GamXRAY is a shielding material developed for gamma radiation protection.  Its performance is closer to that of pure lead than any of the popular materials in current use.  It is non-toxic, non-lead, nano-type material.

GamXRAY is discussed, and its properties compared to three materials currently popular for gamma radiation shielding, in the document: GamXRAD


Two excellent general discussions of Dirty Bombs are:

1 - Security of Radioactive Sources
2 - Commercial Radioactive Sources, Surveying the Security Risks