I used a number of x-rays of athlete's injuries in the National Museum of Australia exhibition Sportex in Canberra.
To be on the safe side I copied the x-rays and used them with a push button timed light source in the light box (this has the added benefit of making them an 'interactive'.)
The x-ray department at the local hospital copied the x-rays for a small charge. The visitors love it. 

Dr Marion Stell
National Museum of Australia
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>>> Rick Peifer <[log in to unmask]> 18/03/98 3:02:27 am >>>
In our upcoming Health & Healing exhibit we plan to display a pair of
X-ray films on a standard x-ray light box. Anyone know whether or not
the film will stand up to continuous illumination? Will it fade away?
Will it dry out, crinkle, and crack?

                        Rick Peifer
                        Exhibit Design/Technician
                            NC Museum of History.
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                        919-715-0200x229