays of about 0.5 MeV Explain the origin of these gama rays.

Solution

Since the gamma rays are emitted in positron decay of O-15 when the O-15 is in the excited state.

Hence the origin of tue gamma rays is the excited state of O-15.