Gamma spectroscopy is used for the determination of radioactivity in food. A coaxial germanium detector is cooled by means of liquid nitrogen in order to avoid thermically induced background noise. The entire gamma spectrum of the sample is recorded. For food analytics, three isotopes are of primary relevance:
- 131I (iodine-131)
- 134Cs (caesium-134)
- 137Cs (caesium-137)
Their activity is measured in Bq/kg. The limit of detection depends on the duration of analysis and on the isotope, but is well below the statutory maximum levels.