half-life of cobalt-60 is shorter (5.3 years for cobalt-60 versus 30 years for cesium-137) thus lowering significantly the useful lifetime of the source. Shielding challenges can be addressed in part by switching from lead shields to more effective tungsten or depleted uranium shielding, but tungsten shielding is more expensive than lead and manufacturing depleted uranium shielding is a very specialized, expensive operation. The shorter useful lifetime of radiation sources requires that they be replaced periodically, which entails transportation of a fresh source and, in some cases, the used source, with the attendant risks associated with source transportation.
X-ray generators are already commercially available as substitutes for applications that do not require gamma rays with the definite energies emitted by cesium-137, and cobalt-60. x-ray tubes can be expensive and require more maintenance than radioactive sources for periodic calibration and replacement. There is new innovation in x-ray irradiators by at least two companies and more replacements for radionuclide radiation sources could come with some incentives.