Radioactivity: Gamma decay

Gamma decay

In α and β decay, the daughter nucleus is in the excited state most of the time. The typical life time of excited state is approximately 10^-11s. So this excited state nucleus immediately returns to the ground state or lower energy state by emitting highly energetic photons called γ rays. In fact, when the atom is in the excited state, it returns to the ground state by emitting photons of energy in the order of few eV. But when the excited state nucleus returns to its ground state, it emits a highly energetic photon (γ rays) of energy in the order of MeV. The gamma decay is given by

Here the asterisk(*) means excited state nucleus. In gamma decay, there is no change in the mass number or atomic number of the nucleus.

Boron (¹²₅B ) has two beta decay modes as shown in Figure 8.25:

(1) it undergoes beta decay directly into ground state carbon (¹²₆C ) by emitting an electron of maximum of energy 13.4 MeV.

(2) it undergoes beta decay to an excited state of carbon (¹²₆C^*) by emitting an electron of maximum energy 9.0 MeV followed by gamma decay to ground state by emitting a photon of energy 4.4 MeV.

It is represented by