← Nuclear Physics

Gamma Decay

Sunday, April 3, 2022

The Gamma Decay Process

Just like an atom, the nucleus in an excited state (such as after decaying via alpha or beta decay) will emit photons, called nuclear gamma rays. These gamma rays can also be absorbed by a nucleus in a ground state to excite it.

Nuclear excited states typically only have half-lives on the order of 10910^{-9} or 101210^{-12} seconds, but there are some instances where decay takes hours, days, or even years.

Once the gamma ray is emitted, the nucleus experiences some recoil to conserve momentum. Since the photon has energy EγE_\gamma and momentum pγ=Eγ/cp_\gamma=E_\gamma/c, the nucleus must recoil with momentum pR=pγp_\text{R}=p_\gamma in magnitude. The associated kinetic energy is


Using a gamma ray to excite a ground state nucleus results in the following relationship:

Eγ=EiEfKREiEfE_\gamma=E_i-E_f-K_\text{R}\approxeq E_i-E_f