Radioactive Isotopes in Process Measurement

Overview:

An Objective Look at the Roles of Cesium-137 and Cobalt-60 in Nuclear Measurement Systems for Industrial Processes

Level and density measurements in process control are performed by a number of technologies. When the process temperature, pressure, or chemistry is an issue, then nuclear measurement systems have the advantage. These are non-invasive to the vessel and unaffected by the process pressures and chemistries.

Overall, a nuclear measurement system used for process control consists of a gamma energy emitter and detector. An emitter is placed on one side of a vessel to broadcast a beam of energy to the opposite side of the vessel. The detector is placed in the beam on the opposite side of the vessel. The detector will scintillate in the presence of gamma energy and register counts proportional to the field strength. When the process value (level or specific gravity) is low, the detector will register a high number of counts since less gamma energy is blocked by the process material. When the process value is high, more of the gamma energy is blocked which leads to fewer counts.

The two most common gamma emitters used for level and density process measurements are isotopes of cobalt and cesium. The goal of this article is an objective comparison of the roles of cesium-137 and cobalt-60 in process measurement. This will be accomplished by reviewing the properties of the two materials and then comparing the use of the materials in process measurement.