Annihilation radiation

Positively charged electrons (Positrons) are emitted from the nucleus as it undergoes β+ decay.

The positron travels a short distance (a few millimeters), depositing any excess energy before it combines with a free electron.

Annihilation radiation is not monoenergetic, unlike gamma rays produced by radioactive decay.

The production mechanism of annihilation radiation introduces Doppler broadening.

[2] The annihilation peak produced in a photon spectrum by annihilation radiation therefore has a higher full width at half maximum (FWHM) than decay-generated gamma rays in spectrum.

A Germanium detector spectrum showing the annihilation radiation peak (under the arrow). Note the width of the peak compared to the gamma ray peaks from radioactive decay visible in the spectrum.