# Cesium-137

#### Background

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$$\frac{R \ cm^2}{mCi \ hr}$$