Re: arsclist Irradiation of mail

[Jerome Hartke <jhartke@xxxxxxxxxxxx>]

Mike Richter wrote:
> 
> At 10:23 AM 5/14/2002 -0700, Jerome Hartke wrote:
> >Information posted below seems a bit anecdotal. Past postings are
> >confusing because they have not been very specific. Steve's comment
> >regarding "heavy dosage" is not clarifying. "Significantly powerful"
> >anything, including bulldozers and nuclear explosions, can destroy CDs.
> >
> >Regarding x-rays, they do not damage media but the powerful magnets in
> >x-ray machines can erase magnetic media that is placed in proximity to
> >the magnets.
> >
> >Regarding CD irradiation, information posted by Media Sciences at
> >http://www.mscience.com/faq29.html is specific in terms of electron beam
> >energy, dose, using values represented to be in current use by the USPS.
> >Media Sciences does not wish to guarantee any results, but our results
> >do show that media degradation by irradiation of the mail is minimal.
> >
> >If readers are unclear about USPS procedures, they contact their USPS
> >consumer affairs office or USPS packaging specialist.
> 
> One footnote to Jerry's admirable summary, if I may:
> 
> There have been reports of damage to erasable media from airport scanning.
> Given the recording mode on "CD-RW" and properties of modern media, that is
> relatively credible, but I've found no confirming reports in what might be
> considered scientific analysis or test.
> 
> Mike

 I have no ready explaination for how airport scanners affect CD-RW
discs. Most elements interact with magnetic fields. Ag, In, Sb, and Te
that are used in the rewritable layer are diamagnetic, which means they
slightly diminish an externally applied magnetic field. Sb (antimony)
has the largest magnetic susceptibility of -0.87 x 10^-6 cgs. Aluminum
is used in the reflective layer and is paramagnetic (enhances an
external field) with a susceptibility of +0.65 x 10^-6 cgs.

These interactions are not significantly lossy, but I do suppose that
very strong a.c. magnetic fields might induce some heating. The
susceptibility of antimony is slightly greater than that of carbon, and
I am not aware of any problems in that area.

One remote possibility is that magnetic fields have some orientation
effects with diamagnetic atoms that might promote segregation in the
amorphous regions. This is rather far fetched however. Perhaps others
might seek comments from physical scientists at their universities.

I have an active effort to correlate CD-RW test equipment with Philips.
Once that is complete some quantitative tests may help to clarify the
various reports of CD-RW longevity problems.

Jerry
Media Sciences, Inc.

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