Which isotope is commonly used as the density source in gauges?

Which isotope is commonly used as the density source in gauges?

• A. Uranium-238
• B. Strontium-90
• C. Cesium-137
• D. Iodine-131

Answer: (C)

Density gauges determine density by measuring how gamma rays are attenuated as they pass through a material. The source needs to emit penetrating gamma radiation with a stable, long enough half-life for field use and a well-understood emission energy. Cesium-137 fits best because it provides 662 keV gamma rays that penetrate soils and similar materials effectively, while its roughly 30-year half-life makes it practical for long-term use in gauges. The other options don’t fit as well: strontium-90 is a beta emitter and won’t provide the needed gamma attenuation measurements; uranium-238 is mainly an alpha emitter with complex radiation characteristics; iodine-131 is a medical isotope with a shorter half-life and not intended for industrial gauging.

Density gauges determine density by measuring how gamma rays are attenuated as they pass through a material. The source needs to emit penetrating gamma radiation with a stable, long enough half-life for field use and a well-understood emission energy. Cesium-137 fits best because it provides 662 keV gamma rays that penetrate soils and similar materials effectively, while its roughly 30-year half-life makes it practical for long-term use in gauges. The other options don’t fit as well: strontium-90 is a beta emitter and won’t provide the needed gamma attenuation measurements; uranium-238 is mainly an alpha emitter with complex radiation characteristics; iodine-131 is a medical isotope with a shorter half-life and not intended for industrial gauging.