It’s quite feasible as there are a number of British and American Valves (Vac Tubes) that have varying levels of radioactive isotope – usually Cobalt-60 or Radium-226.

This list may be of use to you…

http://www.tubecollector.org/documents/radioactive.htm

What is most dangerous with Vac Tubes is their fragility and likelihood that they will be or become damaged when the item containing them is being removed/dismantled. It would then be possible to ingest these products as dust, or get them into a cut etc.

HTH.