Decay-in-storage is the most common method, However, you mentioned "diagnostic procedure" ... If the material is from an "RIA" kit it may be exempt and you do not have to worry about disposal. Again, check out your source of this material and your local regulatory position (state vs. NRC). Regards, William Lorenzen Children's Hospital 617-355-7516 lorenzen_w@a1.tch.harvard.edu