Cesium/Caesium-137 (Cs-137)

Cesium-137 is widely used throughout the construction industry for level, moisture, and thickness gauging applications. Cesium is also commonly used in medical research & treatment and oil well drilling.

Our Cs-137 sealed source designs provide a cost-effective alternative to OEMs, meeting or exceeding regulatory requirements for sealed source encapsulations.

Source Data

Half Life: 30 Years
Primary Emission: Gamma
Primary Energy: 661 KeV
RWL: 15 Years
Capsule Materials: MP35N; stainless steel.

Cesium-137 History

Cesium-137 (or Caesium-137)  was discovered by and an undergraduate at UC Berkely, Margret Melhase in 1941. Historically, the most important use for cesium has been in research and development, primarily in chemical and electrical applications.

Cesium-137 Applications

  • Thickness Gauging - Cesium-137 is used in the measurement of light alloys, glass, plastics, and rubber for which beta sources are not suitable.
  • Oil Well Logging (OWL) - Cesium encapsulations are used to characterize rock strata during oil well logging applications such as wireline logging and logging while drilling.
    • Cesium-137 sources are designed to withstand forces encountered during oil well logging without compromising encapsulation integrity.
  • Flow Gauging - Cesium and a detector are placed on opposite sides of the material to be measured. Gamma radiation transmitted through the sample is then directed related to the sample thickness.  
  • Level Gauging - Cs-137 is used to monitor process fluids without making physical contact with package contents.
  • Medical - Gamma rays from Cesium are used in radiotherapy as a treatment for brachytherapy.


Measured by National Labs and Statistically verified by QSA. Standard Certificates available upon request.

Custom Design Services

QSA has a large standard product list available to fit your application. Custom Cs-137 source designs are possible for large orders. Contact QSA for more information.

Quality Control

QSA  uses a multi-part quality assurance system to ensure Cesium-137 radiation sources meet the highest integrity levels in the industry, including all statutory and international regulatory requirements.

  • Wipe Test I - Cesium-137 sources are wiped with a swab or tissue, moistened with ethanol or water, then measured for removed activity.
  • Immersion Test II - Cesium-137 sources are immersed in a suitable liquid at 50┬░C for at least 4 hours, then measured for removed activity.
  • Bubble Test III - Cesium-137 sources are immersed in water or a suitable liquid, and the pressure in the vessel is reduced to 13kPa (100mm Hg). No bubbles must be observed.


Contact QSA for additional information on our Cesium-137 sealed source designs.