Encapsulated Cesium 137 (Cs-137) check source
Encapsulated Cs-137 check source


Cesium-137 (137Cs) is a radioisotope that has been used in both interstitial and intracavitary brachytherapy. Although Cs-137 decays via beta – decay, it is the daughter nuclide’s subsequent gamma emissions that are responsible for most dose when used as an enclosed source in cancer treatment. Elemental Cesium has a low melting point (28.5°C, 83.3°F) and so is most commonly supplied in the form of insoluble powders or ceramic microspheres doubly encapsulated in stainless steel tubes or needles.

Quick Facts

  • Half life: 30.07 years
    • Activity loss per year: ~2%
    • Clinical Source Life: ~7 years
  • Decay Mode: β
  • γ Energy: 0.662MeV
  • Exposure Rate Constant: Γδ = 3.26\(\frac{R \ cm^2}{mCi \ hr}\)
  • Lead HVL: 5.5mm
Cesium-137 (Cs-137) Decay Scheme
Cs-137 Decay Scheme