What type of radioactive source is typically used in nuclear gauges to measure density?

Cesium-137 is typically used in nuclear gauges to measure density due to its favorable properties for measuring applications. It emits gamma radiation, which can penetrate various materials and provides adequate interaction with the density of the material being measured. Cesium-137 has a half-life of approximately 30.17 years, making it a stable choice for long-term use in measuring instruments.

In the context of nuclear gauges, the gamma radiation emitted by cesium-137 can be detected after passing through the material, allowing for accurate density measurements based on the attenuation of the radiation. This characteristic makes it highly effective in applications such as soil density measurements, asphalt density, and other construction materials.

Other radioactive sources mentioned may not offer the same balance of energy output and half-life that is ideal for density measurements in nuclear gauges, which is why cesium-137 is preferred in this context.