Lead replacement for X-ray shields
In medical and in industrial X-ray systems (e.g. CT systems, analytical apparatuses, security and package scanners) almost exclusively lead (Pb) is used for X-ray shielding. Lead sheets and formed lead components are used as radiation absorption material. The reasons for using lead are the excellent shielding properties, the easy availability, the universal usability, and finally the low purchase costs of lead. The onerous recycling process makes lead expensive despite the low initial procurement costs. In the same time, lead is toxic and poses a health risk to anyone who comes in contact with it.
Therefore, the usage of lead is forbidden in a wide range of consumer and industrial products by the Restriction of Hazardous Substances (RoHS) directive of the European Community (EC). Due to technical limitations of alternative materials, X-ray systems are excluded from RoHS till 2021.
The technical limitations of potential replacement materials are the machinability, the ductility, the mechanical stability, and the resistance against aging due to the X-ray radiation (ionizing radiation) .
One potential candidate for lead replacement are Polymers (containing tungsten (W) particles / powder). The main limiting factor using Polymers for X-ray shieldings is their strong aging behavior under ionization radiation. And again, costs are an issue.
The Refectory Metals molybdenum (Mo) and tantalum (Ta) are further candidates to replace lead. But they are struggling with issues like low machinability (compared to lead), lower shielding performance (especially Mo) and their high costs.
Another candidate would be bismuth (Bi), but due to the brittleness difficult to be processed.
A real alternative to replace lead is the Plansee tungsten heavy alloy Densimet®, processed by Metal Extrusion Moulding (MEM). The foils and sheets have a particularly isotrope and homogeneous microstructure free from any characteristic orientation. The Densimet® is absolutely free from any Polymers and it is a purely metallic material. Furthermore, the MEM process is a cost-efficient manufacturing process. Outstanding mechanical characteristics (formed structural components are possible, made by bending, rolling, or deep drawing) and absolutely no aging due to ionizing radiation makes the Plansee Densimet® most suitable for X-ray shields. Plansee Densimet® complies with the RoHS criteria.