Effects of X-rays on materials

At the Museum of Cultural History, University of Oslo, we use x-rays
to document both organic and inorganic finds.  Over the years I have
often wondered about the effects of x-rays (which are in fact a form
of very high energy) on materials and whether this method of
documentation is really as non-destructive as it is often claimed to
be.

I understand that for some inorganic objects, such as ceramics,
x-ray radiation is strong enough to change the electron 'pattern'
preserved in the crystalline materials within the clay after firing.
Therefore x-ray documentation of  ceramics taken up in block lifts
may damage future dating analyses, using for example the method of
thermoluminescence dating.

I have asked archaeologists whether they use this method to date
ceramics, however to my knowledge thermoluminescence dating has
never been used here. To be sure--and if possible--we remove a
sample of the ceramic before x-raying the object, but as mentioned,
this is not always possible.  One can also argue that the value of
the documentation one obtains from these x-ray images is very useful
to both archaeologist and conservator, therefore we have continued
to take x-rays of ceramics, however potentially destructive this may
be (unfortunately).

However, with the increasing interest in extraction of ancient DNA,
the question has come up again:  are x-rays capable of damaging the
material--in this case the DNA?  We have in the past used this form
of documentation for egyptian mummies, for archaeological wood, and
composite objects (inorganic+organic). Furthermore, I believe that
easier access to CT-scanning equipment (x-radiation) will increase
its rate of usage in museums for documentation.

Has anyone on this list looked into the matter of x-ray damage on
materials making up museum objects, or in general?  If so, can they
provide some references?  I would like to hear how other
institutions deal with these issues, as the importance of preserving
submicroscopic evidence seems to be increasing with the advent of
new analytical techniques.

Susan Braovac


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                  Conservation DistList Instance 22:33
                Distributed: Saturday, December 6, 2008
                       Message Id: cdl-22-33-018
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