Since gamma rays penetrate more deeply through the body than alpha or beta particles, all tissues and organs can be damaged by sources outside the body.

In many cases, some type of dense material is needed to reduce the hazard presented by gamma rays. 

As previously noted, barriers of lead, concrete, or water can provide protection from gamma rays. This is why certain radioactive materials are stored under water or in concrete or lead-lined rooms. This is also why dentists place a lead blanket on patients receiving x-rays of their teeth.