Physics of mag tapes

["Leonard N. Foner" <Foner@YUKON.SCRC.SYMBOLICS.COM>]

    Date: Sat, 16 Sep 89 09:00 EDT
    From: pan@Athena.Pangaro.Dialnet.Symbolics.Com (Paul Pangaro)

      I have been taking cart tapes for SMBX in and out of airport
      security for years now, and sometimes with the same tape a dozen
      times. Coming back from Boston recently I was met with shock from
      the security-person that I was doing this, because "everybody
      else passes them through by hand" and not through the x-ray
      machine.
  
      Anyone really know what those things do, and whether it can, over
      repeated exposures, affect the oxide/fields on the tape?  I
      realize "it is probably better to be safe than sorry" but I was
      curious about the known realities here.
  
      Best,
      PANgaro

The problem is not X-rays.  The problem is that most X-ray generators
have large magnets in them, and their (usually unshielded) magnetic
fields will degauss your tapes.  (The most common way to generate
X-rays is to slam electrons into a metallic target.  While the X-rays,
being photons, aren't deflected by a magnetic field, the initial beam
of electrons is deflected, and the large magnets are used to focus
and direct that initial beam of electrons.)

What you should really be doing is to be careful never to pass the tapes
near the X-ray generator.  This means that handing them around it is
probably more dangerous than taking them through it, if you're careless
and just casually hand them around the machine's case instead of walking
a few feet around it the entire assembly instead.

						<LNF>